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[3.13] gh-123836: workaround fmod(x, y) bug on Windows (GH-124171) #124187

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Merged
merged 1 commit into from
Sep 30, 2024
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[3.13] gh-123836: workaround fmod(x, y) bug on Windows (GH-124171) #124187

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2024-09-17-18-06-42.gh-issue-124171.PHCvRJ.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Add workaround for broken :c:func:`!fmod()` implementations on Windows, that
loose zero sign (e.g. ``fmod(-10, 1)`` returns ``0.0``). Patch by Sergey B
Kirpichev.
9 changes: 9 additions & 0 deletions Modules/mathmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2385,6 +2385,15 @@ math_fmod_impl(PyObject *module, double x, double y)
return PyFloat_FromDouble(x);
errno = 0;
r = fmod(x, y);
#ifdef _MSC_VER
/* Windows (e.g. Windows 10 with MSC v.1916) loose sign
for zero result. But C99+ says: "if y is nonzero, the result
has the same sign as x".
*/
if (r == 0.0 && y != 0.0) {
r = copysign(r, x);
}
#endif
if (Py_IS_NAN(r)) {
if (!Py_IS_NAN(x) && !Py_IS_NAN(y))
errno = EDOM;
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