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bpo-44339: Fix math.pow corner case to comply with IEEE 754#26606

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mdickinson merged 9 commits intopython:mainfrom
mdickinson:fix-float-pow-ieee-754-corner-case
Jun 12, 2021
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bpo-44339: Fix math.pow corner case to comply with IEEE 754#26606
mdickinson merged 9 commits intopython:mainfrom
mdickinson:fix-float-pow-ieee-754-corner-case

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@mdickinson mdickinson commented Jun 8, 2021 •
edited by bedevere-bot
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This PR changes the behaviour of math.pow(0.0, -math.inf) and math.pow(-0.0, -math.inf) to return positive infinity instead of raising ValueError. This makes math.pow consistent with the built-in pow (and the ** operator) for this particular special case, and brings the math.pow special-case handling into compliance with IEEE 754.

Before:

Python 3.11.0a0 (heads/main:257e400a19, Jun  8 2021, 18:00:50) [Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.pow(0.0, -math.inf)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: math domain error
>>> math.pow(-0.0, -math.inf)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: math domain error

After:

Python 3.11.0a0 (heads/fix-float-pow-ieee-754-corner-case:1be10ea32f, Jun  8 2021, 17:43:05) [Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.pow(0.0, -math.inf)
inf
>>> math.pow(-0.0, -math.inf)
inf

https://bugs.python.org/issue44339

mdickinson
mdickinson commented Jun 8, 2021
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Comment thread Lib/test/ieee754.txt
corona10
corona10 requested changes Jun 9, 2021
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Comment thread Lib/test/test_math.py
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bedevere-bot commented Jun 9, 2021

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

@mdickinson mdickinson merged commit 4a42ceb into python:main Jun 12, 2021
@mdickinson mdickinson deleted the fix-float-pow-ieee-754-corner-case branch June 12, 2021 09:23
jdevries3133 pushed a commit to jdevries3133/cpython that referenced this pull request Jun 19, 2021
@mdickinson @jdevries3133
bpo-44339: Fix math.pow corner case to comply with IEEE 754 (pythonGH…
869f2fa 
…-26606)

Change the behaviour of `math.pow(0.0, -math.inf)` and `math.pow(-0.0, -math.inf)` to return positive infinity instead of raising `ValueError`. This makes `math.pow` consistent with the built-in `pow` (and the `**` operator) for this particular special case, and brings the `math.pow` special-case handling into compliance with IEEE 754.
@jopemachine jopemachine mentioned this pull request Sep 9, 2022
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@corona10 corona10 corona10 approved these changes

@erlend-aasland erlend-aasland erlend-aasland approved these changes

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@mdickinson @bedevere-bot @corona10 @erlend-aasland @the-knights-who-say-ni