mirror of https://github.com/python/cpython
107 lines
2.8 KiB
Python
107 lines
2.8 KiB
Python
# 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.)
|
|
|
|
|
|
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):
|
|
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):
|
|
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):
|
|
raise ValueError, 'seeds must be in range(0, 256)'
|
|
if 0 == x == y == z:
|
|
# Initialize from current time
|
|
import time
|
|
t = long(time.time() * 256)
|
|
t = int((t&0xffffff) ^ (t>>24))
|
|
t, x = divmod(t, 256)
|
|
t, y = divmod(t, 256)
|
|
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):
|
|
# This part is thread-unsafe:
|
|
# BEGIN CRITICAL SECTION
|
|
x, y, z = self._seed
|
|
#
|
|
x = (171 * x) % 30269
|
|
y = (172 * y) % 30307
|
|
z = (170 * z) % 30323
|
|
#
|
|
self._seed = x, y, z
|
|
# 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):
|
|
return a + (b-a) * self.random()
|
|
#
|
|
# Get a random integer in the range [a, b] including both end points.
|
|
#
|
|
def randint(self, a, b):
|
|
return a + int(self.random() * (b+1-a))
|
|
#
|
|
# Choose a random element from a non-empty sequence.
|
|
#
|
|
def choice(self, seq):
|
|
return seq[int(self.random() * len(seq))]
|
|
|
|
|
|
# Initialize from the current time
|
|
#
|
|
_inst = whrandom()
|
|
seed = _inst.seed
|
|
random = _inst.random
|
|
uniform = _inst.uniform
|
|
randint = _inst.randint
|
|
choice = _inst.choice
|