[New-bugs-announce] [issue18739] math.log of a long returns a different value of math.log of an int

[Gregory P. Smith]

New submission from Gregory P. Smith:

This is a very odd inconsistency in math.log behavior.  That said, it is probably only a single bit imprecision at the end of the float result.  Still, 10 == 10L so I'd expect math.log of both to give the same result.

oss/cpython/2.7:LOAS$ ./python
Python 2.7.5+ (2.7:395ac61ebe1a, Aug 14 2013, 07:11:35) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.log(10) - math.log(10L)
4.440892098500626e-16
>>> math.log(10)
2.302585092994046
>>> math.log(10L)
2.3025850929940455
>>> 

In Python 3.3 things seem fine and match the int behavior from 2.7 above despite the internal number implementation being a PyLong in 3.x:

>>> math.log(10)
2.302585092994046

----------
messages: 195175
nosy: gregory.p.smith
priority: normal
severity: normal
status: open
title: math.log of a long returns a different value of math.log of an int
versions: Python 2.7

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18739>
_______________________________________