I'll get to this asap. Have to install a new "clean" environment aka a new virtual machine. On 18-Aug-16 02:43, Martin Panter wrote: > Martin Panter added the comment: > > Michael, byref() is just a helper for passing an object’s address to a C function. Calling func(byref(b), ...) in Python is equivalent to the C code > > unpack_bitfields(&b, ...) > > I still think the root problem is in unpack_bitfields(). When compiled with XLC, your experiments confirm that it always returns unsigned values, and with GCC, it returns signed values. > > It looks like you can detect XLC with the __IBMC__ and __xlC__ macros (not sure if there is a practical difference). So perhaps we can fix this with > > #ifndef __xlC__ > > ---------- > > _______________________________________ > Python tracker <report@bugs.python.org> > <http://bugs.python.org/issue27643> > _______________________________________