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.\" @(#)random.3 6.5 (Berkeley) 4/19/91
.Nd better random number generator; routines for changing generators
.Fn srandom "unsigned seed"
.Fn initstate "unsigned seed" "char *state" "int n"
.Fn setstate "char *state"
uses a non-linear additive feedback random number generator employing a
default table of size 31 long integers to return successive pseudo-random
numbers in the range from 0 to
.if t 2\u\s731\s10\d\(mi1.
The period of this random number generator is very large, approximately
.if t 16\(mu(2\u\s731\s10\d\(mi1).
.Fn random Ns / Fn srandom
have (almost) the same calling sequence and initialization properties as
.Xr rand 3 Ns / Xr srand 3 .
produces a much less random sequence \(em in fact, the low dozen bits
generated by rand go through a cyclic pattern. All the bits generated by
will produce a random binary
does not return the old seed; the reason for this is that the amount of
state information used is much more than a single word. (Two other
routines are provided to deal with restarting/changing random
will by default produce a sequence of numbers that can be duplicated
routine allows a state array, passed in as an argument, to be initialized
for future use. The size of the state array (in bytes) is used by
to decide how sophisticated a random number generator it should use \(em the
more state, the better the random numbers will be.
(Current "optimal" values for the amount of state information are
8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
the nearest known amount. Using less than 8 bytes will cause an error.)
The seed for the initialization (which specifies a starting point for
the random number sequence, and provides for restarting at the same
point) is also an argument.
returns a pointer to the previous state information array.
Once a state has been initialized, the
routine provides for rapid switching between states.
returns a pointer to the previous state array; its
argument state array is used for further random number generation
Once a state array has been initialized, it may be restarted at a
different point either by calling
(with the desired seed, the state array, and its size) or by calling
(with the state array) and
The advantage of calling both
is that the size of the state array does not have to be remembered after
With 256 bytes of state information, the period of the random number
generator is greater than
which should be sufficient for most purposes.
is called with less than 8 bytes of state information, or if
detects that the state information has been garbled, error
messages are printed on the standard error output.