test_cmath fails on ppc with glibc-2.14.90 due to buggy architecture-specific "hypot"

[davidmalcolm]

BPO	13534
Nosy	@mdickinson, @davidmalcolm

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/mdickinson'
closed_at = <Date 2011-12-07.17:27:23.492>
created_at = <Date 2011-12-05.23:24:20.932>
labels = ['tests']
title = 'test_cmath fails on ppc with glibc-2.14.90 due to buggy architecture-specific "hypot"'
updated_at = <Date 2011-12-07.17:27:23.490>
user = 'https://github.com/davidmalcolm'

bugs.python.org fields:

activity = <Date 2011-12-07.17:27:23.490>
actor = 'dmalcolm'
assignee = 'mark.dickinson'
closed = True
closed_date = <Date 2011-12-07.17:27:23.492>
closer = 'dmalcolm'
components = ['Tests']
creation = <Date 2011-12-05.23:24:20.932>
creator = 'dmalcolm'
dependencies = []
files = []
hgrepos = []
issue_num = 13534
keywords = []
message_count = 5.0
messages = ['148893', '148894', '148934', '148936', '148979']
nosy_count = 2.0
nosy_names = ['mark.dickinson', 'dmalcolm']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue13534'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3']

[davidmalcolm]

On ppc64, on this box, with glibc-2.14.90-19.ppc64, test_cmath fails with:

======================================================================
FAIL: test_specific_values (test.test_cmath.CMathTests)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/builddir/build/BUILD/Python-2.7.2/Lib/test/test_cmath.py", line 352,
in test_specific_values
    msg=error_message)
  File "/builddir/build/BUILD/Python-2.7.2/Lib/test/test_cmath.py", line 112,
in rAssertAlmostEqual
    '{!r} and {!r} are not sufficiently close'.format(a, b))
AssertionError: acos0200: acos(complex(1.620686051868302e+308,
1.0308426226285283e+308))
Expected: complex(0.5665082609382622, -710.5420687424156)
Received: complex(0.5665082609382622, -inf)
Received value insufficiently close to expected value.

It turns out (after much debugging) that libm in this version of glibc has an architecture-specific implementation of hypot(3) which returns inf in many of the test cases in tests/cmath_testcases.txt, when the non-architecture-specific implementation returns large finite values.

See downstream bug in Fedora's bug tracker:
https://bugzilla.redhat.com/show_bug.cgi?id=750811
for more details.

Seen with the Python 2.7.2 tarball, but the code doesn't appear to have changed in hg in either the default or the 2.7 branches.

I will also file a bug in glibc's bug tracker about this.

[davidmalcolm]

Reported in glibc's bug tracker as:
http://sourceware.org/bugzilla/show_bug.cgi?id=13472

[davidmalcolm]

The glibc bug has been fixed in that project's git repo:
http://repo.or.cz/w/glibc.git/commit/850fb039cec802072f70ed9763927881bbbf639c

[mdickinson]

Thanks for the report, and all the sleuthing. It's always good to see Python's test suite expose C library (or C compiler) bugs. :-)

I propose closing this as 'won't fix': I certainly wouldn't want to add workarounds in the cmath source (though in theory that would be possible). I don't really think it's worth adding special cases to the test-suite, either. What do you think?

[davidmalcolm]

I agree. I filed this here in case anyone else ran into it, but given that this is really a glibc bug (now fixed), I'm closing this out as "won't fix".