This is gnugo.info, produced by makeinfo version 4.11 from gnugo.texi.
INFO-DIR-SECTION GNU games
* GNU Go: (gnugo). The GNU Go program
File: gnugo.info, Node: The Owl Code, Next: Combinations, Up: Pattern Based Reading
The life and death code in `optics.c', described elsewhere (*note
Eyes::), works reasonably well as long as the position is in a
"terminal position", which we define to be one where there are no moves
left which can expand the eye space, or limit it. In situations where
the dragon is surrounded, yet has room to thrash around a bit making
eyes, a simple application of the graph-based analysis will not work.
Instead, a bit of reading is needed to reach a terminal position.
The defender tries to expand his eyespace, the attacker to limit it,
and when neither finds an effective move, the position is evaluated. We
call this type of life and death reading "Optics With
Limit-negotiation" (OWL). The module which implements it is in
There are two reasonably small databases
`patterns/owl_defendpats.db' and `patterns/owl_attackpats.db' of
expanding and limiting moves. The code in `owl.c' generates a small
move tree, allowing the attacker only moves from `owl_attackpats.db',
and the defender only moves from `owl_defendpats.db'. In addition to
the moves suggested by patterns, vital moves from the eye space
analysis are also tested.
A third database, `owl_vital_apats.db' includes patterns which
override the eyespace analysis done by the optics code. Since the
eyeshape graphs ignore the complications of shortage of liberties and
cutting points in the surrounding chains, the static analysis of
eyespace is sometimes wrong. The problem is when the optics code says
that a dragon definitely has 2 eyes, but it isn't true due to shortage
of liberties, so the ordinary owl patterns never get into play. In
such situations `owl_vital_apats.db' is the only available measure to
correct mistakes by the optics. Currently the patterns in
`owl_vital_apats.db' are only matched when the level is 9 or greater.
The owl code is tuned by editing these three pattern databases,
principally the first two.
A node of the move tree is considered `terminal' if no further moves
are found from `owl_attackpats.db' or `owl_defendpats.db', or if the
function `compute_eyes_pessimistic()' reports that the group is
definitely alive. At this point, the status of the group is evaluated.
The functions `owl_attack()' and `owl_defend()', with usage similar to
`attack()' and `find_defense()', make use of the owl pattern databases
to generate the move tree and decide the status of the group.
The function `compute_eyes_pessimistic()' used by the owl code is
very conservative and only feels certain about eyes if the eyespace is
completely closed (i.e. no marginal vertices).
The maximum number of moves tried at each node is limited by the
parameter `MAX_MOVES' defined at the beginning of `engine/owl.c'. The
most most valuable moves are tried first, with the following
* If `stackp > owl_branch_depth' then only one move is tried per
* If `stackp > owl_reading_depth' then the reading terminates, and
the situation is declared a win for the defender (since deep
reading may be a sign of escape).
* If the node count exceeds `owl_node_limit', the reading also
terminates with a win for the defender.
* Any pattern with value 99 is considered a forced move: no other
move is tried, and if two such moves are found, the function
returns false. This is only relevant for the attacker.
* Any pattern in `patterns/owl_attackpats.db' and
`patterns/owl_defendpats.db' with value 100 is considered a win: if
such a pattern is found by `owl_attack' or `owl_defend', the
function returns true. This feature must be used most carefully.
The functions `owl_attack()' and `owl_defend()' may, like `attack()'
and `find_defense()', return an attacking or defending move through
their pointer arguments. If the position is already won, `owl_attack()'
may or may not return an attacking move. If it finds no move of
interest, it will return `PASS', that is, `0'. The same goes for
When `owl_attack()' or `owl_defend()' is called, the dragon under
attack is marked in the array `goal'. The stones of the dragon
originally on the board are marked with goal=1; those added by
`owl_defend()' are marked with goal=2. If all the original strings of
the original dragon are captured, `owl_attack()' considers the dragon
to be defeated, even if some stones added later can make a live group.
Only dragons with small escape route are studied when the functions
are called from `make_dragons()'.
The owl code can be conveniently tested using the `--decide-owl
LOCATION' option. This should be used with `-t' to produce a useful
trace, `-o' to produce an SGF file of variations produced when the life
and death of the dragon at LOCATION is checked, or both.
`--decide-position' performs the same analysis for all dragons with
File: gnugo.info, Node: Combinations, Prev: The Owl Code, Up: Pattern Based Reading
It may happen that no single one of a set of worms can be killed, yet
there is a move that guarantees that at least one can be captured. The
simplest example is a double atari. The purpose of the code in
`combination.c' is to find such moves.
For example, consider the following situation:
Every `X' stone in this position is alive. However the move at `*'
produces a position in which at least one of four strings will get
captured. This is a _combination_.
The driving function is called `atari_atari' because typically a
combination involves a sequence of ataris culminating in a capture,
though sometimes the moves involved are not ataris. For example in the
above example, the first move at `*' is _not_ an atari, though after
`O' defends the four stones above, a sequence of ataris ensues
resulting in the capture of some string.
Like the owl functions `atari_atari' does pattern-based reading. The
database generating the attacking moves is `aa_attackpats.db'. One
danger with this function is that the first atari tried might be
irrelevant to the actual combination. To detect this possibility, once
we've found a combination, we mark that first move as forbidden, then
try again. If no combination of the same size or larger turns up, then
the first move was indeed essential.
* `void combinations(int color)'
Generate move reasons for combination attacks and defenses
against them. This is one of the move generators called from
* `int atari_atari(int color, int *attack_move, char
defense_moves[BOARDMAX], int save_verbose)'
Look for a combination for `color'. For the purpose of the
move generation, returns the size of the smallest of the
* `int atari_atari_confirm_safety(int color, int move, int *defense,
int minsize, const char saved_dragons[BOARDMAX], const char
Tries to determine whether a move is a blunder. Wrapper
around atari_atari_blunder_size. Check whether a combination
attack of size at least `minsize' appears after move at
`move' has been made. The arrays `saved_dragons[]' and
`saved_worms[]' should be one for stones belonging to dragons
or worms respectively, which are supposedly saved by `move'.
* `int atari_atari_blunder_size(int color, int move, int *defense,
const char safe_stones[BOARDMAX])'
This function checks whether any new combination attack
appears after move at (move) has been made, and returns its
size (in points). `safe_stones' marks which of our stones
are supposedly safe after this move.
File: gnugo.info, Node: Influence, Next: Monte Carlo Go, Prev: Pattern Based Reading, Up: Top
* Influential Concepts:: Conceptual Outline of Influence
* Territory and Moyo:: Territory, Moyo and Area
* Influence Usage:: Where influence gets used in the engine
* Influence and Territory:: Influence and Territory
* Territorial Details:: Details of the Territory Valuation
* The Influence Core:: The Core of the Influence Function
* The Influence Algorithm:: The algorithm of `accumlate_influence()'
* Permeability:: Permeability
* Surrounded Dragons:: Surrounded Dragons
* Influential Patterns:: Patterns used by the Influence module
* Influential Display:: Colored display and debugging of influence
* Influence Tuning:: Influence tuning with view.pike
File: gnugo.info, Node: Influential Concepts, Next: Territory and Moyo, Up: Influence
13.1 Conceptual Outline of Influence
====================================
We define call stones "lively" if they cannot be tactically attacked,
or if they have a tactical defense and belong to the player whose turn
it is. Similarly, stones that cannot be strategically attacked (in the
sense of the life-and-death analysis), or that have a strategical
defense and belong to the player to move, are called "alive". If we
want to use the influence function before deciding the strategical
status, all lively stones count as alive.
Every alive stone on the board works as an influence source, with
influence of its color radiating outwards in all directions. The
strength of the influence declines exponentially with the distance from
Influence can only flow unhindered if the board is empty, however.
All lively stones (regardless of color) act as influence barriers, as do
connections between enemy stones that can't be broken through. For
example the one space jump counts as a barrier unless either of the
stones can be captured. Notice that it doesn't matter much if the
connection between the two stones can be broken, since in that case
there would come influence from both directions anyway.
From the influence of both colors we compute a territorial value
between -1.0 and +1.0 for each intersection, which can be seen as the
likely hood of it becoming territory for either color.
In order to avoid finding bogus territory, we add extra influence
sources at places where an invasion can be launched, e.g. at 3-3 under
a handicap stone, in the middle of wide edge extensions and in the
center of large open spaces anywhere. Similarly we add extra influence
sources where intrusions can be made into what otherwise looks as solid
territory, e.g. monkey jumps. These intrusions depend on whose turn we
All these extra influence sources, as well as connections, are
controlled by a pattern database, which consists of the two files
patterns/influence.db and patterns/barriers.db. The details are
explained in *note Influential Patterns::.
File: gnugo.info, Node: Territory and Moyo, Next: Influence Usage, Prev: Influential Concepts, Up: Influence
13.2 Territory, Moyo and Area
=============================
Using the influence code, empty regions of the board are partitioned in
three ways. A vertex may be described as White or Black's "territory",
"moyo" or "area". The functions `whose_territory()', `whose_moyo()' and
`whose_area()' will return a color, or EMPTY if it belongs to one
player or the other in one of these classifications.
Those parts of the board which are expected to materialize as
actual points for one player or the other at the end of the
game are considered "territory".
Those parts of the board which are either already territory
or more generally places where a territory can easily
materialize if the opponent neglects to reduce are considered
Those parts of the board where one player or the other has a
stronger influence than his opponent are considered "area".
Generally territory is moyo and moyo is area. To get a feeling for
these concepts, load an sgf file in a middle game position with the
option `-m 0x0180' and examine the resulting diagrams (*note
File: gnugo.info, Node: Influence Usage, Next: Influence and Territory, Prev: Territory and Moyo, Up: Influence
13.3 Where influence gets used in the engine
============================================
The information obtained from the influence computation is used in a
variety of places in the engine, and the influence module is called
several times in the process of the move generation. The details of the
influence computation vary according to the needs of the calling
After GNU Go has decided about the tactical stability of strings, the
influence module gets called the first time. Here all lively stones act
as an influence source of default strength 100. The result is stored in
the variables `initial_influence' and `initial_opposite_influence', and
it is used as an important information for guessing the strength of
dragons. For example, a dragon that is part of a moyo of size 25 is
immediately considered alive. For dragons with a smaller moyo size, a
life-and-death analysis will be done by the owl code (see *note Pattern
Based Reading::). A dragon with a moyo size of only 5 will be
considered weak, even if the owl code has decided that it cannot be
As a tool for both the owl code and the strength estimate of dragons,
an "escape" influence gets computed for each dragon (*note Escape::).
Once all dragons have been evaluated, the influence module is called
again and the variables `initial_influence' and
`initial_opposite_influence' get overwritten. Of course, the dragon
status', which are available now, are taken into account. Stones
belonging to a dead dragon will not serve as an influence source, and
the strengths of other stones get adjusted according to the strength of
The result of this run is the most important tool for move
evaluation. All helper functions of patterns as explained in *note
Patterns:: that refer to influence results (e. g. `olib(*)' etc.)
actually use these results. Further, `initial_influence' serves as the
reference for computing the territorial value of a move. That is, from
the influence strengths stored in `initial_influence', a territory
value is assigned to each intersection. This value is supposed to
estimate the likelyhood that this intersection will become white or
Then, for each move that gets considered in the function
`value_moves', the influence module is called again via the function
`compute_move_influence' to assess the likely territorial balance after
this move, and the result is compared with the state before that move.
An additional influence computation is done in order to compute the
followup value of a move. Some explainations are in *note Territorial
Some of the public functions from `influence.c' which are used
throughout the engine are listed in *note Influence Utilities::.
File: gnugo.info, Node: Influence and Territory, Next: Territorial Details, Prev: Influence Usage, Up: Influence
13.4 Influence and Territory
============================
In this section we consider how the influence function is used to
estimate territory in the function `estimate_territorial_value()'.
A move like `*' by `O' below is worth one point:
This is evaluated by the influence function in the following way: We
first assign territory under the assumption that X moves first in all
local positions in the original position; then we reassing territory,
again under the assumption that `X' moves first in all local positions,
but after we let `O' make the move at `*'. These two territory
assignments are compared and the difference gives the territorial value
Technically, the assumption that `X' plays first everywhere is
implemented via an asymmetric pattern database in `barriers.db'. What
exactly is a safe connection that stops hostile influence from passing
through is different for `O' and `X'; of course such a connection has
to be tighter for stones with color `O'. Also, additional intrusion
influence sources are added for `X' in places where `X' stones have
In this specific example above, the asymmetry (before any move has
been made) would turn out as follows: If `X' is in turn to move, the
white influence would get stopped by a barrier at `*', leaving 4 points
of territory for `X'. However, if `O' was next to move, then a
followup move for the white stones at the left would be assumed in the
form of an extra ("intrusion") influence source at `*'. This would get
stopped at `a', leaving three points of territory.
Returning to the valuation of a move by `O' at `*', we get a value
of 1 for the move at `*'. However, of course this move is sente once
it is worth playing, and should therefore (in miai counting) be awarded
an effective value of 2. Hence we need to recognize the followup value
of a move. GNU Go 3.0 took care of this by using patterns in
`patterns.db' that enforced an explicit followup value. Versions from
3.2 on instead compute a seperate followup influence to each move
considered. In the above example, an intrusion source will be added at
`a' as a followup move to `*'. This destroys all of Black's territory
and hence gives a followup value of 3.
The pattern based followup value are still needed at some places,
To give another example, consider this position where we want to
estimate the value of an `O' move at `*':
Before the move we assume `X' moves first in the local position (and
that `O' has to connect), which gives territory like this (lower case
letter identify territory for each player):
Then we let `O' make the move at `*' and assume `X' moves first
again next. The territory then becomes (`X' is also assumed to have to
We see that this makes a difference in territory of 4, which is what
influence_delta_territory() should report. Then again, we have followup
value, and here also a reverse followup value. The reverse followup
value, which in this case will be so high that the move is treated as
reverse sente, is added by an explicit pattern. Other sources for
followup or reverse followup values are threats to capture a rescue a
string of stones. See the code and comments in the function
`value_move_reaons' for how followup and reverse followup values are
used to adjust the effective move value.
To give an example of territorial value where something is captured,
consider the `O' move at `*' here,
As before we first let the influence function determine territory
assuming X moves first, i.e. with a captured group:
Here `y' indicates `X' territory + captured stone, i.e. these count
for two points. After the `O' move at `*' we instead get
and we see that `X' has 16 territory fewer and `O' has two territory
more, for a total difference of 18 points.
That the influence function counts the value of captured stones was
introduced in GNU Go 3.2. Previously this was instead done using the
effective_size heuristic. The effective size is the number of stones
plus the surrounding empty spaces which are closer to this string or
dragon than to any other stones. Here the `O' string would thus have
effective size 6 (number of stones) + 2 (interior eye) + 2*0.5 (the two
empty vertices to the left of the string, split half each with the
surrounding X string) + 1*0.33 (the connection point, split between
three strings) = 9.33. As noted this value was doubled, giving 18.67
which is reasonably close to the correct value of 18. The effective size
heuristic is still used in certain parts of the move valuation where we
can't easily get a more accurate value from the influence function (e.
g. attacks depending on a ko, attack threats).
Note that this section only describes the territorial valuation of a
move. Apart from that, GNU Go uses various heuristics in assigning a
strategical value (weakening and strengthening of other stones on the
board) to a move. Also, the influence function isn't quite as well
tuned as the examples above may seem to claim. But it should give a
fairly good idea of how the design is intended.
Another matter is that so far we have only considered the change in
secure territory. GNU Go 3.2 and later versions use a revised
heuristic, which is explained in the next section, to assign probable
territory to each player.
File: gnugo.info, Node: Territorial Details, Next: The Influence Core, Prev: Influence and Territory, Up: Influence
13.5 Details of the Territory Valuation
=======================================
This section explains how GNU Go assigns a territorial value to an
intersection once the white and black influence have been computed.
The intention is that an intersection that has a chance of xx% of
becoming white territory is counted as 0.xx points of territory for
white, and similar for black.
The algorithm in the function `new_value_territory' goes roughly as
If `wi' is the white influence at a point, and `bi' the black
influence, then ` value = ( (wi-bi)/ (wi+bi) )^3' (positive values
indicates likley white territory, negative stand for black territory)
turns out to be very simple first guess that is still far off, but
reasonable enough to be useful.
This value is then suspect a number of corrections. Assume that this
first guess resulted in a positive value.
If both `bi' and `wi' are small, it gets reduced. What exactly is
"small" depends on whether the intersection is close to a corner or an
edge of the board, since it is easier to claim territory in the corner
Then the value at each intersection is degraded to the minimum value
of its neighbors. This can be seen as a second implementation of the
proverb saying that there is no territory in the center of the board.
This step substantially reduces the size of spheres of territory that
are open at several sides.
Finally, there are a number of patterns that explicitly forbid GNU
Go to count territory at some intersections. This is used e. g. for
false eyes that will eventually have to be filled in. Also, points for
To fine tune this scheme, some revisions have been made to the
influence computations that are relevant for territorial evaluation.
This includes a reduced default attenuation and some revised pattern
File: gnugo.info, Node: The Influence Core, Next: The Influence Algorithm, Prev: Territorial Details, Up: Influence
13.6 The Core of the Influence Function
=======================================
The basic influence radiation process can efficiently be implemented as
a breadth first search for adjacent and more distant points, using a
Influence barriers can be found by pattern matching, assisted by
reading through constraints and/or helpers. Wall structures, invasion
points and intrusion points can be found by pattern matching as well.
