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HardwareRandom: Go back to multiplying by 2**-BPF instead of using

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ldexp.  Both methods are exact, and return the same results.  Turns out
multiplication is a few (but just a few) percent faster on my box.
They're both significantly faster than using struct with a Q format
to convert bytes to a 64-bit long (struct.unpack() appears to lose due
to the tuple creation/teardown overhead), and calling _hexlify is
significantly faster than doing bytes.encode('hex').  So we appear to
have hit a local minimum (wrt speed) here.
This commit is contained in:
Tim Peters 2004-08-31 02:19:55 +00:00
parent 3fa19d7ff8
commit 7c2a85b2d4
1 changed files with 3 additions and 2 deletions
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5
Lib/random.py
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@ -43,7 +43,7 @@ from warnings import warn as _warn
from types import MethodType as _MethodType, BuiltinMethodType as _BuiltinMethodType from types import MethodType as _MethodType, BuiltinMethodType as _BuiltinMethodType
from math import log as _log, exp as _exp, pi as _pi, e as _e from math import log as _log, exp as _exp, pi as _pi, e as _e
from math import sqrt as _sqrt, acos as _acos, cos as _cos, sin as _sin from math import sqrt as _sqrt, acos as _acos, cos as _cos, sin as _sin
from math import floor as _floor, ldexp as _ldexp from math import floor as _floor
__all__ = ["Random","seed","random","uniform","randint","choice","sample", __all__ = ["Random","seed","random","uniform","randint","choice","sample",
"randrange","shuffle","normalvariate","lognormvariate", "randrange","shuffle","normalvariate","lognormvariate",
@ -57,6 +57,7 @@ TWOPI = 2.0*_pi
LOG4 = _log(4.0) LOG4 = _log(4.0)
SG_MAGICCONST = 1.0 + _log(4.5) SG_MAGICCONST = 1.0 + _log(4.5)
BPF = 53 # Number of bits in a float BPF = 53 # Number of bits in a float
RECIP_BPF = 2**-BPF
try: try:
from os import urandom as _urandom from os import urandom as _urandom
@ -759,7 +760,7 @@ class HardwareRandom(Random):
"""Get the next random number in the range [0.0, 1.0).""" """Get the next random number in the range [0.0, 1.0)."""
if _urandom is None: if _urandom is None:
raise NotImplementedError('Cannot find hardware entropy source') raise NotImplementedError('Cannot find hardware entropy source')
return _ldexp(long(_hexlify(_urandom(7)), 16) >> 3, -BPF) return (long(_hexlify(_urandom(7)), 16) >> 3) * RECIP_BPF
def getrandbits(self, k): def getrandbits(self, k):
"""getrandbits(k) -> x. Generates a long int with k random bits.""" """getrandbits(k) -> x. Generates a long int with k random bits."""