mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-09-17 06:06:25 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 9

Moved Rational._binary_float_to_ratio() to float.as_integer_ratio() because

Browse source 
it's useful outside of rational numbers.

This is my first C code that had to do anything significant. Please be more
careful when looking over it.
This commit is contained in:
Jeffrey Yasskin 2008-01-27 23:08:46 +00:00
parent 56eadd9d0d
commit 3ea7b41b58
3 changed files with 180 additions and 56 deletions
Download patch file Download diff file Expand all files Collapse all files

56
Lib/rational.py
View file

@ -25,60 +25,6 @@ def gcd(a, b):
return a
def _binary_float_to_ratio(x):
"""x -> (top, bot), a pair of ints s.t. x = top/bot.
The conversion is done exactly, without rounding.
bot > 0 guaranteed.
Some form of binary fp is assumed.
Pass NaNs or infinities at your own risk.
>>> _binary_float_to_ratio(10.0)
(10, 1)
>>> _binary_float_to_ratio(0.0)
(0, 1)
>>> _binary_float_to_ratio(-.25)
(-1, 4)
"""
# XXX Move this to floatobject.c with a name like
# float.as_integer_ratio()
if x == 0:
return 0, 1
f, e = math.frexp(x)
signbit = 1
if f < 0:
f = -f
signbit = -1
assert 0.5 <= f < 1.0
# x = signbit * f * 2**e exactly
# Suck up CHUNK bits at a time; 28 is enough so that we suck
# up all bits in 2 iterations for all known binary double-
# precision formats, and small enough to fit in an int.
CHUNK = 28
top = 0
# invariant: x = signbit * (top + f) * 2**e exactly
while f:
f = math.ldexp(f, CHUNK)
digit = trunc(f)
assert digit >> CHUNK == 0
top = (top << CHUNK) | digit
f = f - digit
assert 0.0 <= f < 1.0
e = e - CHUNK
assert top
# Add in the sign bit.
top = signbit * top
# now x = top * 2**e exactly; fold in 2**e
if e>0:
return (top * 2**e, 1)
else:
return (top, 2 ** -e)
_RATIONAL_FORMAT = re.compile(
r'^\s*(?P<sign>[-+]?)(?P<num>\d+)'
r'(?:/(?P<denom>\d+)|\.(?P<decimal>\d+))?\s*$')
@ -163,7 +109,7 @@ class Rational(RationalAbc):
(cls.__name__, f, type(f).__name__))
if math.isnan(f) or math.isinf(f):
raise TypeError("Cannot convert %r to %s." % (f, cls.__name__))
return cls(*_binary_float_to_ratio(f))
return cls(*f.as_integer_ratio())
@classmethod
def from_decimal(cls, dec):