[New-bugs-announce] [issue42323] [AIX] test_math: test_nextafter(float('nan'), 1.0) does not return a NaN on AIX

[STINNER Victor]

New submission from STINNER Victor <vstinner at python.org>:

https://buildbot.python.org/all/#/builders/302/builds/338

FAIL: test_nextafter (test.test_math.MathTests)
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Traceback (most recent call last):
  File "/home/aixtools/buildarea/3.9.aixtools-aix-power6/build/Lib/test/test_math.py", line 1968, in test_nextafter
    self.assertIsNaN(math.nextafter(NAN, 1.0))
  File "/home/aixtools/buildarea/3.9.aixtools-aix-power6/build/Lib/test/test_math.py", line 2015, in assertIsNaN
    self.fail("Expected a NaN, got {!r}.".format(value))
AssertionError: Expected a NaN, got 1.0.

The test:

        # NaN
        self.assertIsNaN(math.nextafter(NAN, 1.0))   # <=== HERE
        self.assertIsNaN(math.nextafter(1.0, NAN))
        self.assertIsNaN(math.nextafter(NAN, NAN))

The Linux manual page says: "If x or y is a NaN, a NaN is returned."
https://man7.org/linux/man-pages/man3/nextafter.3.html

But it seems like the AIX libc doesn't implement this rule. Should we implement this rule in Python on AIX?

The strange thing is that it worked previously. test.python of build 338:

platform.platform: AIX-2-00F9C1964C00-powerpc-32bit
sysconfig[HOST_GNU_TYPE]: powerpc-ibm-aix7.2.4.0
platform.architecture: 32bit

The latest green build is built 347. test.pythoninfo of build 347:

platform.architecture: 32bit
platform.platform: AIX-2-00F9C1964C00-powerpc-32bit
sysconfig[HOST_GNU_TYPE]: powerpc-ibm-aix7.2.0.0

Was the machine updated two days ago (2020-11-09), between build 338 and build 347?

----------
components: Tests
messages: 380751
nosy: lemburg, mark.dickinson, rhettinger, stutzbach, vstinner
priority: normal
severity: normal
status: open
title: [AIX] test_math: test_nextafter(float('nan'), 1.0) does not return a NaN on AIX
versions: Python 3.10

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42323>
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