mirror of
https://github.com/python/cpython.git
synced 2025-10-31 05:31:20 +00:00
144 lines
4.8 KiB
Python
144 lines
4.8 KiB
Python
"""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.
|
|
|
|
|
|
|
|
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.)
|
|
"""
|
|
|
|
import warnings
|
|
warnings.warn("the whrandom module is deprecated; please use the random module",
|
|
DeprecationWarning)
|
|
|
|
# Translated by Guido van Rossum from C source provided by
|
|
# Adrian Baddeley.
|
|
|
|
|
|
class whrandom:
|
|
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)
|
|
|
|
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):
|
|
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)
|
|
|
|
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
|
|
#
|
|
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
|
|
|
|
def uniform(self, a, b):
|
|
"""Get a random number in the range [a, b)."""
|
|
return a + (b-a) * self.random()
|
|
|
|
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)
|
|
|
|
def choice(self, seq):
|
|
"""Choose a random element from a non-empty sequence."""
|
|
return seq[int(self.random() * len(seq))]
|
|
|
|
def randrange(self, start, stop=None, step=1, int=int, default=None):
|
|
"""Choose a random item from range(start, stop[, step]).
|
|
|
|
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)
|
|
if istart != start:
|
|
raise ValueError, "non-integer arg 1 for randrange()"
|
|
if stop is default:
|
|
if istart > 0:
|
|
return int(self.random() * istart)
|
|
raise ValueError, "empty range for randrange()"
|
|
istop = int(stop)
|
|
if istop != stop:
|
|
raise ValueError, "non-integer stop for randrange()"
|
|
if step == 1:
|
|
if istart < istop:
|
|
return istart + int(self.random() *
|
|
(istop - istart))
|
|
raise ValueError, "empty range for randrange()"
|
|
istep = int(step)
|
|
if istep != step:
|
|
raise ValueError, "non-integer step for randrange()"
|
|
if istep > 0:
|
|
n = (istop - istart + istep - 1) / istep
|
|
elif istep < 0:
|
|
n = (istop - istart + istep + 1) / istep
|
|
else:
|
|
raise ValueError, "zero step for randrange()"
|
|
|
|
if n <= 0:
|
|
raise ValueError, "empty range for randrange()"
|
|
return istart + istep*int(self.random() * n)
|
|
|
|
|
|
# Initialize from the current time
|
|
_inst = whrandom()
|
|
seed = _inst.seed
|
|
random = _inst.random
|
|
uniform = _inst.uniform
|
|
randint = _inst.randint
|
|
choice = _inst.choice
|
|
randrange = _inst.randrange
|