svn-gvsig-desktop / tags / v1_0_2_Build_907 / extensions / extScripting / scripts / jython / Lib / whrandom.py @ 11015
History | View | Annotate | Download (4.67 KB)
1 |
"""Wichman-Hill random number generator.
|
---|---|
2 |
|
3 |
Wichmann, B. A. & Hill, I. D. (1982)
|
4 |
Algorithm AS 183:
|
5 |
An efficient and portable pseudo-random number generator
|
6 |
Applied Statistics 31 (1982) 188-190
|
7 |
|
8 |
see also:
|
9 |
Correction to Algorithm AS 183
|
10 |
Applied Statistics 33 (1984) 123
|
11 |
|
12 |
McLeod, A. I. (1985)
|
13 |
A remark on Algorithm AS 183
|
14 |
Applied Statistics 34 (1985),198-200
|
15 |
|
16 |
|
17 |
USE:
|
18 |
whrandom.random() yields double precision random numbers
|
19 |
uniformly distributed between 0 and 1.
|
20 |
|
21 |
whrandom.seed(x, y, z) must be called before whrandom.random()
|
22 |
to seed the generator
|
23 |
|
24 |
There is also an interface to create multiple independent
|
25 |
random generators, and to choose from other ranges.
|
26 |
|
27 |
|
28 |
|
29 |
Multi-threading note: the random number generator used here is not
|
30 |
thread-safe; it is possible that nearly simultaneous calls in
|
31 |
different theads return the same random value. To avoid this, you
|
32 |
have to use a lock around all calls. (I didn't want to slow this
|
33 |
down in the serial case by using a lock here.)
|
34 |
"""
|
35 |
|
36 |
# Translated by Guido van Rossum from C source provided by
|
37 |
# Adrian Baddeley.
|
38 |
|
39 |
|
40 |
class whrandom: |
41 |
def __init__(self, x = 0, y = 0, z = 0): |
42 |
"""Initialize an instance.
|
43 |
Without arguments, initialize from current time.
|
44 |
With arguments (x, y, z), initialize from them."""
|
45 |
self.seed(x, y, z)
|
46 |
|
47 |
def seed(self, x = 0, y = 0, z = 0): |
48 |
"""Set the seed from (x, y, z).
|
49 |
These must be integers in the range [0, 256)."""
|
50 |
if not type(x) == type(y) == type(z) == type(0): |
51 |
raise TypeError, 'seeds must be integers' |
52 |
if not (0 <= x < 256 and 0 <= y < 256 and 0 <= z < 256): |
53 |
raise ValueError, 'seeds must be in range(0, 256)' |
54 |
if 0 == x == y == z: |
55 |
# Initialize from current time
|
56 |
import time |
57 |
t = long(time.time() * 256) |
58 |
t = int((t&0xffffff) ^ (t>>24)) |
59 |
t, x = divmod(t, 256) |
60 |
t, y = divmod(t, 256) |
61 |
t, z = divmod(t, 256) |
62 |
# Zero is a poor seed, so substitute 1
|
63 |
self._seed = (x or 1, y or 1, z or 1) |
64 |
|
65 |
def random(self): |
66 |
"""Get the next random number in the range [0.0, 1.0)."""
|
67 |
# This part is thread-unsafe:
|
68 |
# BEGIN CRITICAL SECTION
|
69 |
x, y, z = self._seed
|
70 |
#
|
71 |
x = (171 * x) % 30269 |
72 |
y = (172 * y) % 30307 |
73 |
z = (170 * z) % 30323 |
74 |
#
|
75 |
self._seed = x, y, z
|
76 |
# END CRITICAL SECTION
|
77 |
#
|
78 |
return (x/30269.0 + y/30307.0 + z/30323.0) % 1.0 |
79 |
|
80 |
def uniform(self, a, b): |
81 |
"""Get a random number in the range [a, b)."""
|
82 |
return a + (b-a) * self.random() |
83 |
|
84 |
def randint(self, a, b): |
85 |
"""Get a random integer in the range [a, b] including
|
86 |
both end points.
|
87 |
|
88 |
(Deprecated; use randrange below.)"""
|
89 |
return self.randrange(a, b+1) |
90 |
|
91 |
def choice(self, seq): |
92 |
"""Choose a random element from a non-empty sequence."""
|
93 |
return seq[int(self.random() * len(seq))] |
94 |
|
95 |
def randrange(self, start, stop=None, step=1, int=int, default=None): |
96 |
"""Choose a random item from range(start, stop[, step]).
|
97 |
|
98 |
This fixes the problem with randint() which includes the
|
99 |
endpoint; in Python this is usually not what you want.
|
100 |
Do not supply the 'int' and 'default' arguments."""
|
101 |
# This code is a bit messy to make it fast for the
|
102 |
# common case while still doing adequate error checking
|
103 |
istart = int(start)
|
104 |
if istart != start:
|
105 |
raise ValueError, "non-integer arg 1 for randrange()" |
106 |
if stop is default: |
107 |
if istart > 0: |
108 |
return int(self.random() * istart) |
109 |
raise ValueError, "empty range for randrange()" |
110 |
istop = int(stop)
|
111 |
if istop != stop:
|
112 |
raise ValueError, "non-integer stop for randrange()" |
113 |
if step == 1: |
114 |
if istart < istop:
|
115 |
return istart + int(self.random() * |
116 |
(istop - istart)) |
117 |
raise ValueError, "empty range for randrange()" |
118 |
istep = int(step)
|
119 |
if istep != step:
|
120 |
raise ValueError, "non-integer step for randrange()" |
121 |
if istep > 0: |
122 |
n = (istop - istart + istep - 1) / istep
|
123 |
elif istep < 0: |
124 |
n = (istop - istart + istep + 1) / istep
|
125 |
else:
|
126 |
raise ValueError, "zero step for randrange()" |
127 |
|
128 |
if n <= 0: |
129 |
raise ValueError, "empty range for randrange()" |
130 |
return istart + istep*int(self.random() * n) |
131 |
|
132 |
|
133 |
# Initialize from the current time
|
134 |
_inst = whrandom() |
135 |
seed = _inst.seed |
136 |
random = _inst.random |
137 |
uniform = _inst.uniform |
138 |
randint = _inst.randint |
139 |
choice = _inst.choice |
140 |
randrange = _inst.randrange |