Mercurial > cpython-lru_cache-weakref

annotate Lib/whrandom.py @ 25838:8540887bcec6 2.2

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Backport of 2.183: Fix memory leak in add_subclass() found by NealN with valgrind.
author Guido van Rossum <guido@python.org>
date Fri, 18 Oct 2002 13:42:21 +0000
parents 4c01ee0a8073
children e23381fa4750
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1 """Wichman-Hill random number generator.
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2
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3 Wichmann, B. A. & Hill, I. D. (1982)
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4 Algorithm AS 183:
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5 An efficient and portable pseudo-random number generator
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6 Applied Statistics 31 (1982) 188-190
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7
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8 see also:
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9 Correction to Algorithm AS 183
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10 Applied Statistics 33 (1984) 123
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11
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12 McLeod, A. I. (1985)
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13 A remark on Algorithm AS 183
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14 Applied Statistics 34 (1985),198-200
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16
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17 USE:
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18 whrandom.random() yields double precision random numbers
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19 uniformly distributed between 0 and 1.
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20
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21 whrandom.seed(x, y, z) must be called before whrandom.random()
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22 to seed the generator
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23
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24 There is also an interface to create multiple independent
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25 random generators, and to choose from other ranges.
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29 Multi-threading note: the random number generator used here is not
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30 thread-safe; it is possible that nearly simultaneous calls in
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31 different theads return the same random value. To avoid this, you
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32 have to use a lock around all calls. (I didn't want to slow this
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33 down in the serial case by using a lock here.)
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34 """
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35
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36 # Translated by Guido van Rossum from C source provided by
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37 # Adrian Baddeley.
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38
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39
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40 class whrandom:
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41 def __init__(self, x = 0, y = 0, z = 0):
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42 """Initialize an instance.
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43 Without arguments, initialize from current time.
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44 With arguments (x, y, z), initialize from them."""
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45 self.seed(x, y, z)
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46
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47 def seed(self, x = 0, y = 0, z = 0):
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48 """Set the seed from (x, y, z).
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49 These must be integers in the range [0, 256)."""
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50 if not type(x) == type(y) == type(z) == type(0):
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51 raise TypeError, 'seeds must be integers'
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52 if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256):
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53 raise ValueError, 'seeds must be in range(0, 256)'
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54 if 0 == x == y == z:
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55 # Initialize from current time
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56 import time
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57 t = long(time.time() * 256)
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58 t = int((t&0xffffff) ^ (t>>24))
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59 t, x = divmod(t, 256)
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60 t, y = divmod(t, 256)
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61 t, z = divmod(t, 256)
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62 # Zero is a poor seed, so substitute 1
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63 self._seed = (x or 1, y or 1, z or 1)
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64
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65 def random(self):
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66 """Get the next random number in the range [0.0, 1.0)."""
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67 # This part is thread-unsafe:
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68 # BEGIN CRITICAL SECTION
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69 x, y, z = self._seed
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70 #
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71 x = (171 * x) % 30269
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72 y = (172 * y) % 30307
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73 z = (170 * z) % 30323
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74 #
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75 self._seed = x, y, z
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76 # END CRITICAL SECTION
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77 #
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78 return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0
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79
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80 def uniform(self, a, b):
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81 """Get a random number in the range [a, b)."""
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82 return a + (b-a) * self.random()
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83
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84 def randint(self, a, b):
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85 """Get a random integer in the range [a, b] including
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86 both end points.
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87
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88 (Deprecated; use randrange below.)"""
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89 return self.randrange(a, b+1)
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90
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91 def choice(self, seq):
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92 """Choose a random element from a non-empty sequence."""
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93 return seq[int(self.random() * len(seq))]
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94
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95 def randrange(self, start, stop=None, step=1, int=int, default=None):
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96 """Choose a random item from range(start, stop[, step]).
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97
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98 This fixes the problem with randint() which includes the
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99 endpoint; in Python this is usually not what you want.
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100 Do not supply the 'int' and 'default' arguments."""
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101 # This code is a bit messy to make it fast for the
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102 # common case while still doing adequate error checking
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103 istart = int(start)
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104 if istart != start:
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105 raise ValueError, "non-integer arg 1 for randrange()"
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106 if stop is default:
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107 if istart > 0:
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108 return int(self.random() * istart)
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109 raise ValueError, "empty range for randrange()"
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110 istop = int(stop)
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111 if istop != stop:
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112 raise ValueError, "non-integer stop for randrange()"
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113 if step == 1:
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114 if istart < istop:
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115 return istart + int(self.random() *
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116 (istop - istart))
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117 raise ValueError, "empty range for randrange()"
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118 istep = int(step)
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119 if istep != step:
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120 raise ValueError, "non-integer step for randrange()"
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121 if istep > 0:
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122 n = (istop - istart + istep - 1) / istep
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123 elif istep < 0:
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124 n = (istop - istart + istep + 1) / istep
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125 else:
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126 raise ValueError, "zero step for randrange()"
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127
15874
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128 if n <= 0:
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129 raise ValueError, "empty range for randrange()"
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130 return istart + istep*int(self.random() * n)
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131
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132
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133 # Initialize from the current time
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134 _inst = whrandom()
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135 seed = _inst.seed
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136 random = _inst.random
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137 uniform = _inst.uniform
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138 randint = _inst.randint
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139 choice = _inst.choice
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140 randrange = _inst.randrange