[issue16733] Solaris ctypes_test failures

[Greg Onufer]

Greg Onufer <gonufer at jazzhaiku.com> added the comment:

The bitfields failures are due to Python not implementing bitfields the same as the compiler.

https://docs.oracle.com/cd/E77782_01/html/E77792/gqexw.html

"Signed and Unsigned int Bit-fields
Bit-fields which are declared as int (not signed int or unsigned int) can be implemented by the compiler using either signed or unsigned types. This makes a difference when extracting a value and deciding whether to sign extend it.

The Oracle Developer Studio compiler uses unsigned types for int bit-fields and the gcc compiler uses signed types. Use the gcc –funsigned-bitfields flag to control this behavior.

For more information, see the sixth list item at https://gcc.gnu.org/onlinedocs/gcc-3.3.6/gcc/Non_002dbugs.html."

When the test compares the ctypes extraction of the bitfield (signed) and the compiler-native extraction of the bitfield (unsigned), they miscompare if the high-bit of the field is set.

If Python wants bitfields extracted from signed integral types to be signed, the C code in the test case needs to account for the compiler implementation defined behavior and sign extend the bitfield before returning it.

See patch in attachment.  The bitfield tests pass with those changes.

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keywords: +patch
nosy: +gco
Added file: https://bugs.python.org/file47580/0001-Fix-ctypes-bitfield-test-code-to-account-for-compile.patch

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