When influence is computed, the basic idea is that there are a number
of influence sources on the board, whose contributions are summed to
produce the influence values. For the time being we can assume that the
living stones on the board are the influence sources, although this is
The function `compute_influence()' contains a loop over the board,
and for each influence source on the board, the function
`accumulate_influence()' is called. This is the core of the influence
function. Before we get into the details, this is how the influence
field from a single isolated influence source of strength 100 turns out
(with an attenuation of 3.0):
0 1 3 11 33 X 33 11 3 1 0
These values are in reality floating point numbers but have been
rounded down to the nearest integer for presentation. This means that
the influence field does not stop when the numbers become zeroes.
Internally `accumulate_influence()' starts at the influence source
and spreads influence outwards by means of a breadth first propagation,
implemented in the form of a queue. The order of propagation and the
condition that influence only is spread outwards guarantee that no
intersection is visited more than once and that the process terminates.
In the example above, the intersections are visited in the following
+ 78 68 66 64 63 65 67 69 79 +
+ 62 46 38 36 35 37 39 47 75 +
+ 60 34 22 16 15 17 23 43 73 +
+ 58 32 14 6 3 7 19 41 71 +
+ 56 30 12 2 0 4 18 40 70 +
+ 57 31 13 5 1 8 20 42 72 +
+ 59 33 21 10 9 11 24 44 74 +
+ 61 45 28 26 25 27 29 48 76 +
+ 77 54 52 50 49 51 53 55 80 +
The visitation of intersections continues in the same way on the
intersections marked '`+' and further outwards. In a real position
there will be stones and tight connections stopping the influence from
spreading to certain intersections. This will disrupt the diagram
above, but the main property of the propagation still remains, i.e. no
intersection is visited more than once and after being visited no more
influence will be propagated to the intersection.
File: gnugo.info, Node: The Influence Algorithm, Next: Permeability, Prev: The Influence Core, Up: Influence
13.7 The Influence Algorithm
============================
Let `(m, n)' be the coordinates of the influence source and `(i, j)'
the coordinates of a an intersection being visited during propagation,
using the same notation as in the `accumulate_influence()' function.
Influence is now propagated to its eight closest neighbors, including
the diagonal ones, according to the follow scheme:
For each of the eight directions `(di, dj)', do:
1. Compute the scalar product `di*(i-m) + dj*(j-n)' between the
vectors `(di,dj)' and `(i,j) - (m,n)'
2. If this is negative or zero, the direction is not outwards and we
continue with the next direction. The exception is when we are
visiting the influence source, i.e. the first intersection, when
we spread influence in all directions anyway.
3. If `(i+di, j+dj)' is outside the board or occupied we also
continue with the next direction.
4. Let S be the strength of the influence at `(i, j)'. The influence
propagated to `(i+di, j+dj)' from this intersection is given by
`P*(1/A)*D*S', where the three different kinds of damping are:
* The permeability `P', which is a property of the board
intersections. Normally this is one, i.e. unrestricted
propagation, but to stop propagation through e.g. one step
jumps, the permeability is set to zero at such intersections
through pattern matching. This is further discussed below.
* The attenuation `A', which is a property of the influence
source and different in different directions. By default this
has the value 3 except diagonally where the number is twice
as much. By modifying the attenuation value it is possible to
obtain influence sources with a larger or a smaller effective
* The directional damping `D', which is the squared cosine of
the angle between `(di,dj)' and `(i,j) - (m,n)'. The idea is
to stop influence from "bending" around an interfering stone
and get a continuous behavior at the right angle cutoff. The
choice of the squared cosine for this purpose is rather
arbitrary, but has the advantage that it can be expressed as a
rational function of `m', `n', `i', `j', `di', and `dj',
without involving any trigonometric or square root
computations. When we are visiting the influence source we
let by convention this factor be one.
Influence is typically contributed from up to three neighbors
"between" this intersection and the influence source. These values are
simply added together. As pointed out before, all contributions will
automatically have been made before the intersection itself is visited.
When the total influence for the whole board is computed by
`compute_influence()', `accumulate_influence()' is called once for each
influence source. These invocations are totally independent and the
influence contributions from the different sources are added together.
File: gnugo.info, Node: Permeability, Next: Escape, Prev: The Influence Algorithm, Up: Influence
The permeability at the different points is initially one at all empty
intersections and zero at occupied intersections. To get a useful
influence function we need to modify this, however. Consider the
|...a.X ('a' empty intersection)
The corner is of course secure territory for `O' and clearly the `X'
stone has negligible effect inside this position. To stop `X' influence
from leaking into the corner we use pattern matching (pattern
Barrier1/Barrier2 in `barriers.db') to modify the permeability for `X'
at this intersection to zero. `O' can still spread influence through
Another case that needs to be mentioned is how the permeability
damping is computed for diagonal influence radiation. For horizontal
and vertical radiation we just use the permeability (for the relevant
color) at the intersection we are radiating from. In the diagonal case
we additionally multiply with the maximum permeability at the two
intersections we are trying to squeeze between. The reason for this can
be found in the diagram below:
We don't want `X' influence to be spread from `a' to `b', and since
the permeability at both c and d is zero, the rule above stops this.
File: gnugo.info, Node: Escape, Next: Break Ins, Prev: Permeability, Up: Influence
One application of the influence code is in computing the
`dragon.escape_route' field. This is computed by the function
`compute_escape()' as follows. First, every intersection is assigned
an escape value, ranging between 0 and 4, depending on the influence
value of the opposite color.
The `escape_route' field is modified by the code in `surround.c'
(*note Surrounded Dragons::). It is divided by two for weakly surrounded
dragons, and set to zero for surrounded ones.
In addition to assiging an escape value to empty vertices, we also
assign an escape value to friendly dragons. This value can range from 0
to 6 depending on the status of the dragon, with live dragons having
Then we sum the values of the resulting influence escape values over
the intersections (including friendly dragons) at distance 4, that is,
over those intersections which can be joined to the dragon by a path of
length 4 (and no shorter path) not passing adjacent to any unfriendly
dragon. In the following example, we sum the influence escape value
over the four vertices labelled '4'.
. . . . . . . . . . . . . . . . . .
. . . . . X . . O . . . . . X . . O
. . X . . . . . O . . X . 2 . 4 . O
X . . . . . . . . X . . 1 1 2 3 4 .
X O . O . . . . O X O 1 O 1 2 3 4 O
X O . O . . . . . X O 1 O 1 . 4 . .
X O . . . X . O O X O 1 . . X . . O
. . . X . . . . . . 1 . X . . . . .
X . . . . X . . . X . . . . X . . .
. . . . . . . . . . . . . . . . . .
Since the dragon is trying to reach safety, the reader might wonder
why `compute_influence()' is called with the opposite color of the
dragon contemplating escape. To explain this point, we first remind
the reader why there is a color parameter to `compute_influence()'.
Consider the following example position:
Whether the bottom will become O territory depends on who is in turn
to play. This is implemented with the help of patterns in barriers.db,
so that X influence is allowed to leak into the bottom if X is in turn
to move but not if O is. There are also "invade" patterns which add
influence sources in sufficiently open parts of the board which are
handled differently depending on who is in turn to move.
In order to decide the territorial value of an O move in the third
line gap above, influence is first computed in the original position
with the opponent (i.e. X) in turn to move. Then the O stone is played
Now influence is computed once more, also this time with X in turn to
move. The difference in territory (as computed from the influence
values) gives the territorial value of the move.
Exactly how influence is computed for use in the escape route
estimation is all ad hoc. But it makes sense to assume the opponent
color in turn to move so that the escape possibilities aren't
overestimated. After we have made a move in the escape direction it is
after all the opponent's turn.
The current escape route mechanism seems good enough to be useful
but is not completely reliable. Mostly it seems to err on the side of
File: gnugo.info, Node: Break Ins, Next: Surrounded Dragons, Prev: Escape, Up: Influence
The code in `breakin.c' break-ins into territories that require deeper
tactical reading and are thus impossible to detect for the influence
module. It gets run after the influence module and revises its
The break-in code makes use of two public functions in
* int break_in(int str, const char goal[BOARDMAX], int *move)
Returns WIN if `str' can connect to the area `goal[]' (which
may or may not contain stones), if the string's owner gets
* int block_off(int str, const char goal[BOARDMAX], int *move)
Returns WIN if `str' cannot connect to the area `goal[]'
(which may or may not contain stones), if the other color
These functions are public front ends to their counterparts
`recursive_break_in' and `recursive_block_off', which call each other
The procedure is as follows: We look at all big (>= 10) territory
regions as detected by the influence code. Using the computation of
connection distances from readconnect.c, we compute all nearby vertices
of this territory. We look for the closest safe stones belonging to the
For each such string `str' we call
* `break_in(str, territory)' if the opponent is assumed to be next
* `block_off(str, territory)' if the territory owner is next.
If the break in is successful resp. the blocking unsuccessful, we
shrink the territory, and see whether the opponent can still break in.
We repeat this until the territory is shrunk so much that the opponent
To see the break in code in action run GNU Go on the file
`regression/games/break_in.sgf' with the option `-d0x102000'. Among the
Trying to break in from D7 to:
E9 (1) F9 (1) G9 (1) E8 (1) F8 (1) G8 (1)
H8 (1) G7 (1) H7 (1) J7 (1) H6 (1) J6 (1)
H5 (1) J5 (1) H4 (1) J4 (1) H3 (1) J3 (1)
block_off D7, result 0 PASS (355, 41952 nodes, 0.73 seconds)
E9 (1) F9 (1) G9 (1) E8 (1) F8 (1) G8 (1)
H8 (1) G7 (1) H7 (1) J7 (1) H6 (1) J6 (1)
H5 (1) J5 (1) H4 (1) J4 (1) H3 (1) J3 (1)
Erasing territory at E8 -b.
Erasing territory at G3 -b.
Now trying to break to smaller goal:
F9 (1) G9 (1) F8 (1) G8 (1) H8 (1) G7 (1)
H7 (1) J7 (1) H6 (1) J6 (1) H5 (1) J5 (1)
H4 (1) J4 (1) H3 (1) J3 (1) H2 (1) J2 (1)
This means that the function `break_in' is called with the goal
marked 'a' in the following diagram. The code attempts to find out
whether it is possible to connect into this area from the string at
A breakin is found, so the goal is shrunk by removing `E9' and `J2',
then break_in is called again.
In order to see what reading is actually done in order to do this
break in, you may load GNU Go in gtp mode, then issue the commands:
break_in D7 E9 F9 G9 E8 F8 G8 H8 G7 H7 J7 H6 J6 H5 J5 H4 J4 H3 J3 H2 J2
break_in D7 F9 G9 F8 G8 H8 G7 H7 J7 H6 J6 H5 J5 H4 J4 H3 J3 H2 J2
finish_sgftrace vars1.sgf
This will produce two sgf files containing the variations caused by
these calls to the breakin code. The second file, `vars1.sgf' will
contain quite a few variations.
The break in code makes a list of break ins which are found. When
it is finished, the function `add_expand_territory_move' is called for
each break in, adding a move reason.
The break in code is slow, and only changes a few moves by the engine
per game. Nevertheless we believe that it contributes substantially to
the strength of the program. The break in code is enabled by default in
GNU Go 3.6 at level 10, and disabled at level 9. In fact, this is the
*only* difference between levels 9 and 10 in GNU Go 3.6.
File: gnugo.info, Node: Surrounded Dragons, Next: Influential Patterns, Prev: Break Ins, Up: Influence
When is a dragon surrounded?
As has been pointed out by Bruce Wilcox, the geometric lines
connecting groups of the opposite color are often important. It is very
hard to prevent the escape of this `O' dragon:
On the other hand, this dragon is in grave danger:
The difference between these two positions is that in the first, the
`O' dragon crosses the line connecting the top two `X' stones.
Code in `surround.c' implements a test for when a dragon is
surrounded. The idea is to compute the convex hull of the _surround
set_, that is, the set stones belonging to unfriendly neighbor dragons.
If the dragon is contained within that hull. If it is, it is said to be
In practice this scheme is modified slightly. The implementation
uses various algorithms to compute distances and hostile stones are
discarded from the surround set when a pair other hostile ones can be
found which makes the considered one useless. For example, in the
following position the bottom `O' stone would get discarded.
Also, points are added to the surround set below stones on the
second and third lines. This should account for the edge being a
In order to compute distances between corners of the convex hull a
sorting by angle algorithm has been implemented. If the distance
between a pair enclosing stones is large, the surround status gets
decreased to `WEAKLY_SURROUNDED', or even 0 for very large ones.
The sorting by angle must be explained. A small diagram will
The sorting algorithm will generate this:
That is, the points are sorted by ascending order of the measure of
the angle S-G-O, where S is SOUTH, G the (approximated) gravity center
of the goal, and O the position of the considered hostile stones.
The necessity of such sorting appears when one tries to measure
distances between enclosing stones without sorting them, just by using
directly the existing left and right corners arrays. In some positions,
the results will be inconsistent. Imagine, for example a position where
for instance the points 1,2,3,4,6 and 7 were in the left arrary,
leaving only 5 and 8 in the right array. Because of the large distance
between 5 and 8, the dragon would have declared weak surrounded or not
surrounded at all. Such cases are rare but frequent enough to require
This is "more" surrounded than the following position:
In the second case, the surround status would be lowered to
The surround code is used to modify the escape_route field in the
dragon2 data array. When a dragon is WEAKLY_SURROUNDED, the
escape_route is divided by 2. If the dragon is SURROUNDED, escape_route
File: gnugo.info, Node: Influential Patterns, Next: Influential Display, Prev: Surrounded Dragons, Up: Influence
13.12 Patterns used by the Influence module
===========================================
This section explains the details of the pattern databases used for the
First, we have the patterns in `influence.db', which get matched
symmetrically for both colors.
These patterns add extra influence sources close to some
shapes like walls. This tries to reflect their extra
strength. These patterns are not used in the influence
computations relevant for territory valuations, but they are
useful for getting a better estimate of strengths of groups.
These patterns add extra influence sources at typical
invasion points. Usually they are of small strength. If they
additionally have the class `s', the extra influence source
is added for both colors. Otherwise, only the player assumed
to be next to move gets the benefit.
The patterns in `barriers.db' get matched only for `O' being the
Connections between `X' stones that stop influence of `O'.
They have to be tight enough that `O' cannot break through,
even though he is allowed to move first.
Connections between `O' stones that stop influence of `X'. The
stones involved can be more loosely connected than those in
These indicate positions of followup moves for the `O' stone
marked with `Q' in the pattern. They are used to reduce the
territory e. g. where a monkey jump is possible. Also, they
are used in the computation of the followup influence, if the
`Q' stone was the move played (or a stone saved by the move
These patterns indicate intersections where one color will
not be able to get territory, for example in a false eye. The
points are set with a call to the helper non_oterritory or
non_xterritory in the action of the pattern.
The intrusion patterns (`B') are more powerful than the description
above might suggest. They can be very helpful in identifying weak shapes
(by adding an intrusion source for the opponent where he can break
through). A negative inference for this is that a single bad `B'
pattern, e. g. one that has a wrong constraint, typically causes 5 to
10 `FAIL's in the regression test suite.
Influence Patterns can have autohelper constraints as usual. As for
the constraint attributes, there are (additionally to the usual ones
`O', `o', `X' and `x'), attributes `Y' and `FY'. A pattern marked with
`Y' will only be used in the influence computations relevant for the
territory valuation, while `FY' patterns only get used in the other
The action of an influence pattern is at the moment only used for
non-territory patterns as mentioned above, and as a workaround for a
problem with `B' patterns in the followup influence.
To see why this workaround is necessary, consider the follwoing
(Imagine that there is `X' territory on the left.)
The move by `O' at `*' has a natural followup move at `a'. So, in
the computation of the followup influence for `*', there would be an
extra influence source for `O' at `a' which would destroy a lot of
black territory on the left. This would give a big followup value, and
in effect the move `*' would be treated as sente.
But of course it is gote, since `X' will answer at `a', which both
stops the possible intrusion and threatens to capture `*'. This
situation is in fact quite common.
Hence we need an additional constraint that can tell when an
intrusion pattern can be used in followup influence. This is done by
misusing the action line: An additional line
gets added to the pattern. The `condition' should be true if the
intrusion cannot be stopped in sente. In the above example, the relevant
intrusion pattern will have an action line of the form
>return (!xplay_attack(a,b));
where `b' refers to the stone at `*'. In fact, almost all
followup-specific constraints look similar to this.
File: gnugo.info, Node: Influential Display, Next: Influence Tuning, Prev: Influential Patterns, Up: Influence
13.13 Colored display and debugging of influence
================================================
There are various ways to obtain detailed information about the
influence computations. Colored diagrams showing influence are possible
from a colored xterm or rxvt window.
There are two options controlling when to generate diagrams:
Show diagrams for the initial influence computation. This is
done twice, the first time before `make_dragons()' is run and
the second time after. The difference is that dead dragons
are taken into account the second time. Tactically captured
worms are taken into account both times.
* `--debug-influence LOCATION'
Show influence diagrams after the move at the given location.
An important limitation of this option is that it's only
effective for moves that the move generation is considering.
The other options control which diagrams should be generated in these
situations. You have to specify at least one of the options above and
at least one of the options below to generate any output.
* The options below must be combined with one of the two previous
ones, or the diagram will not be printed. For example to print the
influence diagram, you may combine 0x08 and 0x010, and use the option
Show colored display of territory/moyo/area regions.
This feature is very useful to get an immediate impression of
the influence regions as GNU Go sees them.
Show numerical influence values for white and black. These
come in two separate diagrams, the first one for white, the
second one for black. Notice that the influence values are
represented by floats and thus have been rounded in these
This generates two diagrams showing the permeability for
black and white influence on the board.
This shows the strength of the influence sources for black
and white across the board. You will see sources at each
lively stone (with strength depending on the strength of this
stone), and sources contributed by patterns.
This shows the attenuation with which the influence sources
spread influence across the board. Low attenuation indicates
far-reaching influence sources.
