| # 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, *xyz): |
| if not xyz: |
| # Initialize from current time |
| import time |
| t = int(time.time()) |
| t, x = divmod(t, 256) |
| t, y = divmod(t, 256) |
| t, z = divmod(t, 256) |
| else: |
| # Initialize from arguments (x, y, z) |
| x, y, z = xyz |
| self.seed(x, y, z) |
| # |
| # Set the seed from (x, y, z). |
| # These must be integers in the range [0, 256). |
| # |
| def seed(self, *xyz): |
| if type(xyz) <> type(()) or len(xyz) <> 3: |
| raise TypeError, '3 seeds required' |
| x, y, z = xyz |
| 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 = xyz |
| # |
| # 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 |