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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() must be called before whrandom.random()
# to seed the generator
# Translated by Guido van Rossum from C source provided by
# Adrian Baddeley.
# The seed
#
_seed = [0, 0, 0]
# Set the seed
#
def seed(x, y, z):
_seed[:] = [x, y, z]
# Return the next random number in the range [0.0 .. 1.0)
#
def random():
from math import floor # floor() function
#
[x, y, z] = _seed
x = 171 * (x % 177) - 2 * (x/177)
y = 172 * (y % 176) - 35 * (y/176)
z = 170 * (z % 178) - 63 * (z/178)
#
if x < 0: x = x + 30269
if y < 0: y = y + 30307
if z < 0: z = z + 30323
#
_seed[:] = [x, y, z]
#
term = float(x)/30269.0 + float(y)/30307.0 + float(z)/30323.0
rand = term - floor(term)
#
if rand >= 1.0: rand = 0.0 # floor() inaccuracy?
#
return rand
# Initialize from the current time
#
def init():
import time
t = time.time()
seed(t%256, t/256%256, t/65536%256)
# Make sure the generator is preset to a nonzero value
#
init()
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