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1 | """Wichman-Hill random number generator. |
2 | ||
3 | Wichmann, B. A. & Hill, I. D. (1982) | |
4 | Algorithm AS 183: | |
5 | An efficient and portable pseudo-random number generator | |
6 | Applied Statistics 31 (1982) 188-190 | |
7 | ||
8 | see also: | |
9 | Correction to Algorithm AS 183 | |
10 | Applied Statistics 33 (1984) 123 | |
11 | ||
12 | McLeod, A. I. (1985) | |
13 | A remark on Algorithm AS 183 | |
14 | Applied Statistics 34 (1985),198-200 | |
15 | ||
16 | ||
17 | USE: | |
18 | whrandom.random() yields double precision random numbers | |
19 | uniformly distributed between 0 and 1. | |
20 | ||
21 | whrandom.seed(x, y, z) must be called before whrandom.random() | |
22 | to seed the generator | |
23 | ||
24 | There is also an interface to create multiple independent | |
25 | random generators, and to choose from other ranges. | |
26 | ||
27 | ||
28 | ||
29 | Multi-threading note: the random number generator used here is not | |
30 | thread-safe; it is possible that nearly simultaneous calls in | |
31 | different theads return the same random value. To avoid this, you | |
32 | have to use a lock around all calls. (I didn't want to slow this | |
33 | down in the serial case by using a lock here.) | |
34 | """ | |
35 | ||
36 | import warnings | |
37 | warnings.warn("the whrandom module is deprecated; please use the random module", | |
38 | DeprecationWarning) | |
39 | ||
40 | # Translated by Guido van Rossum from C source provided by | |
41 | # Adrian Baddeley. | |
42 | ||
43 | ||
44 | class whrandom: | |
45 | def __init__(self, x = 0, y = 0, z = 0): | |
46 | """Initialize an instance. | |
47 | Without arguments, initialize from current time. | |
48 | With arguments (x, y, z), initialize from them.""" | |
49 | self.seed(x, y, z) | |
50 | ||
51 | def seed(self, x = 0, y = 0, z = 0): | |
52 | """Set the seed from (x, y, z). | |
53 | These must be integers in the range [0, 256).""" | |
54 | if not type(x) == type(y) == type(z) == type(0): | |
55 | raise TypeError, 'seeds must be integers' | |
56 | if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256): | |
57 | raise ValueError, 'seeds must be in range(0, 256)' | |
58 | if 0 == x == y == z: | |
59 | # Initialize from current time | |
60 | import time | |
61 | t = long(time.time() * 256) | |
62 | t = int((t&0xffffff) ^ (t>>24)) | |
63 | t, x = divmod(t, 256) | |
64 | t, y = divmod(t, 256) | |
65 | t, z = divmod(t, 256) | |
66 | # Zero is a poor seed, so substitute 1 | |
67 | self._seed = (x or 1, y or 1, z or 1) | |
68 | ||
69 | def random(self): | |
70 | """Get the next random number in the range [0.0, 1.0).""" | |
71 | # This part is thread-unsafe: | |
72 | # BEGIN CRITICAL SECTION | |
73 | x, y, z = self._seed | |
74 | # | |
75 | x = (171 * x) % 30269 | |
76 | y = (172 * y) % 30307 | |
77 | z = (170 * z) % 30323 | |
78 | # | |
79 | self._seed = x, y, z | |
80 | # END CRITICAL SECTION | |
81 | # | |
82 | return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0 | |
83 | ||
84 | def uniform(self, a, b): | |
85 | """Get a random number in the range [a, b).""" | |
86 | return a + (b-a) * self.random() | |
87 | ||
88 | def randint(self, a, b): | |
89 | """Get a random integer in the range [a, b] including | |
90 | both end points. | |
91 | ||
92 | (Deprecated; use randrange below.)""" | |
93 | return self.randrange(a, b+1) | |
94 | ||
95 | def choice(self, seq): | |
96 | """Choose a random element from a non-empty sequence.""" | |
97 | return seq[int(self.random() * len(seq))] | |
98 | ||
99 | def randrange(self, start, stop=None, step=1, int=int, default=None): | |
100 | """Choose a random item from range(start, stop[, step]). | |
101 | ||
102 | This fixes the problem with randint() which includes the | |
103 | endpoint; in Python this is usually not what you want. | |
104 | Do not supply the 'int' and 'default' arguments.""" | |
105 | # This code is a bit messy to make it fast for the | |
106 | # common case while still doing adequate error checking | |
107 | istart = int(start) | |
108 | if istart != start: | |
109 | raise ValueError, "non-integer arg 1 for randrange()" | |
110 | if stop is default: | |
111 | if istart > 0: | |
112 | return int(self.random() * istart) | |
113 | raise ValueError, "empty range for randrange()" | |
114 | istop = int(stop) | |
115 | if istop != stop: | |
116 | raise ValueError, "non-integer stop for randrange()" | |
117 | if step == 1: | |
118 | if istart < istop: | |
119 | return istart + int(self.random() * | |
120 | (istop - istart)) | |
121 | raise ValueError, "empty range for randrange()" | |
122 | istep = int(step) | |
123 | if istep != step: | |
124 | raise ValueError, "non-integer step for randrange()" | |
125 | if istep > 0: | |
126 | n = (istop - istart + istep - 1) / istep | |
127 | elif istep < 0: | |
128 | n = (istop - istart + istep + 1) / istep | |
129 | else: | |
130 | raise ValueError, "zero step for randrange()" | |
131 | ||
132 | if n <= 0: | |
133 | raise ValueError, "empty range for randrange()" | |
134 | return istart + istep*int(self.random() * n) | |
135 | ||
136 | ||
137 | # Initialize from the current time | |
138 | _inst = whrandom() | |
139 | seed = _inst.seed | |
140 | random = _inst.random | |
141 | uniform = _inst.uniform | |
142 | randint = _inst.randint | |
143 | choice = _inst.choice | |
144 | randrange = _inst.randrange |