Michael Felt added the comment: On 22-Aug-16 19:43, Eric N. Vander Weele wrote: > Eric N. Vander Weele added the comment: > > I came across this issue while researching where to post my patch (having > come across this while building Python 2.7 & 3.x on AIX via xlc). > >> In general in C, if a bit-field has type “int” without a signed or unsigned >> qualifier, it is up to the implementation which mode is chosen. > Unfortunately, the ISO C standard leaves it up to the compiler to decide > whether to default to 'signed' or 'unsigned' for non-qualified bit-field > declarations. gcc defaults to signed > (https://gcc.gnu.org/onlinedocs/gcc-3.3.6/gcc/Non_002dbugs.html); however, > xlc defaults to unsigned > (https://www.ibm.com/support/knowledgecenter/SSGH2K_13.1.3/com.ibm.xlc1313.aix.doc/compiler_ref/opt_bitfields.html). > >> [...] having bitfields working regardless of the compiler should be >> preferred. > However, ctypes_test assumes an unqualified bit-field will be signed. To > achieve bit-fields working regardless of the compiler, declarations must > explicitly qualifying the sign for bit-fields. This makes the intent of what > is expected explicit and avoids implementation-defined behavior that will > differ from one compiler to the next. > > With patch ctypes_test_sign_bitfields.diff provided, I have verified > ctypes_test passes on Python 2.7, Python 3.4, and Python 3.5 (on AIX & > Solaris). If need be, I'm happy to provide before-&-after output of > ctypes_test with & without the patch applied (or verification from others > would be greatly appreciated). > > ---------- > Added file: http://bugs.python.org/file44189/ctypes_test_sign_bitfields.diff I believe that there is a specific reason that M, N, O, P, Q, R and S are "short". For AIX/xlc at least "signed" is equivalent to "signed int" and not the same size as "unsigned short".
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