https://github.com/python/cpython/commit/8fffbb098259ed413d75dbc2e6d3e540425bd9b9 commit: 8fffbb098259ed413d75dbc2e6d3e540425bd9b9 branch: 3.12 author: Miss Islington (bot) <[email protected]> committer: gpshead <[email protected]> date: 2024-12-02T19:47:42Z summary:
[3.12] gh-113841: fix possible undefined division by 0 in _Py_c_pow() (GH-127211) (GH-127216) (GH-127530) [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 f7bb658124aba74be4c13f498bf46cfded710ef9) (cherry picked from commit f41d8d89e79d634895868656f50a0e16e339f9d6) Co-authored-by: Sergey B Kirpichev <[email protected]> files: A Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst M Lib/test/test_complex.py M Objects/complexobject.c diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py index 4272c2afcdc274..f12e1c8bd7094a 100644 --- a/Lib/test/test_complex.py +++ b/Lib/test/test_complex.py @@ -300,6 +300,11 @@ def test_pow(self): 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. diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst new file mode 100644 index 00000000000000..2b07fdfcc6b527 --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-11-24-07-01-28.gh-issue-113841.WFg-Bu.rst @@ -0,0 +1,2 @@ +Fix possible undefined behavior division by zero in :class:`complex`'s +:c:func:`_Py_c_pow`. diff --git a/Objects/complexobject.c b/Objects/complexobject.c index 7f7e7e6b08cdca..eff173802984b6 100644 --- a/Objects/complexobject.c +++ b/Objects/complexobject.c @@ -146,7 +146,7 @@ _Py_c_pow(Py_complex a, Py_complex b) at = atan2(a.imag, a.real); phase = at*b.real; if (b.imag != 0.0) { - len /= exp(at*b.imag); + len *= exp(-at*b.imag); phase += b.imag*log(vabs); } r.real = len*cos(phase); _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-checkins.python.org/ Member address: [email protected]