This shows the territory valuation of GNU Go. Each
intersection is shown with a value between -1.0 and +1.0 (or
-2 resp. +2 if there is a dead stone on this intersection).
Positive values indicate territory for white. A value of -0.5
thus indicates a point where black has a 50% chance of
Finally, there is the debug option `-d 0x1' which turns on on
`DEBUG_INFLUENCE'. This gives a message for each influence pattern that
gets matched. Unfortunately, these are way too many messages making it
tedious to navigate the output. However, if you discover an influence
source with `-m 0x80' that looks wrong, the debug output can help you
to quickly find out the responsible pattern.
File: gnugo.info, Node: Influence Tuning, Prev: Influential Display, Up: Influence
13.14 Influence Tuning with `view.pike'
=======================================
A useful program in the regression directory is `view.pike'. To run
it, you need Pike, which you may download from
`http://pike.ida.liu.se/'.
The test case `endgame:920' fails in GNU Go 3.6. We will explain how
Start by firing up view.pike on testcase endgame:920, e.g. by running
`pike view.pike endgame:920' in the regression directory.
We see from the first view of move values that filling dame at P15 is
valued highest with 0.17 points while the correct move at C4 is valued
slightly lower with 0.16. The real problem is of course that C4 is
worth a full point and thus should be valued about 1.0.
Now click on C4 to get a list of move reasons and move valuation
information. Everything looks okay except that change in territory is
0.00 rather than 1.00 as it ought to be.
We can confirm this by choosing the "delta territory for..." button
and again clicking C4. Now B5 should have been marked as one point of
change in territory, but it's not.
Next step is to enter the influence debug tool. Press the "influence"
button, followed by "black influence, dragons known," and "territory
value." This shows the expected territory if black locally moves first
everywhere (thus "black influence"). Here we can see that B5 is
incorrectly considered as 1.0 points of white territory.
We can compare this with the territory after a white move at C4
(still assuming that black locally moves first everywhere after that) by
pressing "after move influence for..." and clicking C4. This looks
identical, as expected since delta territory was 0, but here it is
correct that B5 is 1.0 points of territory for white.
The most straightforward solution to this problem is to add a
non-territory pattern, saying that white can't get territory on B5 if
black moves first. The nonterritory patterns are in `barriers.db'.
In these patterns it's always assumed that `O' moves first and thus
it says that `X' can't get territory at `B5' (`e' in the pattern). Now
we need to be a bit careful however since after `O' plays at `a' and
`X' cuts in at `b', it may well happen that `O' needs to defend around
`d', allowing `X' to cut at `c', possibly making the nonterritory
assumption invalid. It's difficult to do this entirely accurate, but
the constraint above is fairly conservative and should guarantee that
`a' is safe in most, although not all, cases.
File: gnugo.info, Node: Monte Carlo Go, Next: Libboard, Prev: Influence, Up: Top
In Monte Carlo Go the engine plays random games to the end, generating
moves from a pattern database within the context of the algorithm UCT
(upper confidence bounds applied to trees). This algorithm allowed the
program MoGo (`http://www.lri.fr/~gelly/MoGo.htm', to become the first
computer program to defeat a professional while taking a 9 stone
handicap (`http://senseis.xmp.net/?MoGo').
GNU Go 3.8 can play 9x9 Go with the option `--monte-carlo' using the
UCT algorithm. For command line options, see *Note Invoking GNU Go::.
During reading, the engine makes incremental updates of local 3x3
neighborhood, suicide status, self-atari status, and number of stones
GNU Go's simulations (Monte Carlo games) are pattern generated. The
random playout move generation is distributed strictly proportional to
move values computed by table lookup from a local context consisting of
3x3 neighborhood, opponent suicide status, own and opponent self-atari
status, number of stones captured by own and opponent move, and
closeness to the previous move. Let's call this local context simply "a
pattern" and the table "pattern values" or simply "patterns".
There are three built-in databases that you can select using the
option `--mc-patterns <name>', where `<name>' is one of
The first of these is an approximation of the previous random move
generation algorithm. The `mogo_classic' pattern values is an
approximation of the simulation policy used by early versions of MoGo,
as published in the report odification of UCT with Patterns in
Monte-Carlo Go (http://hal.inria.fr/inria-00117266) RR-6062, by Sylvain
Gelly, Yizao Wang, Rémi Munos, and Olivier Teytaud. The uniform pattern
values is the so called "light" playout which chooses uniformly between
all legal moves except single point proper eyes.
If you're not satisfied with these you can also tune your own
pattern values with a pattern database file and load it at runtime with
`--mc-load-patterns <name>' adding your own pattern database.
Let's start with the uniform pattern values. Those are defined by the
file `patterns/mc_uniform.db', which looks like this:
Patterns are always exactly 3x3 in size with the move at the center
point. The symbols are the usual for GNU Go pattern databases:
O own stone (i.e. the same color as the color to move)
x opponent stone or empty
? own stone, opponent stone, or empty
There's also a new symbol:
% own stone, opponent stone, empty, or edge
After the pattern comes a line starting with a colon. In all these
patterns it says that the pattern has a move value of 0, i.e. must not
be played. Unmatched patterns have a default value of 1. When all move
values are zero for both players, the playout will stop. Including the
three patterns above is important because otherwise the playouts would
be likely to go on indefinitely, or as it actually happens be
terminated at a hard-coded limit of 600 moves. Also place these
patterns at the top of the database because when multiple patterns
match, the first one is used, regardless of the values.
When using only these patterns you will probably notice that it plays
rather heavy, trying hard to be solidly connected. This is because
uniform playouts are badly biased with a high probability of non-solid
connections being cut apart. To counter this you could try a pattern
to increase the probability that the one-point jump is reinforced
when threatened. Here we added the property "near", which means that the
pattern only applies if the previous move was played "near" this move.
Primarily "near" means within the surrounding 3x3 neighborhood but it
also includes certain cases of liberties of low-liberty strings
adjacent to the previous move, e.g. the move to extend out of an atari
created by the previous move. You have to read the source to find out
the exact rules for nearness.
We could also be even more specific and say
to exclude the cases where this move is a self atari (osafe) or would
be a self-atari for the opponent (xsafe).
It may also be interesting to see the effect of capturing stones. A
catch-all pattern for captures would be
where we have used multiple colon lines to specify different move
values depending on the number of captured stones; value 10 for a
single captured stone, value 20 for two captured stones, and value 30
for three or more captured stones. Here we also excluded self-atari
moves in the case of 1 captured stone in order to avoid getting stuck
in triple-ko in the playouts (there's no superko detection in the
The full set of pattern properties is as follows:
The move is "near" the previous move.
The move is not "near" the previous move.
The move is not a self-atari.
The move is a self-atari.
The move would not be a self-atari for the opponent.
The move would be a self-atari for the opponent.
The move would be suicide for the opponent
The move would not be suicide for the opponent.
The move captures zero stones.
The move captures one stone.
The move captures two stones.
The move captures three or more stones.
The move captures one or more stones.
The move captures at most one stone.
The move captures two or more stones.
The move captures at most two stones.
An opponent move would capture zero stones.
An opponent move would capture one stone.
An opponent move would capture two stones.
An opponent move would capture three or more stones.
An opponent move would capture one or more stones.
An opponent move would capture at most one stone.
An opponent move would capture two or more stones.
An opponent move would capture at most two stones.
These can be combined arbitrarily but all must be satisfied for the
pattern to take effect. If contradictory properties are combined, the
pattern will never match.
* Move values are unsigned 32-bit integers. To avoid overflow in
computations it is highly recommended to keep the values below
* There is no speed penalty for having lots of patterns in the
database. The average time per move is approximately constant
(slightly dependent on how often stones are captured or become low
on liberties) and the time per game mostly depends on the average
* For more complex pattern databases, see
`patterns/mc_montegnu_classic.db' and
`patterns/mc_mogo_classic.db'.
Nobody really knows how to tune the random playouts to get as strong
engine as possible. Please play with this and report any interesting
findings, especially if you're able to make it substantially stronger
than the `montegnu_classic' patterns.
File: gnugo.info, Node: Libboard, Next: SGF, Prev: Monte Carlo Go, Up: Top
* Board Data Structures:: Board Data Structures
* The Board Array:: One-dimensional board array
* Incremental Board:: Incremental board data structures
* Some Board Functions:: Explanation of some board functions
The foundation of the GNU Go engine is a library of very efficient
routines for handling go boards. This board library, called
`libboard', can be used for those programs that only need a basic go
board but no AI capability. One such program is `patterns/joseki.c',
which compiles joseki pattern databases from SGF files.
If you want to use the board library in your own program, you need
all the .c-files listed under libboard_SOURCES in engine/Makefile.am,
and the files in the directories sgf/ and utils/. Then you should
include engine/board.h in your code.
The library consists of the following files:
The public interface to the board library.
The basic board code. It uses incremental algorithms for
keeping track of strings and liberties on the go board.
This contains all global variable of the board library.
Code for hashing go positions.
Implementation of output file in SGF format.
Utilities for printing go boards and other things.
To use the board library, you must include `liberty.h' just like
when you use the whole engine, but of course you cannot use all the
functions declared in it, i.e. the functions that are part of the
engine, but not part of the board library. You must link your
application with `libboard.a'.
File: gnugo.info, Node: Board Data Structures, Next: The Board Array, Up: Libboard
15.1 Board Data structures
==========================
The basic data structures of the board correspond tightly to the
`board_state' struct described in *Note The Board State::. They are all
stored in global variables for efficiency reasons, the most important
Intersection board[MAXSIZE];
The description of the `Position' struct is applicable to these
variables also, so we won't duplicate it here. All these variables are
globals for performance reasons. Behind these variables, there are a
number of other private data structures. These implement incremental
handling of strings, liberties and other properties (*note Incremental
Board::). The variable `hashdata' contains information about the hash
value for the current position (*note Hashing::).
These variables should never be manipulated directly, since they are
only the front end for the incremental machinery. They can be read, but
should only be written by using the functions described in the next
section. If you write directly to them, the incremental data structures
will become out of sync with each other, and a crash is the likely
File: gnugo.info, Node: The Board Array, Next: Incremental Board, Prev: Board Data Structures, Up: Libboard
GNU Go represents the board in a one-dimensional array called `board'.
For some purposes a two dimensional indexing of the board by parameters
The `board' array includes out-of-board markers around the board. To
make the relation to the old two-dimensional board representation
clear, this figure shows how the 1D indices correspond to the 2D
indices when MAX_BOARD is 7.
i +----------------------------------
1| 16 17 18 19 20 21 22 23
2| 24 25 26 27 28 29 30 31
3| 32 33 34 35 36 37 38 39
4| 40 41 42 43 44 45 46 47
5| 48 49 50 51 52 53 54 55
6| 56 57 58 59 60 61 62 63
7| 64 65 66 67 68 69 70 71 72
To convert between a 1D index `pos' and a 2D index `(i,j)', the
macros `POS', `I', and `J' are provided, defined as below:
#define POS(i, j) ((MAX_BOARD + 2) + (i) * (MAX_BOARD + 1) + (j))
#define I(pos) ((pos) / (MAX_BOARD + 1) - 1)
#define J(pos) ((pos) % (MAX_BOARD + 1) - 1)
All 1D indices not corresponding to points on the board have the out
of board marker value `GRAY'. Thus if `board_size' and `MAX_BOARD' both
i +----------------------------------
The indices marked `#' have value `GRAY'. If `MAX_BOARD' is 7 and
i +----------------------------------
Navigation on the board is done by the `SOUTH', `WEST', `NORTH', and
#define NS (MAX_BOARD + 1)
#define SOUTH(pos) ((pos) + NS)
#define WEST(pos) ((pos) - 1)
#define NORTH(pos) ((pos) - NS)
#define EAST(pos) ((pos) + 1)
There are also shorthand macros `SW', `NW', `NE', `SE', `SS', `WW',
`NN', `EE' for two step movements.
Any movement from a point on the board to an adjacent or diagonal
vertex is guaranteed to produce a valid index into the board array, and
the color found is GRAY if it is not on the board. To do explicit tests
for out of board there are two macros
#define ON_BOARD(pos) (board[pos] != GRAY)
#define ON_BOARD1(pos) (((unsigned) (pos) < BOARDSIZE) && board[pos] != GRAY)
where the first one should be used in the algorithms and the second
one is useful for assertion tests.
The advantage of a one-dimensional board array is that it gives a
significant performance advantage. We need only one variable to
determine a board position, which means that many functions need less
arguments. Also, often one computation is sufficient for 1D-coordinate
where we would need two with two 2D-coordinates: If we, for example,
want to have the coordinate of the upper right of `pos', we can do this
with `NORTH(EAST(pos))' instead of `(i+1, j-1)'.
*Important*: The 2D coordinate `(-1,-1)', which is used for pass and
sometimes to indicate no point, maps to the 1D coordinate `0', not to
`-1'. Instead of a plain `0', use one of the macros `NO_MOVE' or
A loop over multiple directions is straightforwardly written:
for (k = 0; k < 4; k++) {
The following constants are useful for loops over the entire board
and allocation of arrays with a 1-1 mapping to the board.
#define BOARDSIZE ((MAX_BOARD + 2) * (MAX_BOARD + 1) + 1)
#define BOARDMIN (MAX_BOARD + 2)
#define BOARDMAX (MAX_BOARD + 1) * (MAX_BOARD + 1)
`BOARDSIZE' is the actual size of the 1D board array, `BOARDMIN' is
the first index corresponding to a point on the board, and `BOARDMAX'
is one larger than the last index corresponding to a point on the board.
Often one wants to traverse the board, carrying out some function at
every vertex. Here are two possible ways of doing this:
for (m = 0; m < board_size; m++)
for (n = 0; n < board_size; n++) {
for (pos = BOARDMIN; pos < BOARDMAX; pos++) {
File: gnugo.info, Node: Incremental Board, Next: Some Board Functions, Prev: The Board Array, Up: Libboard
15.3 Incremental Board data structures
======================================
In addition to the global board state, the algorithms in `board.c'
implement a method of incremental updates that keeps track of the
following information for each string:
* The color of the string.
* Number of stones in the string.
* Origin of the string, i.e. a canonical reference point, defined to
be the stone with smallest 1D board coordinate.
* A list of the stones in the string.
* A list of the liberties. If there are too many liberties the list
* The number of neighbor strings.
* A list of the neighbor strings.
The basic data structure is
int color; /* Color of string, BLACK or WHITE */
int size; /* Number of stones in string. */
int origin; /* Coordinates of "origin", i.e. */
/* "upper left" stone. */
int liberties; /* Number of liberties. */
int libs[MAX_LIBERTIES]; /* Coordinates of liberties. */
int neighbors; /* Number of neighbor strings */
int neighborlist[MAXCHAIN]; /* List of neighbor string numbers. */
int mark; /* General purpose mark. */
struct string_data string[MAX_STRINGS];
It should be clear that almost all information is stored in the
`string' array. To get a mapping from the board coordinates to the
static int string_number[BOARDMAX];
which contains indices into the `string' array. This information is only
valid at nonempty vertices, however, so it is necessary to first verify
that `board[pos] != EMPTY'.
The `string_data' structure does not include an array of the stone
coordinates. This information is stored in a separate array:
static int next_stone[BOARDMAX];
This array implements cyclic linked lists of stones. Each vertex
contains a pointer to another (possibly the same) vertex. Starting at
an arbitrary stone on the board, following these pointers should
traverse the entire string in an arbitrary order before coming back to
the starting point. As for the 'string_number' array, this information
is invalid at empty points on the board. This data structure has the
good properties of requiring fixed space (regardless of the number of
strings) and making it easy to add a new stone or join two strings.
Additionally the code makes use of some work variables:
static int strings_initialized = 0;
The `ml' array and `liberty_mark' are used to "mark" liberties on
the board, e.g. to avoid counting the same liberty twice. The
convention is that if `ml[pos]' has the same value as `liberty_mark',
then `pos' is marked. To clear all marks it suffices to increase the
value of `liberty_mark', since it is never allowed to decrease.
The same relation holds between the `mark' field of the `string_data'
structure and `string_mark'. Of course these are used for marking
`next_string' gives the number of the next available entry in the
`string' array. Then `strings_initialized' is set to one when all data
structures are known to be up to date. Given an arbitrary board
position in the `board' array, this is done by calling
`incremental_board_init()'. It is not necessary to call this function
explicitly since any other function that needs the information does
this if it has not been done.
The interesting part of the code is the incremental update of the
data structures when a stone is played and subsequently removed. To
understand the strategies involved in adding a stone it is necessary to
first know how undoing a move works. The idea is that as soon as some
piece of information is about to be changed, the old value is pushed
onto a stack which stores the value and its address. The stack is built
from the following structures:
struct change_stack_entry {
struct change_stack_entry change_stack[STACK_SIZE];
and manipulated with the macros
Calling `BEGIN_CHANGE_RECORD()' stores a null pointer in the address
field to indicate the start of changes for a new move. As mentioned
earlier `PUSH_VALUE()' stores a value and its corresponding address.
Assuming that all changed information has been duly pushed onto the
stack, undoing the move is only a matter of calling `POP_MOVE()', which
simply assigns the values to the addresses in the reverse order until
the null pointer is reached. This description is slightly simplified
because this stack can only store 'int' values and we need to also
store changes to the board. Thus we have two parallel stacks where one
stores `int' values and the other one stores `Intersection' values.
When a new stone is played on the board, first captured opponent
strings, if any, are removed. In this step we have to push the board
values and the `next_stone' pointers for the removed stones, and update
the liberties and neighbor lists for the neighbors of the removed
strings. We do not have to push all information in the 'string' entries
of the removed strings however. As we do not reuse the entries they
will remain intact until the move is pushed and they are back in use.
