mirror of
https://github.com/python/cpython.git
synced 2024-12-01 03:01:36 +01:00
75 lines
1.4 KiB
Python
75 lines
1.4 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() 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()
|