diff options
Diffstat (limited to 'Lib/random.py')
| -rw-r--r-- | Lib/random.py | 42 |
1 files changed, 38 insertions, 4 deletions
diff --git a/Lib/random.py b/Lib/random.py index a818f73..1b91886 100644 --- a/Lib/random.py +++ b/Lib/random.py @@ -72,8 +72,8 @@ class Random: self.gauss_next = None # Specific to Wichmann-Hill generator. Subclasses wishing to use a - # different core generator should override seed(), random(), getstate() - # and setstate(). + # different core generator should override the seed(), random(), + # getstate(), setstate(), and jumpahead() methods. def __whseed(self, x=0, y=0, z=0): """Set the Wichmann-Hill seed from (x, y, z). @@ -104,6 +104,7 @@ class Random: if a is None: self.__whseed() + return a = hash(a) a, x = divmod(a, 256) a, y = divmod(a, 256) @@ -115,11 +116,10 @@ class Random: def getstate(self): """Return internal state; can be passed to setstate() later.""" - return self.VERSION, self._seed, self.gauss_next def __getstate__(self): # for pickle - self.getstate() + return self.getstate() def setstate(self, state): """Restore internal state from object returned by getstate().""" @@ -134,6 +134,28 @@ class Random: def __setstate__(self, state): # for pickle self.setstate(state) + def jumpahead(self, n): + """Act as if n calls to random() were made, but quickly. + + n is an int, greater than or equal to 0. + + Example use: If you have 2 threads and know that each will + consume no more than a million random numbers, create two Random + objects r1 and r2, then do + r2.setstate(r1.getstate()) + r2.jumpahead(1000000) + Then r1 and r2 will use guaranteed-disjoint segments of the full + period. + """ + + if not n >= 0: + raise ValueError("n must be >= 0") + x, y, z = self._seed + x = int(x * pow(171, n, 30269)) % 30269 + y = int(y * pow(172, n, 30307)) % 30307 + z = int(z * pow(170, n, 30323)) % 30323 + self._seed = x, y, z + def random(self): """Get the next random number in the range [0.0, 1.0).""" @@ -471,6 +493,17 @@ def _test_generator(n, funccall): print 'avg %g, stddev %g, min %g, max %g' % \ (avg, stddev, smallest, largest) + s = getstate() + N = 1019 + jumpahead(N) + r1 = random() + setstate(s) + for i in range(N): # now do it the slow way + random() + r2 = random() + if r1 != r2: + raise ValueError("jumpahead test failed " + `(N, r1, r2)`) + def _test(N=200): print 'TWOPI =', TWOPI print 'LOG4 =', LOG4 @@ -515,6 +548,7 @@ paretovariate = _inst.paretovariate weibullvariate = _inst.weibullvariate getstate = _inst.getstate setstate = _inst.setstate +jumpahead = _inst.jumpahead if __name__ == '__main__': _test() |