After this we put down the new stone and get three distinct cases:
1. The new stone is isolated, i.e. it has no friendly neighbor.
2. The new stone has exactly one friendly neighbor.
3. The new stone has at least two friendly neighbors.
The first case is easiest. Then we create a new string by using the
number given by `next_string' and increasing this variable. The string
will have size one, `next_stone' points directly back on itself, the
liberties can be found by looking for empty points in the four
directions, possible neighbor strings are found in the same way, and
those need also to remove one liberty and add one neighbor.
In the second case we do not create a new string but extend the
neighbor with the new stone. This involves linking the new stone into
the cyclic chain, if needed moving the origin, and updating liberties
and neighbors. Liberty and neighbor information also needs updating for
the neighbors of the new stone.
In the third case finally, we need to join already existing strings.
In order not to have to store excessive amounts of information, we
create a new string for the new stone and let it assimilate the
neighbor strings. Thus all information about those can simply be left
around in the 'string' array, exactly as for removed strings. Here it
becomes a little more complex to keep track of liberties and neighbors
since those may have been shared by more than one of the joined
strings. Making good use of marks it all becomes rather straightforward
The often used construction
} while (!BACK_TO_FIRST_STONE(s, pos));
traverses the stones of the string with number `s' exactly once, with
`pos' holding the coordinates. In general `pos' is used as board
coordinate and `s' as an index into the `string' array or sometimes a
pointer to an entry in the `string' array.
File: gnugo.info, Node: Some Board Functions, Prev: Incremental Board, Up: Libboard
15.4 Some Board Functions
=========================
*Reading*, often called *search* in computer game theory, is a
fundamental process in GNU Go. This is the process of generating
hypothetical future boards in order to determine the answer to some
question, for example "can these stones live." Since these are
hypothetical future positions, it is important to be able to undo them,
ultimately returning to the present board. Thus a move stack is
maintained during reading. When a move is tried, by the function
`trymove', or its variant `tryko'. This function pushes the current
board on the stack and plays a move. The stack pointer `stackp', which
keeps track of the position, is incremented. The function `popgo()'
pops the move stack, decrementing `stackp' and undoing the last move
Every successful `trymove()' must be matched with a `popgo()'. Thus
the correct way of using this function is:
if (trymove(pos, color, ... )) {
... [potentially lots of code here]
In case the move is a ko capture, the legality of the capture is
subject to the komaster scheme (*note Ko::).
* `int trymove(int pos, int color, const char *message)'
Returns true if `(pos)' is a legal move for `color'. In that
case, it pushes the board on the stack and makes the move,
incrementing `stackp'. If the reading code is recording
reading variations (as with `--decide-string' or with `-o'),
the string `*message' will be inserted in the SGF file as a
comment. The comment will also refer to the string at `str'
if this is not `0'. The value of `str' can be NO_MOVE if it
is not needed but otherwise the location of `str' is included
* `int tryko(int pos, int color, const char *message)'
`tryko()' pushes the position onto the stack, and makes a move
`pos' of `color'. The move is allowed even if it is an
illegal ko capture. It is to be imagined that `color' has
made an intervening ko threat which was answered and now the
continuation is to be explored. Return 1 if the move is legal
with the above caveat. Returns zero if it is not legal
Pops the move stack. This function must (eventually) be
called after a succesful `trymove' or `tryko' to restore the
board position. It undoes all the changes done by the call to
`trymove/tryko' and leaves the board in the same state as it
*NOTE*: If `trymove/tryko' returns `0', i.e. the tried move
was not legal, you must *not* call `popgo'.
* `int komaster_trymove(int pos, int color, const char *message, int
str, int *is_conditional_ko, int consider_conditional_ko)'
Variation of `trymove'/`tryko' where ko captures (both
conditional and unconditional) must follow a komaster scheme
As you see, `trymove()' plays a move which can be easily retracted
(with `popgo()') and it is call thousands of times per actual game move
as GNU Go analyzes the board position. By contrast the function
`play_move()' plays a move which is intended to be permanent, though it
is still possible to undo it if, for example, the opponent retracts a
* `void play_move(int pos, int color)'
Play a move. If you want to test for legality you should
first call `is_legal()'. This function strictly follows the
1. Place a stone of given color on the board.
2. If there are any adjacent opponent strings without
liberties, remove them and increase the prisoner count.
3. If the newly placed stone is part of a string without
liberties, remove it and increase the prisoner count.
In spite of the name "permanent move", this move can
(usually) be unplayed by `undo_move()', but it is
significantly more costly than unplaying a temporary move.
There are limitations on the available move history, so under
certain circumstances the move may not be possible to unplay
Undo `n' permanent moves. Returns 1 if successful and 0 if it
fails. If `n' moves cannot be undone, no move is undone.
Other board functions are documented in *Note Board Utilities::.
File: gnugo.info, Node: SGF, Next: DFA, Prev: Libboard, Up: Top
16 Handling SGF trees in memory
*******************************
"SGF" - Smart Game Format - is a file format which is used for storing
game records for a number of different games, among them chess and go.
The format is a framework with special adaptions to each game. This is
not a description of the file format standard. Too see the exact
definition of the file format, see `http://www.red-bean.com/sgf/'.
GNU Go contains a library to handle go game records in the SGF
format in memory and to read and write SGF files. This library -
`libsgf.a' - is in the `sgf' subdirectory. To use the SGF routines,
include the file `sgftree.h'.
Each game record is stored as a tree of "nodes", where each node
represents a state of the game, often after some move is made. Each node
contains zero or more "properties", which gives meaning to the node.
There can also be a number of "child nodes" which are different
variations of the game tree. The first child node is the main variation.
Here is the definition of `SGFNode', and `SGFProperty', the data
structures which are used to encode the game tree.
typedef struct SGFProperty_t {
struct SGFProperty_t *next;
typedef struct SGFNode_t {
struct SGFNode_t *parent;
Each node of the SGF tree is stored in an `SGFNode' struct. It has a
pointer to a linked list of properties (see below) called `props'. It
also has a pointer to a linked list of children, where each child is a
variation which starts at this node. The variations are linked through
the `next' pointer and each variation continues through the `child'
pointer. Each and every node also has a pointer to its parent node (the
`parent' field), except the top node whose parent pointer is `NULL'.
An SGF property is encoded in the `SGFPoperty' struct. It is linked
in a list through the `next' field. A property has a `name' which is
encoded in a short int. Symbolic names of properties can be found in
Some properties also have a value, which could be an integer, a
floating point value, a character or a string. These values can be
accessed or set through special functions.
16.1 The SGFTree datatype
=========================
Sometimes we just want to record an ongoing game or something similarly
simple and not do any sofisticated tree manipulation. In that case we
can use the simplified interface provided by `SGFTree' below.
typedef struct SGFTree_t {
An `SGFTree' contains a pointer to the root node of an SGF tree and
a pointer to the node that we last accessed. Most of the time this will
be the last move of an ongoing game.
Most of the functions which manipulate an `SGFTree' work exactly
like their `SGFNode' counterparts, except that they work on the current
All the functions below that take arguments `tree' and `node' will
2. `tree->lastnode' if non-`NULL'
3. The current end of the game tree.
File: gnugo.info, Node: API, Next: GTP, Prev: Utility Functions, Up: Top
17 Application Programmers Interface to GNU Go
**********************************************
If you want to write your own interface to GNU Go, or if you want to
create a go application using the GNU Go engine, this chapter is of
First an overview: GNU Go consists of two parts: the GNU Go engine
and a program (user interface) which uses this engine. These are linked
together into one binary. The current program implements the following
* An interactive board playable on ASCII terminals
* solo play - GNU Go plays against itself
* replay - a mode which lets the user investigate moves in an
* GMP - Go Modem Protocol, a protocol for automatic play between two
* GTP - Go Text Protocol, a more general go protocol, *note GTP::.
The GNU Go engine can be used in other applications. For example,
supplied with GNU Go is another program using the engine, called
`debugboard', in the directory `interface/debugboard/'. The program
debugboard lets the user load SGF files and can then interactively look
at different properties of the position such as group status and eye
The purpose of this Chapter is to show how to interface your own
program such as `debugboard' with the GNU Go engine.
Figure 1 describes the structure of a program using the GNU Go
+-----------------------------------+
+-----+----------+------+ |
| handling | generation | |
+----------+------------+-----------+
+-----------------------------------+
Figure 1: The structure of a program using the GNU Go engine
The foundation is a library called `libboard.a' which provides
efficient handling of a go board with rule checks for moves, with
incremental handling of connected strings of stones and with methods to
efficiently hash go positions.
On top of this, there is a library which helps the application use
Smart Game Format (SGF) files, with complete handling of game trees in
memory and in files. This library is called `libsgf.a'
The main part of the code within GNU Go is the move generation
library which given a position generates a move. This part of the
engine can also be used to manipulate a go position, add or remove
stones, do tactical and strategic reading and to query the engine for
legal moves. These functions are collected into `libengine.a'.
The game handling code helps the application programmer keep tracks
of the moves in a game. Games can be saved to SGF files and then later
be read back again. These are also within `libengine.a'.
The responsibility of the application is to provide the user with a
user interface, graphical or not, and let the user interact with the
* Getting Started:: How to use the engine in your program
* Basic Data Structures:: Basic Data Structures in the Engine
* The Board State:: The board_state `struct'
* Positional Functions:: Functions which manipulate a Position
File: gnugo.info, Node: Getting Started, Next: Basic Data Structures, Up: API
17.1 How to use the engine in your own program: getting started
===============================================================
To use the GNU Go engine in your own program you must include the file
`gnugo.h'. This file describes the whole public API. There is another
file, `liberty.h', which describes the internal interface within the
engine. If you want to make a new module within the engine, e.g. for
suggesting moves you will have to include this file also. In this
section we will only describe the public interface.
Before you do anything else, you have to call the function
`init_gnugo()'. This function initializes everything within the engine.
It takes one parameter: the number of megabytes the engine can use for
the internal hash table. In addition to this the engine will use a few
megabytes for other purposes such as data describing groups (liberties,
life status, etc), eyes and so on.
File: gnugo.info, Node: Basic Data Structures, Next: The Board State, Prev: Getting Started, Up: API
17.2 Basic Data Structures in the Engine
========================================
There are some basic definitions in gnugo.h which are used everywhere.
The most important of these are the numeric declarations of colors.
Each intersection on the board is represented by one of these:
There is a macro, `OTHER_COLOR(color)' which can be used to get the
other color than the parameter. This macro can only be used on `WHITE'
or `BLACK', but not on `EMPTY'.
GNU Go uses two different representations of the board, for most
purposes a one-dimensional one, but for a few purposes a two
dimensional one (*note Libboard::). The one-dimensional board was
introduced before GNU Go 3.2, while the two-dimensional board dates
back to the ancestral program written by Man Lung Li before 1995. The
API still uses the two-dimensional board, so the API functions have not
changed much since GNU Go 3.0.
File: gnugo.info, Node: The Board State, Next: Positional Functions, Prev: Basic Data Structures, Up: API
17.3 The board_state struct
===========================
A basic data structure in the engine is the `board_state' struct. This
structure is internal to the engine and is defined in `liberty.h'.
typedef unsigned char Intersection;
Intersection board[BOARDSIZE];
Intersection initial_board[BOARDSIZE];
int initial_board_ko_pos;
int initial_white_captured;
int initial_black_captured;
int move_history_color[MAX_MOVE_HISTORY];
int move_history_pos[MAX_MOVE_HISTORY];
int move_history_pointer;
Here `Intersection' stores `EMPTY', `WHITE' or `BLACK'. It is
currently defined as an `unsigned char' to make it reasonably efficient
in both storage and access time. The board state contains an array of
`Intersection''s representing the board. The move history is contained
in the struct. Also contained in the struct is the location of a ko
(`EMPTY') if the last move was not a ko capture, the komi, the number
of captures, and corresponding data for the initial position at the
beginning of the move history.
File: gnugo.info, Node: Positional Functions, Prev: The Board State, Up: API
17.4 Functions which manipulate a Position
==========================================
All the functions in the engine that manipulate Positions have names
prefixed by `gnugo_'. These functions still use the two-dimensional
representation of the board (*note The Board Array::). Here is a
complete list, as prototyped in `gnugo.h':
* `void init_gnugo(float memory)'
Initialize the gnugo engine. This needs to be called once
* `void gnugo_clear_board(int boardsize)'
* `void gnugo_set_komi(float new_komi)'
* `void gnugo_add_stone(int i, int j, int color)'
Place a stone on the board
* `void gnugo_remove_stone(int i, int j)'
Remove a stone from the board
* `int gnugo_is_pass(int i, int j)'
Return true if (i,j) is PASS_MOVE
* `void gnugo_play_move(int i, int j, int color)'
Play a move and start the clock
* `int gnugo_undo_move(int n)'
Undo n permanent moves. Returns 1 if successful and 0 if it
fails. If n moves cannot be undone, no move is undone.
* `int gnugo_play_sgfnode(SGFNode *node, int to_move)'
Perform the moves and place the stones from the SGF node on
the board. Return the color of the player whose turn it is to
* `int gnugo_play_sgftree(SGFNode *root, int *until, SGFNode
Play the moves in ROOT UNTIL movenumber is reached. Return
the color of the player whose turn it is to move.
* `int gnugo_is_legal(int i, int j, int color)'
Interface to `is_legal()'.
* `int gnugo_is_suicide(int i, int j, int color)'
Interface to `is_suicide()'.
* `int gnugo_placehand(int handicap)'
Interface to placehand. Sets up handicap pieces and returns
the number of placed handicap stones.
* `void gnugo_recordboard(SGFNode *root)'
Interface to `sgffile_recordboard()'
* `int gnugo_sethand(int handicap, SGFNode *node)'
Interface to placehand. Sets up handicap stones and returns
the number of placed handicap stones, updating the sgf file
* `float gnugo_genmove(int *i, int *j, int color, int *resign)'
Interface to `genmove()'.
* `int gnugo_attack(int m, int n, int *i, int *j)'
* `int gnugo_find_defense(int m, int n, int *i, int *j)'
Interface to `find_defense()'.
* `void gnugo_who_wins(int color, FILE *outfile)'
Interface to `who_wins()'.
* `float gnugo_estimate_score(float *upper, float *lower)'
Put upper and lower score estimates into `*upper', `*lower'
and return the average. A positive score favors white. In
computing the upper bound, `CRITICAL' dragons are awarded to
white; in computing the lower bound, they are awarded to
* `void gnugo_examine_position(int color, int how_much)'
Interface to `examine_position'.
* `void gnugo_get_board(int b[MAX_BOARD][MAX_BOARD])'
Place the board into the `b' array.
* `int gnugo_get_boardsize()'
* `int gnugo_get_move_number()'
The functions (in *note Positional Functions::) are all that are needed
to create a fully functional go program. But to make the life easier
for the programmer, there is a small set of functions specially
designed for handling ongoing games.
The data structure describing an ongoing game is the `Gameinfo'. It
int to_move; /* whose move it currently is */
SGFTree game_record; /* Game record in sgf format. */
int computer_player; /* BLACK, WHITE, or EMPTY (used as BOTH) */
char outfilename[128]; /* Trickle file */
The meaning of `handicap' should be obvious. `to_move' is the color
of the side whose turn it is to move.
The SGF tree `game_record' is used to store all the moves in the
entire game, including a header node which contains, among other
things, komi and handicap.
If one or both of the opponents is the computer, the field
`computer_player' is used. Otherwise it can be ignored.
GNU Go can use a trickle file to continuously save all the moves of
an ongoing game. This file can also contain information about internal
state of the engine such as move reasons for various locations or move
valuations. The name of this file should be stored in `outfilename' and
the file pointer to the open file is stored in `outfile'. If no trickle
file is used, `outfilename[0]' will contain a null character and
`outfile' will be set to `NULL'.
17.5.1 Functions which manipulate a Gameinfo
--------------------------------------------
All the functions in the engine that manipulate Gameinfos have names
prefixed by `gameinfo_'. Here is a complete list, as prototyped in
* `void gameinfo_clear(Gameinfo *ginfo, int boardsize, float komi)'
Initialize the `Gameinfo' structure.
* `void gameinfo_print(Gameinfo *ginfo)'
* `void gameinfo_load_sgfheader(Gameinfo *gameinfo, SGFNode *head)'
Reads header info from sgf structure and sets the appropriate
* `void gameinfo_play_move(Gameinfo *ginfo, int i, int j, int color)'
Make a move in the game. Return 1 if the move was legal. In
that case the move is actually done. Otherwise return 0.
* `int gameinfo_play_sgftree_rot(Gameinfo *gameinfo, SGFNode *head,
const char *untilstr, int orientation)'
Play the moves in an SGF tree. Walk the main variation,
actioning the properties into the playing board. Returns the
color of the next move to be made. Head is an sgf tree.
Untilstr is an optional string of the form either 'L12' or
'120' which tells it to stop playing at that move or move
number. When debugging, this is the location of the move
* `int gameinfo_play_sgftree(Gameinfo *gameinfo, SGFNode *head,
Same as previous function, using standard orientation.
File: gnugo.info, Node: Utility Functions, Next: API, Prev: DFA, Up: Top
In this Chapter, we document some of the utilities which may be called
* General Utilities:: Utilities from `engine/utils.c'
* Print Utilities:: Utilities from `engine/printutils.c'
* Board Utilities:: Utilities from `engine/board.c'
* Influence Utilities:: Utilities from `engine/influence.c'
File: gnugo.info, Node: General Utilities, Next: Print Utilities, Up: Utility Functions
Utility functions from `engine/utils.c'. Many of these functions
underlie autohelper functions (*note Autohelper Functions::).
* `void change_dragon_status(int dr, int status)'
Change the status of all the stones in the dragon at `dr'.
