mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-08-09 19:38:42 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 10

[3.12] gh-113841: fix possible undefined division by 0 in _Py_c_pow() (GH-127211) (GH-127216) (GH-127530)

Browse source 
[3.13] gh-113841: fix possible undefined division by 0 in _Py_c_pow() (GH-127211) (GH-127216)

Note, that transformed expression is not an equivalent for original one (1/exp(-x) != exp(x) in general for floating-point numbers). Though, the difference seems to be ~1ULP for good libm implementations.

It's more interesting why division was used from beginning. Closest algorithm I've found (no error checks, of course;)) - it's Algorithm 190 from ACM: https://dl.acm.org/doi/10.1145/366663.366679. It uses subtraction in the exponent.

(cherry picked from commit f7bb658124)

(cherry picked from commit f41d8d89e7)

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>
This commit is contained in:
Miss Islington (bot) 2024-12-02 20:47:42 +01:00 • committed by GitHub
parent 34fe4af8a2
commit 8fffbb0982
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
3 changed files with 8 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

5
Lib/test/test_complex.py
View file

@ -300,6 +300,11 @@ class ComplexTest(ComplexesAreIdenticalMixin, unittest.TestCase):
except OverflowError:
pass
# gh-113841: possible undefined division by 0 in _Py_c_pow()
x, y = 9j, 33j**3
with self.assertRaises(OverflowError):
x**y
def test_pow_with_small_integer_exponents(self):
# Check that small integer exponents are handled identically
# regardless of their type.