diff options
Diffstat (limited to 'Lib/whrandom.py')
| -rw-r--r-- | Lib/whrandom.py | 125 |
1 files changed, 58 insertions, 67 deletions
diff --git a/Lib/whrandom.py b/Lib/whrandom.py index 7f8fc60..fd9b1a9 100644 --- a/Lib/whrandom.py +++ b/Lib/whrandom.py @@ -1,54 +1,52 @@ -# WICHMANN-HILL RANDOM NUMBER GENERATOR -# -# Wichmann, B. A. & Hill, I. D. (1982) -# Algorithm AS 183: -# An efficient and portable pseudo-random number generator -# Applied Statistics 31 (1982) 188-190 -# -# see also: -# Correction to Algorithm AS 183 -# Applied Statistics 33 (1984) 123 -# -# McLeod, A. I. (1985) -# A remark on Algorithm AS 183 -# Applied Statistics 34 (1985),198-200 -# -# -# USE: -# whrandom.random() yields double precision random numbers -# uniformly distributed between 0 and 1. -# -# whrandom.seed(x, y, z) must be called before whrandom.random() -# to seed the generator -# -# There is also an interface to create multiple independent -# random generators, and to choose from other ranges. - - -# Translated by Guido van Rossum from C source provided by -# Adrian Baddeley. - - -# Multi-threading note: the random number generator used here is not -# thread-safe; it is possible that nearly simultaneous calls in -# different theads return the same random value. To avoid this, you -# have to use a lock around all calls. (I didn't want to slow this -# down in the serial case by using a lock here.) +"""Wichman-Hill random number generator. +Wichmann, B. A. & Hill, I. D. (1982) +Algorithm AS 183: +An efficient and portable pseudo-random number generator +Applied Statistics 31 (1982) 188-190 + +see also: + Correction to Algorithm AS 183 + Applied Statistics 33 (1984) 123 + + McLeod, A. I. (1985) + A remark on Algorithm AS 183 + Applied Statistics 34 (1985),198-200 + + +USE: +whrandom.random() yields double precision random numbers + uniformly distributed between 0 and 1. + +whrandom.seed(x, y, z) must be called before whrandom.random() + to seed the generator + +There is also an interface to create multiple independent +random generators, and to choose from other ranges. + + +Translated by Guido van Rossum from C source provided by +Adrian Baddeley. + + + +Multi-threading note: the random number generator used here is not +thread-safe; it is possible that nearly simultaneous calls in +different theads return the same random value. To avoid this, you +have to use a lock around all calls. (I didn't want to slow this +down in the serial case by using a lock here.) +""" class whrandom: - # - # Initialize an instance. - # Without arguments, initialize from current time. - # With arguments (x, y, z), initialize from them. - # def __init__(self, x = 0, y = 0, z = 0): + """Initialize an instance. + Without arguments, initialize from current time. + With arguments (x, y, z), initialize from them.""" self.seed(x, y, z) - # - # Set the seed from (x, y, z). - # These must be integers in the range [0, 256). - # + def seed(self, x = 0, y = 0, z = 0): + """Set the seed from (x, y, z). + These must be integers in the range [0, 256).""" if not type(x) == type(y) == type(z) == type(0): raise TypeError, 'seeds must be integers' if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256): @@ -63,10 +61,9 @@ class whrandom: t, z = divmod(t, 256) # Zero is a poor seed, so substitute 1 self._seed = (x or 1, y or 1, z or 1) - # - # Get the next random number in the range [0.0, 1.0). - # + def random(self): + """Get the next random number in the range [0.0, 1.0).""" # This part is thread-unsafe: # BEGIN CRITICAL SECTION x, y, z = self._seed @@ -79,30 +76,25 @@ class whrandom: # END CRITICAL SECTION # return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0 - # - # Get a random number in the range [a, b). - # + def uniform(self, a, b): + """Get a random number in the range [a, b).""" return a + (b-a) * self.random() - # - # Get a random integer in the range [a, b] including both end points. - # (Deprecated; use randrange below.) - # + def randint(self, a, b): + """Get a random integer in the range [a, b] including both end points. + (Deprecated; use randrange below.)""" return self.randrange(a, b+1) - # - # Choose a random element from a non-empty sequence. - # + def choice(self, seq): + """Choose a random element from a non-empty sequence.""" return seq[int(self.random() * len(seq))] - # - # Choose a random item from range([start,] step[, stop]). - # This fixes the problem with randint() which includes the - # endpoint; in Python this is usually not what you want. - # - def randrange(self, start, stop=None, step=1, - # Do not supply the following arguments - int=int, default=None): + + def randrange(self, start, stop=None, step=1, int=int, default=None): + """Choose a random item from range([start,] step[, stop]). + This fixes the problem with randint() which includes the + endpoint; in Python this is usually not what you want. + Do not supply the 'int' and 'default' arguments.""" # This code is a bit messy to make it fast for the # common case while still doing adequate error checking istart = int(start) @@ -136,7 +128,6 @@ class whrandom: # Initialize from the current time -# _inst = whrandom() seed = _inst.seed random = _inst.random |