* `int defend_against(int move, int color, int apos)'
Check whether a move at `move' stops the enemy from playing
* `int cut_possible(int pos, int color)'
Returns true if `color' can cut at `pos', or if connection
through `pos' is inhibited. This information is collected by
`find_cuts()', using the B patterns in the connections
* `int does_attack(int move, int str)'
returns true if the move at `move' attacks `str'. This means
that it captures the string, and that `str' is not already
* `int does_defend(int move, int str)'
`does_defend(move, str)' returns true if the move at `move'
defends `str'. This means that it defends the string, and that
`str' can be captured if no defense is made.
* `int somewhere(int color, int last_move, ...)'
Example: `somewhere(WHITE, 2, apos, bpos, cpos)'. Returns
true if one of the vertices listed satisfies
`board[pos]==color'. Here num_moves is the number of moves
minus one. If the check is true the dragon is not allowed to
be dead. This check is only valid if `stackp==0'.
* `int visible_along_edge(int color, int apos, int bpos)'
Search along the edge for the first visible stone. Start at
apos and move in the direction of bpos. Return 1 if the first
visible stone is of the given color. It is required that apos
and bpos are at the same distance from the edge.
* `int test_symmetry_after_move(int move, int color, int strict)'
Is the board symmetric (or rather antisymmetric) with respect
to mirroring in tengen after a specific move has been played?
If the move is PASS_MOVE, check the current board. If strict
is set we require that each stone is matched by a stone of
the opposite color at the mirrored vertex. Otherwise we only
require that each stone is matched by a stone of either color.
* `int play_break_through_n(int color, int num_moves, ...)'
The function `play_break_through_n()' plays a sequence of
moves, alternating between the players and starting with
color. After having played through the sequence, the three
last coordinate pairs gives a position to be analyzed by
`break_through()', to see whether either color has managed to
enclose some stones and/or connected his own stones. If any
of the three last positions is empty, it's assumed that the
enclosure has failed, as well as the attempt to connect. If
one or more of the moves to play turns out to be illegal for
some reason, the rest of the sequence is played anyway, and
`break_through()' is called as if nothing special happened.
Like `break_through()', this function returns 1 if the
attempt to break through was succesful and 2 if it only
* `int play_attack_defend_n(int color, int do_attack, int num_moves,
* `int play_attack_defend2_n(int color, int do_attack, int
The function `play_attack_defend_n()' plays a sequence of
moves, alternating between the players and starting with
`color'. After having played through the sequence, the last
coordinate pair gives a target to attack or defend, depending
on the value of do_attack. If there is no stone present to
attack or defend, it is assumed that it has already been
captured. If one or more of the moves to play turns out to be
illegal for some reason, the rest of the sequence is played
anyway, and attack/defense is tested as if nothing special
happened. Conversely, `play_attack_defend2_n()' plays a
sequence of moves, alternating between the players and
starting with `color'. After having played through the
sequence, the two last coordinate pairs give two targets to
simultaneously attack or defend, depending on the value of
do_attack. If there is no stone present to attack or defend,
it is assumed that it has already been captured. If one or
more of the moves to play turns out to be illegal for some
reason, the rest of the sequence is played anyway, and
attack/defense is tested as if nothing special happened. A
typical use of these functions is to set up a ladder in an
autohelper and see whether it works or not.
* `int play_connect_n(int color, int do_connect, int num_moves, ...)'
Plays a sequence of moves, alternating between the players
and starting with `color'. After having played through the
sequence, the two last coordinates give two targets that
should be connected or disconnected, depending on the value
of do_connect. If there is no stone present to connect or
disconnect, it is assumed that the connection has failed. If
one or more of the moves to play turns out to be illegal for
some reason, the rest of the sequence is played anyway, and
connection/disconnection is tested as if nothing special
happened. Ultimately the connection is decided by the
functions `string_connect' and `disconnect' (*note Connection
* `void set_depth_values(int level)'
It is assumed in reading a ladder if `stackp >= depth' that
as soon as a bounding stone is in atari, the string is safe.
Similar uses are made of the other depth parameters such as
`backfill_depth' and so forth. In short, simplifying
assumptions are made when `stackp' is large. Unfortunately
any such scheme invites the "horizon effect," in which a
stalling move is perceived as a win, by pushing the
refutation past the "horizon"--the value of `stackp' in which
the reading assumptions are relaxed. To avoid the depth it is
sometimes necessary to increase the depth parameters. This
function can be used to set the various reading depth
parameters. If `mandated_depth_value' is not -1 that value is
used; otherwise the depth values are set as a function of
level. The parameter `mandated_depth_value' can be set at the
command line to force a particular value of depth; normally
* `void modify_depth_values(int n)'
Modify the various tactical reading depth parameters. This is
typically used to avoid horizon effects. By temporarily
increasing the depth values when trying some move, one can
avoid that an irrelevant move seems effective just because
the reading hits a depth limit earlier than it did when
reading only on relevant moves.
* `void increase_depth_values(void)'
`modify_depth_values(1)'.
* `void decrease_depth_values(void)'
`modify_depth_values(-1)'.
* `void restore_depth_values()'
Sets `depth' and so forth to their saved values.
* `void set_temporary_depth_values(int d, int b, int b2, int bc, int
ss, int br, int f, int k)'
Explicitly set the depth values. This function is currently
* `int confirm_safety(int move, int color, int *defense_point, char
Check that the move at color doesn't involve any kind of
blunder, regardless of size.
* `float blunder_size(int move, int color, int *defense_point, char
This function will detect some blunders. If the move reduces
the number of liberties of an adjacent friendly string, there
is a danger that the move could backfire, so the function
checks that no friendly worm which was formerly not
attackable becomes attackable, and it checks that no opposing
worm which was not defendable becomes defendable. It returns
the estimated size of the blunder, or 0.0 if nothing bad has
happened. The array `safe_stones[]' contains the stones that
are supposedly safe after `move'. It may be `NULL'. For use
when called from `fill_liberty()', this function may
optionally return a point of defense, which, if taken, will
presumably make the move at `move' safe on a subsequent turn.
* `int double_atari(int move, int color, float *value, char
Returns true if a move by (color) fits the following shape:
capturing one of the two `X' strings. The name is a slight
misnomer since this includes attacks which are not
necessarily double ataris, though the common double atari is
the most important special case. If `safe_stones != NULL',
then only attacks on stones marked as safe are tried. The
value of the double atari attack is returned in value (unless
value is `NULL'), and the attacked stones are marked unsafe.
* `void unconditional_life(int unconditional_territory[BOARDMAX],
Find those worms of the given color that can never be
captured, even if the opponent is allowed an arbitrary number
of consecutive moves. The coordinates of the origins of these
worms are written to the worm arrays and the number of
non-capturable worms is returned. The algorithm is to cycle
through the worms until none remains or no more can be
captured. A worm is removed when it is found to be
capturable, by letting the opponent try to play on all its
liberties. If the attack fails, the moves are undone. When no
more worm can be removed in this way, the remaining ones are
unconditionally alive. After this, unconditionally dead
opponent worms and unconditional territory are identified. To
find these, we continue from the position obtained at the end
of the previous operation (only unconditionally alive strings
remain for color) with the following steps:
1. Play opponent stones on all liberties of the
unconditionally alive strings except where illegal.
(That the move order may determine exactly which
liberties can be played legally is not important. Just
pick an arbitrary order).
2. Recursively extend opponent strings in atari, except
where this would be suicide.
3. Play an opponent stone anywhere it can get two empty
neighbors. (I.e. split big eyes into small ones).
4. an opponent stone anywhere it can get one empty
neighbor. (I.e. reduce two space eyes to one space eyes.)
Remaining opponent strings in atari and remaining
liberties of the unconditionally alive strings
constitute the unconditional territory. Opponent
strings from the initial position placed on
unconditional territory are unconditionally dead. On
return, `unconditional_territory[][]' is 1 where color
has unconditionally alive stones, 2 where it has
unconditional territory, and 0 otherwise.
* `void who_wins(int color, FILE *outfile)'
Score the game and determine the winner
* `void find_superstring(int str, int *num_stones, int *stones)'
Find the stones of an extended string, where the extensions
are through the following kinds of connections:
1. Solid connections (just like ordinary string).
2. Diagonal connection or one space jump through an
intersection where an opponent move would be suicide or
4. Diagonal connection where both adjacent intersections
5. Connection through adjacent or diagonal tactically
captured stones. Connections of this type are omitted
when the superstring code is called from reading.c, but
included when the superstring code is called from owl.c
* `void find_superstring_liberties(int str, int *num_libs, int
This function computes the superstring at `str' as described
above, but omitting connections of type 5. Then it constructs
a list of liberties of the superstring which are not already
liberties of `str'. If `liberty_cap' is nonzero, only
liberties of substrings of the superstring which have fewer
than `liberty_cap' liberties are generated.
* `void find_proper_superstring_liberties(int str, int *num_libs,
int *libs, int liberty_cap)'
This function is the same as find_superstring_liberties, but
it omits those liberties of the string `str', presumably
since those have already been treated elsewhere. If
`liberty_cap' is nonzero, only liberties of substrings of the
superstring which have at most `liberty_cap' liberties are
* `void find_superstring_stones_and_liberties(int str, int
*num_stones, int *stones, int *num_libs, int *libs, int
This function computes the superstring at `str' as described
above, but omitting connections of type 5. Then it constructs
a list of liberties of the superstring which are not already
liberties of `str'. If liberty_cap is nonzero, only liberties
of substrings of the superstring which have fewer than
liberty_cap liberties are generated.
* `void superstring_chainlinks(int str, int *num_adj, int
adjs[MAXCHAIN], int liberty_cap)'
analogous to chainlinks, this function finds boundary chains
of the superstring at `str', including those which are
boundary chains of `str' itself. If `liberty_cap != 0', only
those boundary chains with `<= liberty_cap' liberties are
* `void proper_superstring_chainlinks(int str, int *num_adj, int
adjs[MAXCHAIN], int liberty_cap)'
analogous to chainlinks, this function finds boundary chains
of the superstring at `str', omitting those which are
boundary chains of `str' itself. If `liberty_cap != 0', only
those boundary chains with `<= liberty_cap' liberties are
* `void start_timer(int n)'
Start a timer. GNU Go has four internal timers available for
assessing the time spent on various tasks.
* `double time_report(int n, const char *occupation, int move,
Report time spent and restart the timer. Make no report if
elapsed time is less than mintime.
File: gnugo.info, Node: Print Utilities, Next: Board Utilities, Prev: General Utilities, Up: Utility Functions
Functions in `engine/printutils.c' do formatted printing similar to
`printf' and its allies. The following formats are recognized:
* `%c', `%d', `%f', `%s', `%x'
These have their usual meaning in formatted output, printing
a character, integer, float, string or hexadecimal,
`Outdent.' Normally output is indented by `2*stackp' spaces,
so that the depth can be seen at a glance in traces. At the
beginning of a format, this `%o' inhibits the indentation.
Print a color as a string.
Takes 2 integers and writes a move, using the two dimensional
board representation (*note The Board Array::)
Takes 1 integers and writes a move, using the one dimensional
board representation (*note The Board Array::)
We list the non statically declared functions in `printutils.c'.
* `void gfprintf(FILE *outfile, const char *fmt, ...)'
Formatted output to `outfile'.
* `int gprintf(const char *fmt, ...)'
Formatted output to stderr. Always returns 1 to allow use in
short-circuit logical expressions.
* `int mprintf(const char *fmt, ...)'
Formatted output to stdout.
* `DEBUG(level, fmt, args...)'
If `level & debug', do formatted output to stderr. Otherwise,
* `void abortgo(const char *file, int line, const char *msg, int
Print debugging output in an error situation, then exit.
* `const char * color_to_string(int color)'
Convert a color value to a string
* `const char * location_to_string(int pos)'
Convert a location to a string
* `void location_to_buffer(int pos, char *buf)'
Convert a location to a string, writing to a buffer.
* `int string_to_location(int boardsize, char *str, int *m, int *n)'
Get the `(m, n)' coordinates in the standard GNU Go
coordinate system from the string `str'. This means that `m'
is the nth row from the top and `n' is the column. Both
coordinates are between 0 and `boardsize-1', inclusive.
Return 1 if ok, otherwise return 0;
* `int is_hoshi_point(int m, int n)' True if the coordinate is a
* `void draw_letter_coordinates(FILE *outfile)' Print a line with
coordinate letters above the board.
* `void simple_showboard(FILE *outfile)'
Bare bones version of `showboard(0)'. No fancy options, no
hint of color, and you can choose where to write it.
The following functions are in `showbord.c'. Not all public
functions in that file are listed here.
* `void showboard(int xo)'
xo=0: black and white XO board for ascii game
xo=1: colored dragon display
xo=2: colored eye display
xo=3: colored owl display
xo=4: colored matcher status display
* `const char * status_to_string(int status)'
Convert a status value to a string.
* `const char * safety_to_string(int status)'
Convert a safety value to a string.
* `const char * result_to_string(int result)'
Convert a read result to a string
File: gnugo.info, Node: Board Utilities, Next: Influence Utilities, Prev: Print Utilities, Up: Utility Functions
The functions documented in this section are from `board.c'. Other
functions in `board.c' are described in *Note Some Board Functions::.
* `void store_board(struct board_state *state)'
* `void restore_board(struct board_state *state)'
Restore a saved board state.
* `void clear_board(void)'
Clear the internal board.
* `void dump_stack(void)'
for use under GDB prints the move stack.
* `void add_stone(int pos, int color)'
Place a stone on the board and update the board_hash. This
operation destroys all move history.
* `void remove_stone(int pos)'
Remove a stone from the board and update the board_hash. This
operation destroys the move history.
Test if the move is a pass or not. Return 1 if it is.
* `int is_legal(int pos, int color)'
Determines whether the move `color' at `pos' is legal.
* `int is_suicide(int pos, int color)'
Determines whether the move `color' at `pos' would be a
suicide. This is the case if
1. There is no neighboring empty intersection.
2. There is no neighboring opponent string with exactly one
3. There is no neighboring friendly string with more than
* `int is_illegal_ko_capture(int pos, int color)'
Determines whether the move `color' at `pos' would be an
* `int is_edge_vertex(int pos)'
Determine whether vertex is on the edge.
* `int edge_distance(int pos)'
* `int is_corner_vertex(int pos)'
Determine whether vertex is a corner.
Public functions to access the variable `komaster' and
`kom_pos', which are static in `board.c'.
Next we come to `countlib()' and its allies, which address the
problem of determining how many liberties a string has. Although
`countlib()' addresses this basic question, other functions can often
get the needed information more quickly, so there are a number of
different functions in this family.
* `int countlib(int str)'
Count the number of liberties of the string at `pos'. There
must be a stone at this location.
* `int findlib(int str, int maxlib, int *libs)'
Find the liberties of the string at `str'. This location must
not be empty. The locations of up to maxlib liberties are
written into `libs[]'. The full number of liberties is
returned. If you want the locations of all liberties,
whatever their number, you should pass `MAXLIBS' as the value
for `maxlib' and allocate space for `libs[]' accordingly.
* `int fastlib(int pos, int color, int ignore_captures)'
Count the liberties a stone of the given color would get if
played at `pos'. The intent of this function is to be as fast
as possible, not necessarily complete. But if it returns a
positive value (meaning it has succeeded), the value is
guaranteed to be correct. Captures are ignored based if the
`ignore_captures' field is nonzero. The location `pos' must
be empty. The function fails if there are more than two
neighbor strings of the same color. In this case, the return
value is -1. Captures are handled in a very limited way, so
if ignore_capture is 0, and a capture is required, it will
* `int approxlib(int pos, int color, int maxlib, int *libs)'
Find the liberties a stone of the given color would get if
played at `pos', ignoring possible captures of opponent
stones. The location `pos' must be empty. If `libs != NULL',
the locations of up to `maxlib' liberties are written into
`libs[]'. The counting of liberties may or may not be halted
when `maxlib' is reached. The number of liberties found is
returned, which may be less than the total number of
liberties if `maxlib' is small. If you want the number or the
locations of all liberties, however many they are, you should
pass `MAXLIBS' as the value for maxlib and allocate space for
* `int accuratelib(int pos, int color, int maxlib, int *libs)'
Find the liberties a stone of the given color would get if
played at `pos'. This function takes into consideration all
captures. Its return value is exact in that sense it counts
all the liberties, unless `maxlib' allows it to stop earlier.
The location `pos' must be empty. If `libs != NULL', the
locations of up to `maxlib' liberties are written into
`libs[]'. The counting of liberties may or may not be halted
when `maxlib' is reached. The number of found liberties is
returned. This function guarantees that liberties which are
not results of captures come first in `libs[]' array. To find
whether all the liberties starting from a given one are
results of captures, one may use `if (board[libs[k]] !=
EMPTY)' construction. If you want the number or the
locations of all liberties, however many they are, you should
pass `MAXLIBS' as the value for `maxlib' and allocate space
for `libs[]' accordingly.
Next we have some general utility functions.
* `int count_common_libs(int str1, int str2)'
Find the number of common liberties of the two strings.
* `int find_common_libs(int str1, int str2, int maxlib, int *libs)'
Find the common liberties of the two strings. The locations
of up to `maxlib' common liberties are written into `libs[]'.
The full number of common liberties is returned. If you want
the locations of all common liberties, whatever their number,
you should pass `MAXLIBS' as the value for `maxlib' and
allocate space for `libs[]' accordingly.
* `int have_common_lib(int str1, int str2, int *lib)'
Determine whether two strings have at least one common
liberty. If they do and `lib != NULL', one common liberty is
* `int countstones(int str)'
Report the number of stones in a string.
* `int findstones(int str, int maxstones, int *stones)'
Find the stones of the string at `str'. The location must not
be empty. The locations of up to maxstones stones are written
into `stones[]'. The full number of stones is returned.
