CC @picnixz

Sorry Sergey for not replying to your pings. I see them but I'm either doing something else or then I forget about them :(

Merged, thanks.

Thanks @skirpichev for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

Thanks @skirpichev for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

GH-124161 is a backport of this pull request to the 3.13 branch.

GH-124162 is a backport of this pull request to the 3.12 branch.

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows10 3.x has failed when building commit 28aea5d.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/146/builds/9512) and take a look at the build logs.
4. Check if the failure is related to this commit (28aea5d) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/146/builds/9512

Failed tests:

• test_math

Failed subtests:

• testFmod - test.test_math.MathTests.testFmod

Summary of the results of the build (if available):

==

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)

Oh, a test failed on Windows 10:

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)

@skirpichev: Would you mind to have a look at the testFmod() failure?

It's easy: windows=>bugs. Standard says: "The fmod functions compute the floating-point remainder of x/y. [...] if y is nonzero, the result has the same sign as x [...]".

Does it fail on 11? Maybe it's fixed?

Anyway, I'll provide patch to filter out this on Win 10.

Anyway, I'll provide patch to filter out this on Win 10.

Is it possible to fix fmod() bug on Windows?

Unfortunately, I can only guess how it's broken.

Assuming that it's wrong only for signed zero as result, we could replace one with

static double
m_fmod(double x, double y)
{
    double r = fmod(x, y);

    if (r == 0.0 && y != 0.0) {
        r = copysign(r, x);
    }

    return r;
}

Does it fail on 11? Maybe it's fixed?

The test pass on [MSC v.1941 64 bit (AMD64)] (Windows 10 buildbot), but fails on [MSC v.1916 64 bit (AMD64)] (GitHub Actions). It's more a matter of the C Compiler version (MSC).