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annotate Lib/whrandom.py @ 5817:48b94de85bf3 legacy-trunk

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author Guido van Rossum <guido@python.org>
date Thu, 17 Jul 1997 16:29:42 +0000
parents 4b42eea10a02
children 48df2080d7d4
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1 # WICHMANN-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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15 #
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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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27
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28 # Translated by Guido van Rossum from C source provided by
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29 # Adrian Baddeley.
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30
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31
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32 class whrandom:
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33 #
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34 # Initialize an instance.
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35 # Without arguments, initialize from current time.
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36 # With arguments (x, y, z), initialize from them.
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37 #
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38 def __init__(self, x = 0, y = 0, z = 0):
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39 self.seed(x, y, z)
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40 #
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41 # Set the seed from (x, y, z).
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42 # These must be integers in the range [0, 256).
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43 #
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44 def seed(self, x = 0, y = 0, z = 0):
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45 if not type(x) == type(y) == type(z) == type(0):
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46 raise TypeError, 'seeds must be integers'
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47 if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256):
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48 raise ValueError, 'seeds must be in range(0, 256)'
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49 if 0 == x == y == z:
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50 # Initialize from current time
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51 import time
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52 t = long(time.time() * 256)
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53 t = int((t&0xffffff) | (t>>24))
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54 t, x = divmod(t, 256)
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55 t, y = divmod(t, 256)
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56 t, z = divmod(t, 256)
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57 # Zero is a poor seed, so substitute 1
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58 self._seed = (x or 1, y or 1, z or 1)
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59 #
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60 # Get the next random number in the range [0.0, 1.0).
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61 #
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62 def random(self):
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63 x, y, z = self._seed
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64 #
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65 x = (171 * x) % 30269
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66 y = (172 * y) % 30307
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67 z = (170 * z) % 30323
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68 #
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69 self._seed = x, y, z
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70 #
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71 return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0
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72 #
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73 # Get a random number in the range [a, b).
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74 #
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75 def uniform(self, a, b):
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76 return a + (b-a) * self.random()
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77 #
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78 # Get a random integer in the range [a, b] including both end points.
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79 #
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80 def randint(self, a, b):
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81 return a + int(self.random() * (b+1-a))
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82 #
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83 # Choose a random element from a non-empty sequence.
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84 #
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85 def choice(self, seq):
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86 return seq[int(self.random() * len(seq))]
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88
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89 # Initialize from the current time
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90 #
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91 _inst = whrandom()
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92 seed = _inst.seed
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93 random = _inst.random
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94 uniform = _inst.uniform
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95 randint = _inst.randint
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96 choice = _inst.choice