* `int chainlinks(int str, int adj[MAXCHAIN])'
This very useful function returns (in the `adj' array) the
chains surrounding the string at `str'. The number of chains
* `int chainlinks2(int str, int adj[MAXCHAIN], int lib)'
Returns (in `adj' array) those chains surrounding the string
at `str', which has exactly `lib' liberties. The number of
* `int chainlinks3(int str, int adj[MAXCHAIN], int lib)'
Returns (in `adj' array) the chains surrounding the string at
`str', which have less or equal `lib' liberties. The number
of such chains is returned.
* `int extended_chainlinks(int str, int adj[MAXCHAIN], int
Returns (in the `adj' array) the opponent strings being
directly adjacent to `str' or having a common liberty with
`str'. The number of such strings is returned. If the
both_colors parameter is true, also own strings sharing a
* `int find_origin(int str)'
Find the origin of a string, i.e. the point with the smallest
1D board coordinate. The idea is to have a canonical
reference point for a string.
* `int is_self_atari(int pos, int color)'
Determine whether a move by color at `pos' would be a self
atari, i.e. whether it would get more than one liberty. This
function returns true also for the case of a suicide move.
* `int liberty_of_string(int pos, int str)'
Returns true if `pos' is a liberty of the string at `str'.
* `int second_order_liberty_of_string(int pos, int str)'
Returns true if `pos' is a second order liberty of the string
* `int neighbor_of_string(int pos, int str)'
Returns true if `pos' is adjacent to the string at `str'.
* `int has_neighbor(int pos, int color)'
Returns true if `pos' has a neighbor of `color'.
* `int same_string(int str1, int str2)'
Returns true if `str1' and `str2' belong to the same string.
* `int adjacent_strings(int str1, int str2)'
Returns true if the strings at `str1' and `str2' are adjacent.
* `int is_ko(int pos, int color, int *ko_pos)'
Return true if the move `pos' by `color' is a ko capture
(whether capture is legal on this move or not). If so, and if
`ko_pos' is not a `NULL' pointer, then `*ko_pos' returns the
location of the captured ko stone. If the move is not a ko
capture, `*ko_pos' is set to 0. A move is a ko capture if
1. All neighbors are opponent stones.
2. The number of captured stones is exactly one.
* `int is_ko_point(int pos)'
Return true if `pos' is either a stone, which if captured
would give ko, or if `pos' is an empty intersection adjacent
* `int does_capture_something(int pos, int color)'
Returns 1 if at least one string is captured when color plays
* `void mark_string(int str, char mx[BOARDMAX], char mark)'
For each stone in the string at pos, set `mx' to value mark.
If some of the stones in the string are marked prior to
calling this function, only the connected unmarked stones
starting from pos are guaranteed to become marked. The rest
of the string may or may not become marked. (In the current
implementation, it will.)
* `int move_in_stack(int pos, int cutoff)'
Returns true if at least one move has been played at pos at
deeper than level `cutoff' in the reading tree.
* `int stones_on_board(int color)'
Return the number of stones of the indicated color(s) on the
board. This only counts stones in the permanent position,
not stones placed by `trymove()' or `tryko()'. Use
`stones_on_board(BLACK | WHITE)' to get the total number of
File: gnugo.info, Node: Influence Utilities, Prev: Board Utilities, Up: Utility Functions
18.4 Utilities from `engine/influence.c'
========================================
We will only list here a portion of the public functions in
`influence.c'. The influence code is invoked through the function
`compute_influence' (*note Influence Usage::). It is invoked as follows.
* `void compute_influence(int color, const char
safe_stones[BOARDMAX], const float strength[BOARDMAX], struct
influence_data *q, int move, const char *trace_message)'
Compute the influence values for both colors. The caller must
- set up the `board[]' state
- mark safe stones with `INFLUENCE_SAFE_STONE', dead
- mark stones newly saved by a move with
`INFLUENCE_SAVED_STONE' (this is relevant if the
influence_data *q is reused to compute a followup value
Results will be stored in q. `move' has no effects except
toggling debugging. Set it to -1 for no debug output at all
(otherwise it will be controlled by the `-m' command line
option). It is assumed that `color' is in turn to move. (This
affects the barrier patterns (class A, D) and intrusions
Other functions in `influence.c' are of the nature of utilities
which may be useful throughout the engine. We list the most useful ones
* `void influence_mark_non_territory(int pos, int color)'
Called from actions for `t' patterns in `barriers.db'. Marks
`pos' as not being territory for `color'.
* `int whose_territory(const struct influence_data *q, int pos)'
Return the color of the territory at `pos'. If it's territory
for neither color, `EMPTY' is returned.
* `int whose_moyo(const struct influence_data *q, int pos)'
Return the color who has a moyo at `pos'. If neither color
has a moyo there, `EMPTY' is returned. The definition of moyo
in terms of the influences is totally ad hoc.
* `int whose_area(const struct influence_data *q, int pos)'
Return the color who has dominating influence ("area") at
`pos'. If neither color dominates the influence there, EMPTY
is returned. The definition of area in terms of the
influences is totally ad hoc.
File: gnugo.info, Node: GTP, Next: Regression, Prev: API, Up: Top
* The Go Text Protocol:: The Go Text Protocol
* Running in GTP mode:: Running GNU Go in GTP mode
* GTP applications:: GTP applications
* The Metamachine:: The Metamachine
* Adding new GTP commands:: Adding new GTP commands
* GTP command reference:: Details on every GTP command
File: gnugo.info, Node: The Go Text Protocol, Next: Running in GTP mode, Up: GTP
19.1 The Go Text Protocol
=========================
GNU Go 3.0 introduced a new interface, the Go Text Protocol, abbreviated
GTP. The intention was to make an interface that is better suited for
machine-machine communication than the ascii interface and simpler, more
powerful, and more flexible than the Go Modem Protocol.
There are two versions of the protocol. Version 1 was used with GNU
Go 3.0 and 3.2. GNU Go 3.4 and later versions use protocol version 2.
The specification of GTP version 2 is available at
`http://www.lysator.liu.se/~gunnar/gtp/'. GNU Go 3.4 is the reference
implementation for GTP version 2, but all but the most common commands
are to be regarded as private extensions of the protocol.
The GTP has a variety of applications. For GNU Go the first use was
in regression testing (*note Regression::), followed by communication
with the NNGS go server and for automated test games against itself and
other programs. Now there are also many graphical user interfaces
available supporting GTP, as well as bridges to other Go servers than
File: gnugo.info, Node: Running in GTP mode, Next: GTP applications, Prev: The Go Text Protocol, Up: GTP
19.2 Running GNU Go in GTP mode
===============================
To start GNU Go in GTP mode, simply invoke it with the option `--mode
gtp'. You will not get a prompt or any other output to start with but
GNU Go is silently waiting for GTP commands.
A sample GTP session may look as follows:
virihaure 462% ./gnugo --mode gtp
2 . . . . . . . 2 WHITE (O) has captured 0 stones
1 . . . . . . . 1 BLACK (X) has captured 0 stones
Commands are given on a single line, starting by an optional identity
number, followed by the command name and its arguments.
If the command is successful, the response starts by an equals sign
(`='), followed by the identity number of the command (if any) and then
the result. In this example all results were empty strings except for
command 4 where the answer was the white move at C3, and command 7
where the result was a diagram of the current board position. The
response ends by two consecutive newlines.
Failing commands are signified by a question mark (`?') instead of
an equals sign, as in the response to command 5.
The detailed specification of the protocol can be found at
`http://www.lysator.liu.se/~gunnar/gtp/'. The available commands in GNU
Go may always be listed using the command `list_commands'. They are
also documented in *Note GTP command reference::.
File: gnugo.info, Node: GTP applications, Next: The Metamachine, Prev: Running in GTP mode, Up: GTP
GTP is an asymmetric protocol involving two parties which we call
controller and engine. The controller sends all commands and the engine
only responds to these commands. GNU Go implements the engine end of the
With the source code of GNU Go is also distributed a number of
applications implementing the controller end. Among the most
interesting of these are:
* `regression/regress.awk'
Script to run regressions. The script sends GTP commands to
set up and evaluate positions to the engine and then analyzes
the responses from the engine. More information about GTP
based regression testing can be found in the regression
chapter (*note Regression::).
* `regression/regress.pl'
Perl script to run regressions, giving output which together
with the CGI script `regression/regress.plx' generates HTML
views of the regressions.
* `regression/regress.pike'
Pike script to run regressions. More feature-rich and
powerful than `regress.awk'.
Pike script to examine a single regression testcase through a
graphical board. This gives an easy way to inspect many of
* `interface/gtp_examples/twogtp'
Perl script to play two engines against each other. The script
essentially sets up both engines with desired boardsize,
handicap, and komi, then relays moves back and forth between
* `interface/gtp_examples/twogtp-a'
An alternative Perl implementation of twogtp.
* `interface/gtp_examples/twogtp.py'
Implementation of twogtp in Python. Has more features than
* `interface/gtp_examples/twogtp.pike'
Implementation of twogtp in Pike. Has even more features than
* `interface/gtp_examples/2ptkgo.pl'
Variation of twogtp which includes a graphical board.
More GTP applications, including bridges to go servers and graphical
user interfaces, are listed at `http://www.lysator.liu.se/~gunnar/gtp/'.
File: gnugo.info, Node: The Metamachine, Next: Adding new GTP commands, Prev: GTP applications, Up: GTP
An interesting application of the GTP is the concept of using GNU Go as
an "Oracle" that can be consulted by another process. This could be
another computer program that asks GNU Go to generate future board
positions, then evaluate them.
David Doshay at the University of California at Santa Cruz has done
interesting experiments with a parallel engine, known as SlugGo, that
is based on GNU Go. These are described in
`http://lists.gnu.org/archive/html/gnugo-devel/2004-08/msg00060.html'.
The "Metamachine" experiment is a more modest approach using the GTP
to communicate with a GNU Go process that is used as an oracle. The
following scheme is used.
* The GNU Go "oracle" is asked to generate its top moves using the
GTP `top_moves' commands.
* Both moves are tried and `estimate_score' is called from the
resulting board position.
* The higher scoring position is selected as the engine's move.
This scheme does not produce a stronger engine, but it is
suggestive, and the SlugGo experiment seems to show that a more
elaborate scheme along the same lines could produce a stronger engine.
Two implementations are distributed with GNU Go. Both make use of
`fork' and `pipe' system calls, so they require a Unix-like
environment. The Metamachine has been tested under GNU/Linux.
*Important:* If the Metamachine terminates normally, the GNU Go
process will be killed. However there is a danger that something will
go wrong. When you are finished running the Metamachine, it is a good
idea to run `ps -A|grep gnugo' or `ps -aux|grep gnugo' to make sure
there are no unterminated processes. (If there are, just kill them.)
19.4.1 The Standalone Metamachine
---------------------------------
In `interface/gtp_examples/metamachine.c' is a standalone
implementation of the Metamachine. Compile it with `cc -o metamachine
metamachine.c' and run it. It forks a `gnugo' process with which it
communicates through the GTP, to use as an oracle.
The following scheme is followed:
GTP client ----> Metamachine -----> GNU Go
Most commands issued by the client are passed along verbatim to GNU
Go by the Metamachine. The exception is gg_genmove, which is
intercepted then processed differently, as described above. The client
is unaware of this, and only knows that it issued a gg_genmove command
and received a reply. Thus to the the Metamachine appears as an
Usage: no arguments gives normal GTP behavior. `metamachine
--debug' sends diagnostics to stderr.
19.4.2 GNU Go as a Metamachine
------------------------------
Alternatively, you may compile GNU Go with the configure option
`--enable-metamachine'. This causes the file `oracle.c' to be compiled,
which contains the Metamachine code. This has no effect on the engine
unless you run GNU Go with the runtime option `--metamachine'. Thus you
must use both the configure and the runtime option to get the
This method is better than the standalone program since you have
access to GNU Go's facilities. For example, you can run the Metamachine
with CGoban or in Ascii mode this way.
You can get traces by adding the command line `-d0x1000000'. In
debugging the Metamachine, a danger is that any small oversight in
designing the program can cause the forked process and the controller
to hang, each one waiting for a response from the other. If this seems
to happen it is useful to know that you can attach `gdb' to a running
process and find out what it is doing.
File: gnugo.info, Node: Adding new GTP commands, Next: GTP command reference, Prev: The Metamachine, Up: GTP
19.5 Adding new GTP commands
============================
The implementation of GTP in GNU Go is distributed over three files,
`interface/gtp.h', `interface/gtp.c', and `interface/play_gtp.c'. The
first two implement a small library of helper functions which can be
used also by other programs. In the interest of promoting the GTP they
are licensed with minimal restrictions (*note GTP License::). The
actual GTP commands are implemented in `play_gtp.c', which has
knowledge about the engine internals.
To see how a simple but fairly typical command is implemented we
look at `gtp_countlib()' (a GNU Go private extension command):
if (!gtp_decode_coord(s, &i, &j))
return gtp_failure("invalid coordinate");
if (BOARD(i, j) == EMPTY)
return gtp_failure("vertex must not be empty");
return gtp_success("%d", countlib(POS(i, j)));
The arguments to the command are passed in the string `s'. In this
case we expect a vertex as argument and thus try to read it with
`gtp_decode_coord()' from `gtp.c'.
A correctly formatted response should start with either `=' or `?',
followed by the identity number (if one was sent), the actual result,
and finally two consecutive newlines. It is important to get this
formatting correct since the controller in the other end relies on it.
Naturally the result itself cannot contain two consecutive newlines but
it may be split over several lines by single newlines.
The easiest way to generate a correctly formatted response is with
one of the functions `gtp_failure()' and `gtp_success()', assuming that
their formatted output does not end with a newline.
Sometimes the output is too complex for use with gtp_success, e.g. if
we want to print vertices, which gtp_success() does not support. Then
we have to fall back to the construction in e.g. `gtp_genmove()':
gtp_start_response(GTP_SUCCESS);
return gtp_finish_response();
Here `gtp_start_response()' writes the equal sign and the identity
number while `gtp_finish_response()' adds the final two newlines. The
next example is from `gtp_list_commands()':
gtp_list_commands(char *s)
gtp_start_response(GTP_SUCCESS);
for (k = 0; commands[k].name != NULL; k++)
gtp_printf("%s\n", commands[k].name);
As we have said, the response should be finished with two newlines.
Here we have to finish up the response ourselves since we already have
one newline in place from the last command printed in the loop.
In order to add a new GTP command to GNU Go, the following pieces of
code need to be inserted in `play_gtp.c':
1. A function declaration using the `DECLARE' macro in the list
2. An entry in the `commands[]' array starting at line 200.
3. An implementation of the function handling the command.
Useful helper functions in `gtp.c'/`gtp.h' are:
* `gtp_printf()' for basic formatted printing.
* `gtp_mprintf()' for printing with special format codes for
* `gtp_success()' and `gtp_failure()' for simple responses.
* `gtp_start_response()' and `gtp_end_response()' for more complex
* `gtp_print_vertex()' and `gtp_print_vertices()' for printing one
* `gtp_decode_color()' to read in a color from the command arguments.
* `gtp_decode_coord()' to read in a vertex from the command
* `gtp_decode_move()' to read in a move, i.e. color plus vertex,
from the command arguments.
File: gnugo.info, Node: GTP command reference, Prev: Adding new GTP commands, Up: GTP
19.6 GTP command reference
==========================
This section lists the GTP commands implemented in GNU Go along with
some information about each command. Each entry in the list has the
* Function: What this command does.
* Arguments: What other information, if any, this command requires.
Typical values include "none" or "vertex" or "integer" (there are
* Fails: Circumstances which cause this command to fail.
* Returns: What is displayed after the "=" and before the two
newlines. Typical values include "nothing" or "a move coordinate"
or some status string (there are others).
* Status: How this command relates to the standard GTP version 2
commands. If nothing else is specified it is a GNU Go private
Without further ado, here is the big list (in no particular order).
Note: if new commands are added by editing `interface/play_gtp.c'
this list could become incomplete. You may rebuild this list in
`doc/gtp-commands.texi' with the command `make gtp-commands' in the
`doc/' directory. This may require GNU sed.
Status: GTP version 2 standard command.
* protocol_version: Report protocol version.
Returns: protocol version number
Status: GTP version 2 standard command.
* name: Report the name of the program.
Status: GTP version 2 standard command.
* version: Report the version number of the program.
Status: GTP version 2 standard command.
* boardsize: Set the board size to NxN and clear the board.
Fails: board size outside engine's limits
Status: GTP version 2 standard command.
* query_boardsize: Find the current boardsize
* clear_board: Clear the board.
Status: GTP version 2 standard command.
* orientation: Set the orienation to N and clear the board
Fails: illegal orientation
* query_orientation: Find the current orientation
Fails: incorrect argument
Status: GTP version 2 standard command.
* black: Play a black stone at the given vertex.
Fails: invalid vertex, illegal move
Status: Obsolete GTP version 1 command.
* playwhite: Play a white stone at the given vertex.
Fails: invalid vertex, illegal move
Status: Obsolete GTP version 1 command.
* play: Play a stone of the given color at the given vertex.
Fails: invalid vertex, illegal move
Status: GTP version 2 standard command.
* fixed_handicap: Set up fixed placement handicap stones.
Arguments: number of handicap stones
Fails: invalid number of stones for the current boardsize
Returns: list of vertices with handicap stones
Status: GTP version 2 standard command.
* place_free_handicap: Choose free placement handicap stones and put
Arguments: number of handicap stones
Fails: invalid number of stones
Returns: list of vertices with handicap stones
Status: GTP version 2 standard command.
* set_free_handicap: Put free placement handicap stones on the board.
Arguments: list of vertices with handicap stones
Fails: board not empty, bad list of vertices
Status: GTP version 2 standard command.
