double_abs test failures in 3.0.11

[apteryks]

Bug report

Bug description:

Hi,

Running the test suite of Cython 3.0.11 with GNU Guix, I see the following doctests failures:

======================================================================
FAIL: double_abs (complex_numbers_cpp)
Doctest: complex_numbers_cpp.double_abs
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/gnu/store/lp8ch4rn10whzyajnzv216d2a2v163c7-python-3.10.7/lib/python3.10/doctest.py", line 2221, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for complex_numbers_cpp.double_abs
  File "/tmp/guix-build-python-cython-3.0.11.drv-0/cython-3.0.11/TEST_TMP/14/run/cpp/complex_numbers_cpp/complex_numbers_cpp.cpython-310-x86_64-linux-gnu.so", line unknown line number, in double_abs

----------------------------------------------------------------------
File "/tmp/guix-build-python-cython-3.0.11.drv-0/cython-3.0.11/TEST_TMP/14/run/cpp/complex_numbers_cpp/complex_numbers_cpp.cpython-310-x86_64-linux-gnu.so", line ?, in complex_numbers_cpp.double_abs
Failed example:
    double_abs(2 + 5j) == math.sqrt(29)
Expected:
    True
Got:
    False


======================================================================
FAIL: double_abs (complex_numbers_cpp)
Doctest: complex_numbers_cpp.double_abs
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/gnu/store/lp8ch4rn10whzyajnzv216d2a2v163c7-python-3.10.7/lib/python3.10/doctest.py", line 2221, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for complex_numbers_cpp.double_abs
  File "/tmp/guix-build-python-cython-3.0.11.drv-0/cython-3.0.11/TEST_TMP/14/run/cpp/complex_numbers_cpp_directives_cpp_locals_True/complex_numbers_cpp.cpython-310-x86_64-linux-gnu.so", line unknown line number, in double_abs

----------------------------------------------------------------------
File "/tmp/guix-build-python-cython-3.0.11.drv-0/cython-3.0.11/TEST_TMP/14/run/cpp/complex_numbers_cpp_directives_cpp_locals_True/complex_numbers_cpp.cpython-310-x86_64-linux-gnu.so", line ?, in complex_numbers_cpp.double_abs
Failed example:
    double_abs(2 + 5j) == math.sqrt(29)
Expected:
    True
Got:
    False


----------------------------------------------------------------------
Ran 579 tests in 86.348s

FAILED (failures=2)

The only direct dependencies added to the build environment are:
libxcrypt@4.4.36 python@3.10.7. GCC is at version 11.4.0.

CPython versions tested on:

3.10

Operating systems tested on:

Linux

[picnixz]

Isn't it a Cython-only issue? This should be reported to their repository instead I think.

[skirpichev]

Yes, that's definitely not a CPython issue. Please report it here: https://github.com/cython/cython/issues

I would guess it might also depend to how you built Cython. Perhaps, in your case double_abs() is using libm's complex functions, which may be less accurate or just produce a slightly different answer than math.sqrt(29).

Using == to compare computed floating-point values usually is not safe. It's OK only if both lhs and rhs are computed by exactly same algorithm.

[apteryks]

And I thought I was reporting this to Cython! Sorry for my bout of dyslexia.