diff options
Diffstat (limited to 'Lib/random.py')
| -rw-r--r-- | Lib/random.py | 70 |
1 files changed, 62 insertions, 8 deletions
diff --git a/Lib/random.py b/Lib/random.py index 7ec6583..06990d2 100644 --- a/Lib/random.py +++ b/Lib/random.py @@ -49,7 +49,8 @@ __all__ = ["Random","seed","random","uniform","randint","choice","sample", "randrange","shuffle","normalvariate","lognormvariate", "expovariate","vonmisesvariate","gammavariate", "gauss","betavariate","paretovariate","weibullvariate", - "getstate","setstate","jumpahead", "WichmannHill", "getrandbits"] + "getstate","setstate","jumpahead", "WichmannHill", "getrandbits", + "HardwareRandom"] NV_MAGICCONST = 4 * _exp(-0.5)/_sqrt(2.0) TWOPI = 2.0*_pi @@ -57,6 +58,15 @@ LOG4 = _log(4.0) SG_MAGICCONST = 1.0 + _log(4.5) BPF = 53 # Number of bits in a float +try: + from os import urandom as _urandom + from binascii import hexlify as _hexlify +except ImportError: + _urandom = None +else: + _tofloat = 2.0 ** (-7*8) # converts 7 byte integers to floats + + # Translated by Guido van Rossum from C source provided by # Adrian Baddeley. Adapted by Raymond Hettinger for use with # the Mersenne Twister core generator. @@ -94,14 +104,19 @@ class Random(_random.Random): def seed(self, a=None): """Initialize internal state from hashable object. - None or no argument seeds from current time. + None or no argument seeds from current time or from a hardware + randomness source if available. If a is not None or an int or long, hash(a) is used instead. """ if a is None: - import time - a = long(time.time() * 256) # use fractional seconds + if _urandom is None: + import time + a = long(time.time() * 256) # use fractional seconds + else: + a = long(_hexlify(_urandom(16)), 16) + super(Random, self).seed(a) self.gauss_next = None @@ -593,7 +608,8 @@ class WichmannHill(Random): def seed(self, a=None): """Initialize internal state from hashable object. - None or no argument seeds from current time. + None or no argument seeds from current time or from a hardware + randomness source if available. If a is not None or an int or long, hash(a) is used instead. @@ -604,9 +620,11 @@ class WichmannHill(Random): """ if a is None: - # Initialize from current time - import time - a = long(time.time() * 256) + if _urandom is None: + import time + a = long(time.time() * 256) # use fractional seconds + else: + a = long(_hexlify(_urandom(16)), 16) if not isinstance(a, (int, long)): a = hash(a) @@ -731,6 +749,42 @@ class WichmannHill(Random): z = (z + a) % 256 or 1 self.__whseed(x, y, z) +## -------------------- Hardware Random Source ------------------- + +class HardwareRandom(Random): + """Alternate random number generator using hardware sources. + + Not available on all systems (see os.urandom() for details). + """ + + def random(self): + """Get the next random number in the range [0.0, 1.0).""" + if _urandom is None: + raise NotImplementedError('Cannot find hardware entropy source') + return long(_hexlify(_urandom(7)), 16) * _tofloat + + def getrandbits(self, k): + """getrandbits(k) -> x. Generates a long int with k random bits.""" + if _urandom is None: + raise NotImplementedError('Cannot find hardware entropy source') + if k <= 0: + raise ValueError('number of bits must be greater than zero') + if k != int(k): + raise TypeError('number of bits should be an integer') + bytes = (k + 7) // 8 # bits / 8 and rounded up + x = long(_hexlify(_urandom(bytes)), 16) + return x >> (bytes * 8 - k) # trim excess bits + + def _stub(self, *args, **kwds): + "Stub method. Not used for a hardware random number generator." + return None + seed = jumpahead = _stub + + def _notimplemented(self, *args, **kwds): + "Method should not be called for a hardware random number generator." + raise NotImplementedError('Hardware entropy source does not have state.') + getstate = setstate = _notimplemented + ## -------------------- test program -------------------- def _test_generator(n, func, args): |