* get_handicap: Get the handicap
* loadsgf: Load an sgf file, possibly up to a move number or the
first occurence of a move.
Arguments: filename + move number, vertex, or nothing
Fails: missing filename or failure to open or parse file
Status: GTP version 2 standard command.
* color: Return the color at a vertex.
Returns: "black", "white", or "empty"
* list_stones: List vertices with either black or white stones.
Returns: list of vertices
* countlib: Count number of liberties for the string at a vertex.
Fails: invalid vertex, empty vertex
Returns: Number of liberties.
* findlib: Return the positions of the liberties for the string at a
Fails: invalid vertex, empty vertex
Returns: Sorted space separated list of vertices.
* accuratelib: Determine which liberties a stone of given color will
get if played at given vertex.
Arguments: move (color + vertex)
Fails: invalid color, invalid vertex, occupied vertex
Returns: Sorted space separated list of liberties
* accurate_approxlib: Determine which liberties a stone of given
color will get if played at given vertex.
Arguments: move (color + vertex)
Fails: invalid color, invalid vertex, occupied vertex
Returns: Sorted space separated list of liberties
Supposedly identical in behavior to the above function and
can be retired when this is confirmed.
* is_legal: Tell whether a move is legal.
Returns: 1 if the move is legal, 0 if it is not.
* all_legal: List all legal moves for either color.
Returns: Sorted space separated list of vertices.
* captures: List the number of captures taken by either color.
Returns: Number of captures.
* last_move: Return the last move.
Fails: no previous move known
Returns: Color and vertex of last move.
* move_history: Print the move history in reverse order
Returns: List of moves played in reverse order in format:
color move (one move per line)
* invariant_hash: Return the rotation/reflection invariant board
Returns: Invariant hash for the board as a hexadecimal number.
* invariant_hash_for_moves: Return the rotation/reflection invariant
board hash obtained by playing all the possible moves for the
Returns: List of moves + invariant hash as a hexadecimal number,
one pair of move + hash per line.
* trymove: Play a stone of the given color at the given vertex.
Arguments: move (color + vertex)
Fails: invalid color, invalid vertex, illegal move
* tryko: Play a stone of the given color at the given vertex,
allowing illegal ko capture.
Arguments: move (color + vertex)
Fails: invalid color, invalid vertex, illegal move
* popgo: Undo a trymove or tryko.
* clear_cache: clear the caches.
* attack: Try to attack a string.
Fails: invalid vertex, empty vertex
Returns: attack code followed by attack point if attack code nonzero.
* attack_either: Try to attack either of two strings
Fails: invalid vertex, empty vertex
Returns: attack code against the strings. Guarantees there
exists a move which will attack one of the two
with attack_code, but does not return the move.
* defend: Try to defend a string.
Fails: invalid vertex, empty vertex
Returns: defense code followed by defense point if defense code nonzero.
* does_attack: Examine whether a specific move attacks a string
Arguments: vertex (move), vertex (dragon)
Fails: invalid vertex, empty vertex
* does_defend: Examine whether a specific move defends a string
Arguments: vertex (move), vertex (dragon)
Fails: invalid vertex, empty vertex
* ladder_attack: Try to attack a string strictly in a ladder.
Fails: invalid vertex, empty vertex
Returns: attack code followed by attack point if attack code nonzero.
* increase_depths: Increase depth values by one.
* decrease_depths: Decrease depth values by one.
* owl_attack: Try to attack a dragon.
Fails: invalid vertex, empty vertex
Returns: attack code followed by attack point if attack code nonzero.
* owl_defend: Try to defend a dragon.
Fails: invalid vertex, empty vertex
Returns: defense code followed by defense point if defense code nonzero.
* owl_threaten_attack: Try to attack a dragon in 2 moves.
Fails: invalid vertex, empty vertex
Returns: attack code followed by the two attack points if
* owl_threaten_defense: Try to defend a dragon with 2 moves.
Fails: invalid vertex, empty vertex
Returns: defense code followed by the 2 defense points if
* owl_does_attack: Examine whether a specific move attacks a dragon.
Arguments: vertex (move), vertex (dragon)
Fails: invalid vertex, empty vertex
* owl_does_defend: Examine whether a specific move defends a dragon.
Arguments: vertex (move), vertex (dragon)
Fails: invalid vertex, empty vertex
* owl_connection_defends: Examine whether a connection defends
Arguments: vertex (move), vertex (dragon1), vertex (dragon2)
Fails: invalid vertex, empty vertex
* defend_both: Try to defend both of two strings
Fails: invalid vertex, empty vertex
Returns: defend code for the strings. Guarantees there
exists a move which will defend both of the two
with defend_code, but does not return the move.
* owl_substantial: Determine whether capturing a string gives a
Fails: invalid vertex, empty vertex
Returns: 1 if dragon can live, 0 otherwise
* analyze_semeai: Analyze a semeai
Arguments: dragona, dragonb
Fails: invalid vertices, empty vertices
Returns: semeai defense result, semeai attack result, semeai move
* analyze_semeai_after_move: Analyze a semeai after a move have been
Arguments: color, vertex, dragona, dragonb
Returns: semeai defense result, semeai attack result, semeai move
* tactical_analyze_semeai: Analyze a semeai, not using owl
Arguments: dragona, dragonb
Fails: invalid vertices, empty vertices
Returns: status of dragona, dragonb assuming dragona moves first
* connect: Try to connect two strings.
Arguments: vertex, vertex
Fails: invalid vertex, empty vertex, vertices of different colors
Returns: connect result followed by connect point if successful.
* disconnect: Try to disconnect two strings.
Arguments: vertex, vertex
Fails: invalid vertex, empty vertex, vertices of different colors
Returns: disconnect result followed by disconnect point if successful.
* break_in: Try to break from string into area.
Arguments: vertex, vertices
Fails: invalid vertex, empty vertex.
Returns: result followed by break in point if successful.
* block_off: Try to block string from area.
Arguments: vertex, vertices
Fails: invalid vertex, empty vertex.
Returns: result followed by block point if successful.
* eval_eye: Evaluate an eye space
Returns: Minimum and maximum number of eyes. If these differ an
attack and a defense point are additionally returned.
If the vertex is not an eye space or not of unique color,
* dragon_status: Determine status of a dragon.
Arguments: optional vertex
Fails: invalid vertex, empty vertex
Returns: status ("alive", "critical", "dead", or "unknown"),
attack point, defense point. Points of attack and
defense are only given if the status is critical.
If no vertex is given, the status is listed for all
dragons, one per row in the format "A4: alive".
FIXME: Should be able to distinguish between life in seki
and independent life. Should also be able to identify ko.
* same_dragon: Determine whether two stones belong to the same
Arguments: vertex, vertex
Fails: invalid vertex, empty vertex
Returns: 1 if the vertices belong to the same dragon, 0 otherwise
* unconditional_status: Determine the unconditional status of a
Returns: unconditional status ("undecided", "alive", "dead",
"white_territory", "black_territory"). Occupied vertices can
be undecided, alive, or dead. Empty vertices can be
undecided, white territory, or black territory.
* combination_attack: Find a move by color capturing something
through a combination attack.
Returns: Recommended move, PASS if no move found
* combination_defend: If color can capture something through a
combination attack, list moves by the opponent of color
to defend against this attack.
Returns: Recommended moves, PASS if no combination attack found.
* aa_confirm_safety: Run atari_atari_confirm_safety().
Arguments: move, optional int
Returns: success code, if failure also defending move
* genmove_black: Generate and play the supposedly best black move.
Returns: a move coordinate or "PASS"
Status: Obsolete GTP version 1 command.
* genmove_white: Generate and play the supposedly best white move.
Returns: a move coordinate or "PASS"
Status: Obsolete GTP version 1 command.
* genmove: Generate and play the supposedly best move for either
Returns: a move coordinate or "PASS" (or "resign" if resignation_allowed)
Status: GTP version 2 standard command.
* reg_genmove: Generate the supposedly best move for either color.
Returns: a move coordinate (or "PASS")
Status: GTP version 2 standard command.
* gg_genmove: Generate the supposedly best move for either color.
Arguments: color to move, optionally a random seed
Returns: a move coordinate (or "PASS")
This differs from reg_genmove in the optional random seed.
* restricted_genmove: Generate the supposedly best move for either
color from a choice of allowed vertices.
Arguments: color to move, allowed vertices
Fails: invalid color, invalid vertex, no vertex listed
Returns: a move coordinate (or "PASS")
* kgs-genmove_cleanup: Generate and play the supposedly best move
for either color, not passing until all dead opponent stones have
Returns: a move coordinate (or "PASS")
Status: KGS specific command.
A similar command, but possibly somewhat different, will likely be added
to GTP version 3 at a later time.
* level: Set the playing level.
Fails: incorrect argument
Fails: If move history is too short.
Status: GTP version 2 standard command.
* gg-undo: Undo a number of moves
Fails: If move history is too short.
* time_settings: Set time allowance
Arguments: int main_time, int byo_yomi_time, int byo_yomi_stones
Status: GTP version 2 standard command.
* time_left: Report remaining time
Arguments: color color, int time, int stones
Status: GTP version 2 standard command.
* final_score: Compute the score of a finished game.
Arguments: Optional random seed
Returns: Score in SGF format (RE property).
Status: GTP version 2 standard command.
* final_status: Report the final status of a vertex in a finished
Arguments: Vertex, optional random seed
Returns: Status in the form of one of the strings "alive", "dead",
"seki", "white_territory", "black_territory", or "dame".
* final_status_list: Report vertices with a specific final status in
Arguments: Status in the form of one of the strings "alive", "dead",
"seki", "white_territory", "black_territory", or "dame".
An optional random seed can be added.
Fails: missing or invalid status string
Returns: Vertices having the specified status. These are split with
one string on each line if the vertices are nonempty (i.e.
for "alive", "dead", and "seki").
Status: GTP version 2 standard command.
However, "dame", "white_territory", and "black_territory"
* estimate_score: Estimate the score
Returns: upper and lower bounds for the score
* experimental_score: Estimate the score, taking into account which
This function generates a move for color, then adds the
value of the move generated to the value of the position.
Critical dragons are awarded to the opponent since the
value of rescuing a critical dragon is taken into account
in the value of the move generated.
* reset_life_node_counter: Reset the count of life nodes.
Note: This function is obsolete and only remains for backwards
* get_life_node_counter: Retrieve the count of life nodes.
Returns: number of life nodes
Note: This function is obsolete and only remains for backwards
* reset_owl_node_counter: Reset the count of owl nodes.
* get_owl_node_counter: Retrieve the count of owl nodes.
Returns: number of owl nodes
* reset_reading_node_counter: Reset the count of reading nodes.
* get_reading_node_counter: Retrieve the count of reading nodes.
Returns: number of reading nodes
* reset_trymove_counter: Reset the count of trymoves/trykos.
* get_trymove_counter: Retrieve the count of trymoves/trykos.
Returns: number of trymoves/trykos
* reset_connection_node_counter: Reset the count of connection nodes.
* get_connection_node_counter: Retrieve the count of connection
Returns: number of connection nodes
* test_eyeshape: Test an eyeshape for inconsistent evaluations
Arguments: Eyeshape vertices
Returns: Failure reports on stderr.
* analyze_eyegraph: Compute an eyevalue and vital points for an eye
Arguments: Eyeshape encoded in string
Fails: Bad eyeshape, analysis failed
Returns: Eyevalue, vital points
* cputime: Returns elapsed CPU time in seconds.
Returns: Total elapsed (user + system) CPU time in seconds.
* showboard: Write the position to stdout.
Status: GTP version 2 standard command.
* dump_stack: Dump stack to stderr.
* initial_influence: Return information about the initial influence
Arguments: color to move, what information
Returns: Influence data formatted like:
0.51 1.34 3.20 6.60 9.09 8.06 1.96 0.00 0.00
0.45 1.65 4.92 12.19 17.47 15.92 4.03 0.00 0.00
0.00 0.00 0.00 0.00 0.00 100.00 75.53 41.47 23.41
The available choices of information are:
white_attenuation (float)
black_attenuation (float)
white_permeability (float)
black_permeability (float)
The encoding of influence_regions is as follows:
* move_influence: Return information about the influence function
Arguments: move, what information
Returns: Influence data formatted like for initial_influence.
* move_probabilities: List probabilities of each move being played
(when non-zero). If no previous genmove command has been issued,
the result of this command will be meaningless.
Returns: Move, probabilty pairs, one per row.
* move_uncertainty: Return the number of bits of uncertainty in the
move. If no previous genmove command has been issued, the result
of this command will be meaningless.
Returns: bits of uncertainty
* followup_influence: Return information about the followup
Arguments: move, what information
Returns: Influence data formatted like for initial_influence.
* worm_data: Return the information in the worm data structure.
Arguments: optional vertex
Returns: Worm data formatted like:
If an intersection is specified, only data for this one will be returned.
* worm_stones: List the stones of a worm
Arguments: the location, "BLACK" or "WHITE"
Fails: if called on an empty or off-board location
* worm_cutstone: Return the cutstone field in the worm data
Arguments: non-empty vertex
* dragon_data: Return the information in the dragon data structure.
Arguments: optional intersection
Returns: Dragon data formatted in the corresponding way to worm_data.
* dragon_stones: List the stones of a dragon
Fails: if called on an empty or off-board location
* eye_data: Return the information in the eye data structure.
Returns: eye data fields and values, one pair per row
* half_eye_data: Return the information in the half eye data
Returns: half eye data fields and values, one pair per row
* start_sgftrace: Start storing moves executed during reading in an
Warning: You had better know what you're doing if you try to use this
* finish_sgftrace: Finish storing moves in an sgf tree and write it
Warning: You had better know what you're doing if you try to use this
* printsgf: Dump the current position as a static sgf file to
filename, or as output if filename is missing or "-"
Arguments: optional filename
Returns: nothing if filename, otherwise the sgf
* tune_move_ordering: Tune the parameters for the move ordering in
Arguments: MOVE_ORDERING_PARAMETERS integers
Fails: incorrect arguments
* echo: Echo the parameter
* echo_err: Echo the parameter to stdout AND stderr
* help: List all known commands
Returns: list of known commands, one per line
Status: GTP version 2 standard command.
* known_command: Tell whether a command is known.
Returns: "true" if command exists, "false" if not
Status: GTP version 2 standard command.
* report_uncertainty: Turn uncertainty reports from owl_attack and
* get_random_seed: Get the random seed
* set_random_seed: Set the random seed
* advance_random_seed: Advance the random seed by a number of games.
Returns: New random seed.
* is_surrounded: Determine if a dragon is surrounded
Arguments: vertex (dragon)
Fails: invalid vertex, empty vertex
Returns: 1 if surrounded, 2 if weakly surrounded, 0 if not
* does_surround: Determine if a move surrounds a dragon
Arguments: vertex (move), vertex (dragon)
Fails: invalid vertex, empty (dragon, nonempty (move)
Returns: 1 if (move) surrounds (dragon)
* surround_map: Report the surround map for dragon at a vertex
Arguments: vertex (dragon), vertex (mapped location)
Fails: invalid vertex, empty dragon
Returns: value of surround map at (mapped location), or -1 if
* set_search_diamond: limit search, and establish a search diamond
* reset_search_mask: unmark the entire board for limited search
* limit_search: sets the global variable limit_search
* set_search_limit: mark a vertex for limited search
* draw_search_area: Draw search area. Writes to stderr.
File: gnugo.info, Node: Regression, Next: Copying, Prev: GTP, Up: Top
The standard purpose of regression testing is to avoid getting the same
bug twice. When a bug is found, the programmer fixes the bug and adds a
test to the test suite. The test should fail before the fix and pass
after the fix. When a new version is about to be released, all the tests
in the regression test suite are run and if an old bug reappears, this
will be seen quickly since the appropriate test will fail.
The regression testing in GNU Go is slightly different. A typical
test case involves specifying a position and asking the engine what
move it would make. This is compared to one or more correct moves to
decide whether the test case passes or fails. It is also stored whether
a test case is expected to pass or fail, and deviations in this status
signify whether a change has solved some problem and/or broken something
else. Thus the regression tests both include positions highlighting some
mistake being done by the engine, which are waiting to be fixed, and
positions where the engine does the right thing, where we want to detect
if a change breaks something.
* Regression Testing:: Regression Testing in GNU Go
* Test Suites:: Test Suites
* Running the Regressions:: Running the Regression Tests
* Running regress.pike:: Running regress.pike
* Viewing with Emacs:: Viewing tests with Emacs
* HTML Views:: HTML Views
File: gnugo.info, Node: Regression Testing, Next: Test Suites, Up: Regression
20.1 Regression testing in GNU Go
=================================
Regression testing is performed by the files in the `regression/'
directory. The tests are specified as GTP commands in files with the
suffix `.tst', with corresponding correct results and expected
pass/fail status encoded in GTP comments following the test. To run a
test suite the shell scripts `test.sh', `eval.sh', and `regress.sh' can
be used. There are also Makefile targets to do this. If you `make
all_batches' most of the tests are run. The Pike script `regress.pike'
can also be used to run all tests or a subset of the tests.
Game records used by the regression tests are stored in the
directory `regression/games/' and its subdirectories.
