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gh-123836: workaround fmod(x, y) bug on Windows (#124171)

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Buildbot failure on Windows 10 with MSC v.1916 64 bit (AMD64):
FAIL: testFmod (test.test_math.MathTests.testFmod)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\buildarea\3.x.bolen-windows10\build\Lib\test\test_math.py", line 605, in testFmod
    self.ftest('fmod(-10, 1)', math.fmod(-10, 1), -0.0)
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\buildarea\3.x.bolen-windows10\build\Lib\test\test_math.py", line 258, in ftest
    self.fail("{}: {}".format(name, failure))
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: fmod(-10, 1): expected -0.0, got 0.0 (zero has wrong sign)

Here Windows loose sign of the result; if y is nonzero, the result
should have the same sign as x.

This amends commit 28aea5d07d.
This commit is contained in:
Sergey B Kirpichev 2024-09-17 20:16:15 +03:00 • committed by GitHub
parent f15fff3f13
commit f4dd440210
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3
Misc/NEWS.d/next/Library/2024-09-17-18-06-42.gh-issue-124171.PHCvRJ.rst Normal file
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@ -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
Modules/mathmodule.c
View file

@ -2348,6 +2348,15 @@ math_fmod_impl(PyObject *module, double x, double y)
return PyFloat_FromDouble(x); return PyFloat_FromDouble(x);
errno = 0; errno = 0;
r = fmod(x, y); 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 (isnan(r)) { if (isnan(r)) {
if (!isnan(x) && !isnan(y)) if (!isnan(x) && !isnan(y))
errno = EDOM; errno = EDOM;