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# 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.
class whrandom:
#
# Initialize an instance.
# Without arguments, initialize from current time.
# With arguments (x, y, z), initialize from them.
#
def __init__(self, x = None, y = None, z = None):
if x is None:
# Initialize from current time
import time
t = int(time.time() % 0x80000000)
t, x = divmod(t, 256)
t, y = divmod(t, 256)
t, z = divmod(t, 256)
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, y, z):
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)'
self._seed = (x, y, z)
#
# Get the next random number in the range [0.0, 1.0).
#
def random(self):
x, y, z = self._seed
#
x1, x2 = divmod(x, 177)
y1, y2 = divmod(y, 176)
z1, z2 = divmod(z, 178)
#
x = (171 * x2 - 2 * x1) % 30269
y = (172 * y2 - 35 * y1) % 30307
z = (170 * z2 - 63 * z1) % 30323
#
self._seed = x, y, z
#
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
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