File: gnugo.info, Node: Test Suites, Next: Running the Regressions, Prev: Regression Testing, Up: Regression
The regression tests are grouped into suites and stored in files as GTP
commands. A part of a test suite can look as follows:
# Connecting with ko at B14 looks best. Cutting at D17 might be
# considered. B17 (game move) is inferior.
loadsgf games/strategy25.sgf 61
# The game move at P13 is a suicidal blunder.
loadsgf games/strategy25.sgf 249
loadsgf games/strategy26.sgf 257
Lines starting with a hash sign, or in general anything following a
hash sign, are interpreted as comments by the GTP mode and thus ignored
by the engine. GTP commands are executed in the order they appear, but
only those on numbered lines are used for testing. The comment lines
starting with `#?' are magical to the regression testing scripts and
indicate correct results and expected pass/fail status. The string
within brackets is matched as a regular expression against the response
from the previous numbered GTP command. A particular useful feature of
regular expressions is that by using `|' it is possible to specify
alternatives. Thus `B14|D17' above means that if either `B14' or `D17'
is the move generated in test case 90, it passes. There is one
important special case to be aware of. If the correct result string
starts with an exclamation mark, this is excluded from the regular
expression but afterwards the result of the matching is negated. Thus
`!P13' in test case 95 means that any move except `P13' is accepted as
In test case 100, the brackets on the `#?' line is followed by an
asterisk. This means that the test is expected to fail. If there is no
asterisk, the test is expected to pass. The brackets may also be
followed by a `&', meaning that the result is ignored. This is
primarily used to report statistics, e.g. how many tactical reading
nodes were spent while running the test suite.
File: gnugo.info, Node: Running the Regressions, Next: Running regress.pike, Prev: Test Suites, Up: Regression
20.3 Running the Regression Tests
=================================
`./test.sh blunder.tst' runs the tests in `blunder.tst' and prints the
results of the commands on numbered lines, which may look like:
This is usually not very informative, however. More interesting is
`./eval.sh blunder.tst' which also compares the results above against
the correct ones in the test file and prints a report for each test on
1 failed: Correct '!E5', got 'E5'
2 failed: Correct 'C9|H9', got 'F9'
4 failed: Correct 'B5|C5|C4|D4|E4|E3|F3', got 'B7'
6 failed: Correct 'D4', got 'E4'
8 failed: Correct 'B4', got 'A3'
9 failed: Correct 'G8|G9|H8', got 'D9'
10 failed: Correct 'G9|F9|C7', got 'J9'
11 failed: Correct 'D4|E4|E5|F4|C6', got 'B3'
12 failed: Correct 'D4', got 'C6'
13 failed: Correct 'D4|E4|E5|F4', got 'C6'
The result of a test can be one of four different cases:
* `passed': An expected pass
This is the ideal result.
* `PASSED': An unexpected pass
This is a result that we are hoping for when we fix a bug. An old
test case that used to fail is now passing.
* `failed': An expected failure
The test failed but this was also what we expected, unless we were
trying to fix the particular mistake highlighted by the test case.
These tests show weaknesses of the GNU Go engine and are good
places to search if you want to detect an area which needs
* `FAILED': An unexpected failure
This should nominally only happen if something is broken by a
change. However, sometimes GNU Go passes a test, but for the wrong
reason or for a combination of wrong reasons. When one of these
reasons is fixed, the other one may shine through so that the test
suddenly fails. When a test case unexpectedly fails, it is
necessary to make a closer examination in order to determine
whether a change has broken something.
If you want a less verbose report, `./regress.sh . blunder.tst' does
the same thing as the previous command, but only reports unexpected
results. The example above is compressed to
For convenience the tests are also available as makefile targets. For
example, `make blunder' runs the tests in the blunder test suite by
executing `eval.sh blunder.tst'. `make all_batches' runs all test
suites in a sequence using the `regress.sh' script.
File: gnugo.info, Node: Running regress.pike, Next: Viewing with Emacs, Prev: Running the Regressions, Up: Regression
20.4 Running regress.pike
=========================
A more powerful way to run regressions is with the script
`regress.pike'. This requires that you have Pike
(`http://pike.ida.liu.se') installed.
Executing `./regress.pike' without arguments will run all testsuites
that `make all_batches' would run. The difference is that unexpected
results are reported immediately when they have been found (instead of
after the whole file has been run) and that statistics of time
consumption and node usage is presented for each test file and in total.
To run a single test suite do e.g. `./regress.pike nicklas3.tst' or
`./regress.pike nicklas3'. The result may look like:
nicklas3 2.96 614772 3322 469
Total nodes: 614772 3322 469
The numbers here mean that the test suite took 2.96 seconds of
processor time and 3.22 seconds of real time. The consumption of
reading nodes was 614772 for tactical reading, 3322 for owl reading,
and 469 for connection reading. The last line relates to the
variability of the generated moves in the test suite, and 0 means that
none was decided by the randomness contribution to the move valuation.
Multiple testsuites can be run by e.g. `./regress.pike owl ld_owl owl1'.
It is also possible to run a single testcase, e.g. `./regress.pike
strategy:6', a number of testcases, e.g. `./regress.pike
strategy:6,23,45', a range of testcases, e.g. `./regress.pike
strategy:13-15' or more complex combinations e.g. `./regress.pike
strategy:6,13-15,23,45 nicklas3:602,1403'.
There are also command line options to choose what engine to run,
what options to send to the engine, to turn on verbose output, and to
use a file to specify which testcases to run. Run `./regress.pike
--help' for a complete and up to date list of options.
File: gnugo.info, Node: Viewing with Emacs, Next: HTML Views, Prev: Running regress.pike, Up: Regression
20.5 Viewing tests with Emacs
=============================
To get a quick regression view, you may use the graphical display mode
available with Emacs (*note Emacs::). You will want the cursor in the
regression buffer when you enter `M-x gnugo', so that GNU Go opens in
the correct directory. A good way to be in the right directory is to
open the window of the test you want to investigate. Then you can cut
and past GTP commands directly from the test to the minibuffer, using
the `:' command from Emacs. Although Emacs mode does not have a
coordinate grid, you may get an ascii board with the coordinate grid
using `: showboard' command.
File: gnugo.info, Node: HTML Views, Prev: Viewing with Emacs, Up: Regression
20.6 HTML Regression Views
==========================
Extremely useful HTML Views of the regression tests may be produced
using two perl scripts `regression/regress.pl' and
`regression/regress.plx'.
1. The driver program (regress.pl) which:
* Runs the regression tests, invoking GNU Go.
* Captures the trace output, board position, and pass/fail
status, sgf output, and dragon status information.
2. The interface to view the captured output (regress.plx) which:
* Displays the captured output in helpful formats (i.e. HTML).
20.6.1 Setting up the HTML regression Views
-------------------------------------------
There are many ways configuring Apache to permit CGI scripts, all of
them are featured in Apache documentation, which can be found at
`http://httpd.apache.org/docs/2.0/howto/cgi.html'
Below you will find one example.
This documentation assumes an Apache 2.0 included in Fedora Core
distribution, but it should be fairly close to the config for other
First, you will need to configure Apache to run CGI scripts in the
directory you wish to serve the html views from. In
`/etc/httpd/conf/httpd.conf' there should be a line:
`DocumentRoot "/var/www/html"'
Search for a line `<Directory "/path/to/directory">', where
`/path/to/directory' is the same as provided in `DocumentRoot', then
add `ExecCGI' to list of `Options'. The whole section should look like:
<Directory "/var/www/html">
This allows CGI scripts to be executed in the directory used by
regress.plx. Next, you need to tell Apache that `.plx' is a CGI script
ending. Your `httpd.conf' file should contain a line:
`AddHandler cgi-script ...'
If there isn't already, add it; add `.plx' to the list of extensions,
so line should look like:
`AddHandler cgi-script ... .plx'
You will also need to make sure you have the necessary modules
loaded to run CGI scripts; mod_cgi and mod_mime should be sufficient.
Your `httpd.conf' should have the relevant `LoadModule cgi_module
modules/mod_cgi.so' and `LoadModule mime_module modules/mod_mime.so'
lines; uncomment them if necessary.
Next, you need to put a copy of `regress.plx' in the `DocumentRoot'
directory `/var/www/html' or it subdirectories where you plan to serve
You will also need to install the Perl module GD
(`http://search.cpan.org/dist/GD/'), available from CPAN.
Finally, run `regression/regress.pl' to create the xml data used to
generate the html views (to do all regression tests run
`regression/regress.pl -a 1'); then, copy the `html/' directory to the
same directory as `regress.plx' resides in.
At this point, you should have a working copy of the html regression
Additional notes for Debian users: The Perl GD module can be
installed by `apt-get install libgd-perl'. It may suffice to add this to
the apache2 configuration:
<Directory "/var/www/regression">
AddHandler cgi-script .plx
RedirectMatch ^/regression$ /regression/regress.plx
and then make a link from `/var/www/regression' to the GNU Go
regression directory. The `RedirectMatch' statement is only needed to
set up a shorter entry URL.
File: gnugo.info, Node: Copying, Next: Concept Index, Prev: Regression, Up: Top
The program GNU Go is distributed under the terms of the GNU General
Public License (GPL). Its documentation is distributed under the terms
of the GNU Free Documentation License (GFDL).
* GPL:: The GNU General Public License
* GFDL:: The GNU Free Documentation License
* GTP License:: The Go Text Protocol License
File: gnugo.info, Node: GPL, Next: GFDL, Prev: Copying, Up: Copying
A.1 GNU GENERAL PUBLIC LICENSE
==============================
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party that is in the business of distributing software, under
which you make payment to the third party based on the extent of
your activity of conveying the work, and under which the third
party grants, to any of the parties who would receive the covered
work from you, a discriminatory patent license (a) in connection
with copies of the covered work conveyed by you (or copies made
from those copies), or (b) primarily for and in connection with
specific products or compilations that contain the covered work,
unless you entered into that arrangement, or that patent license
was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting
any implied license or other defenses to infringement that may
otherwise be available to you under applicable patent law.
12. NO SURRENDER OF OTHERS' FREEDOM
If conditions are imposed on you (whether by court order,
agreement or otherwise) that contradict the conditions of this
License, they do not excuse you from the conditions of this
License. If you cannot convey a covered work so as to satisfy
simultaneously your obligations under this License and any other
pertinent obligations, then as a consequence you may not convey it
at all. For example, if you agree to terms that obligate you to
collect a royalty for further conveying from those to whom you
convey the Program, the only way you could satisfy both those
terms and this License would be to refrain entirely from conveying
13. USE WITH THE GNU AFFERO GENERAL PUBLIC LICENSE
Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU Affero General Public License into a
single combined work, and to convey the resulting work. The terms
of this License will continue to apply to the part which is the
covered work, but the special requirements of the GNU Affero
General Public License, section 13, concerning interaction through
a network will apply to the combination as such.
14. REVISED VERSIONS OF THIS LICENSE
The Free Software Foundation may publish revised and/or new
versions of the GNU General Public License from time to time.
Such new versions will be similar in spirit to the present
version, but may differ in detail to address new problems or
Each version is given a distinguishing version number. If the
Program specifies that a certain numbered version of the GNU
General Public License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that numbered version or of any later version published by the
Free Software Foundation. If the Program does not specify a
version number of the GNU General Public License, you may choose
any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future
versions of the GNU General Public License can be used, that
proxy's public statement of acceptance of a version permanently
authorizes you to choose that version for the Program.
Later license versions may give you additional or different
permissions. However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
15. DISCLAIMER OF WARRANTY
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE
RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
NECESSARY SERVICING, REPAIR OR CORRECTION.
16. LIMITATION OF LIABILITY.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU
FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
THE POSSIBILITY OF SUCH DAMAGES.
17. INTERPRETATION OF SECTIONS 15 AND 16
If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely
approximates an absolute waiver of all civil liability in
connection with the Program, unless a warranty or assumption of
liability accompanies a copy of the Program in return for a fee.
How to Apply These Terms to your New Programs
=============================================
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.
<one line to give the program's name and a brief idea of what it
does.> Copyright (C) <year> <name of author>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
Also add information on how to contact you by electronic and paper
If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:
<program> Copyright (C) <year> <name of author> This program
comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This
is free software, and you are welcome to redistribute it under
certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License. Of course, your
program's commands might be different; for a GUI interface, you would
You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. For more information on this, and how to apply and follow
the GNU GPL, see <http://www.gnu.org/licenses/>.
The GNU General Public License does not permit incorporating your
program into proprietary programs. If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use the
GNU Lesser General Public License instead of this License. But first,
please read <http://www.gnu.org/philosophy/why-not-lgpl.html>.
File: gnugo.info, Node: GFDL, Next: GTP License, Prev: GPL, Up: Copying
A.2 GNU FREE DOCUMENTATION LICENSE
==================================
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it
can be distributed under the terms of this License. Such a notice
grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You
accept the license if you copy, modify or distribute the work in a
way requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could
fall directly within that overall subject. (Thus, if the Document
is in part a textbook of mathematics, a Secondary Section may not
explain any mathematics.) The relationship could be a matter of
historical connection with the subject or with related matters, or
of legal, commercial, philosophical, ethical or political position
The "Invariant Sections" are certain Secondary Sections whose
titles are designated, as being those of Invariant Sections, in
the notice that says that the Document is released under this
License. If a section does not fit the above definition of
Secondary then it is not allowed to be designated as Invariant.
The Document may contain zero Invariant Sections. If the Document
does not identify any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are
listed, as Front-Cover Texts or Back-Cover Texts, in the notice
that says that the Document is released under this License. A
Front-Cover Text may be at most 5 words, and a Back-Cover Text may
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images
composed of pixels) generic paint programs or (for drawings) some
widely available drawing editor, and that is suitable for input to
text formatters or for automatic translation to a variety of
formats suitable for input to text formatters. A copy made in an
otherwise Transparent file format whose markup, or absence of
markup, has been arranged to thwart or discourage subsequent
modification by readers is not Transparent. An image format is
not Transparent if used for any substantial amount of text. A
copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available DTD, and
standard-conforming simple HTML, PostScript or PDF designed for
human modification. Examples of transparent image formats include
PNG, XCF and JPG. Opaque formats include proprietary formats that
can be read and edited only by proprietary word processors, SGML or
XML for which the DTD and/or processing tools are not generally
available, and the machine-generated HTML, PostScript or PDF
produced by some word processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the
material this License requires to appear in the title page. For
works in formats which do not have any title page as such, "Title
Page" means the text near the most prominent appearance of the
work's title, preceding the beginning of the body of the text.
The "publisher" means any person or entity that distributes copies
of the Document to the public.
A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
this License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow
the conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
Back-Cover Texts on the back cover. Both covers must also clearly
and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the
title equally prominent and visible. You may add other material
on the covers in addition. Copying with changes limited to the
covers, as long as they preserve the title of the Document and
satisfy these conditions, can be treated as verbatim copying in
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a
machine-readable Transparent copy along with each Opaque copy, or
state in or with each Opaque copy a computer-network location from
which the general network-using public has access to download
using public-standard network protocols a complete Transparent
copy of the Document, free of added material. If you use the
latter option, you must take reasonably prudent steps, when you
begin distribution of Opaque copies in quantity, to ensure that
this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you
distribute an Opaque copy (directly or through your agents or
retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of
copies, to give them a chance to provide you with an updated
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with
the Modified Version filling the role of the Document, thus
licensing distribution and modification of the Modified Version to
whoever possesses a copy of it. In addition, you must do these
things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of
previous versions (which should, if there were any, be listed
in the History section of the Document). You may use the
same title as a previous version if the original publisher of
that version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on
the Title Page. If there is no section Entitled "History" in
the Document, create one stating the title, year, authors,
and publisher of the Document as given on its Title Page,
then add an item describing the Modified Version as stated in
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in
the "History" section. You may omit a network location for a
work that was published at least four years before the
Document itself, or if the original publisher of the version
it refers to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the
section all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option
designate some or all of these sections as invariant. To do this,
add their titles to the list of Invariant Sections in the Modified
Version's license notice. These titles must be distinct from any
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text
has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end
of the list of Cover Texts in the Modified Version. Only one
passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the
Document already includes a cover text for the same cover,
previously added by you or by arrangement made by the same entity
you are acting on behalf of, you may not add another; but you may
replace the old one, on explicit permission from the previous
publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this
License give permission to use their names for publicity for or to
assert or imply endorsement of any Modified Version.
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination
all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the
documents in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of
a storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void,
and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your
license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly
and finally terminates your license, and (b) permanently, if the
copyright holder fails to notify you of the violation by some
reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from
that copyright holder, and you cure the violation prior to 30 days
after your receipt of the notice.
Termination of your rights under this section does not terminate
the licenses of parties who have received copies or rights from
you under this License. If your rights have been terminated and
not permanently reinstated, receipt of a copy of some or all of
the same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
`http://www.gnu.org/copyleft/'.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If
the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the
Free Software Foundation. If the Document specifies that a proxy
can decide which future versions of this License can be used, that
proxy's public statement of acceptance of a version permanently
authorizes you to choose that version for the Document.
"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server.
A "Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this
License somewhere other than this MMC, and subsequently
incorporated in whole or in part into the MMC, (1) had no cover
texts or invariant sections, and (2) were thus incorporated prior
The operator of an MMC Site may republish an MMC contained in the
site under CC-BY-SA on the same site at any time before August 1,
2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.
File: gnugo.info, Node: GTP License, Prev: GFDL, Up: Copying
A.3 The Go Text Protocol License
================================
In order to facilitate the use of the Go Text Protocol, the two files
`gtp.c' and `gtp.h' are licensed under the following terms.
Copyright 2001 by the Free Software Foundation.
Permission is hereby granted, free of charge, to any person
obtaining a copy of this file `gtp.x', to deal in the Software without
restriction, including without limitation the rights to use, copy,
modify, merge, publish, distribute, and/or sell copies of the Software,
and to permit persons to whom the Software is furnished to do so,
provided that the above copyright notice(s) and this permission notice
appear in all copies of the Software and that both the above copyright
notice(s) and this permission notice appear in supporting documentation.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
OF THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
HOLDERS INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL
INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING
FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
Except as contained in this notice, the name of a copyright holder
shall not be used in advertising or otherwise to promote the sale, use
or other dealings in this Software without prior written authorization
File: gnugo.info, Node: Concept Index, Next: Functions Index, Prev: Copying, Up: Top
projects / sgk-go / blob