----- Original Message ----- > > A while back I noticed that the piglit roundmode-pixelstore and > roundmode-getinteger tests pass on my 64-bit Fedora system but fail > on > a 32-bit Ubuntu system. Both glGetIntegerv() and glPixelStoref() > use > the IROUND() function to convert floats to ints. > > The implementation if IROUND() that uses the x86 fistp instruction is > protected with: > > #if defined(USE_X86_ASM) && defined(__GNUC__) && defined(__i386__) > > but that evaluates to 0 on x86-64 (neither USE_X86_ASM nor __i386__ > are defined) so we use the C fallback: > > #define IROUND(f) ((int) (((f) >= 0.0F) ? ((f) + 0.5F) : ((f) - > 0.5F))) > > The C version of IROUND() does what we want for the piglit tests but > not the x86 version. I think the default x86 rounding mode is > FE_UPWARD so that explains the failures. > > > So I think I'd like to do the following: > > 1. Enable the x86 fistp-based functions in imports.h for x86-64.
It's illegal/inneficient to use x87 on x86-64. We should use the appropriate SSE intrisinsic instead. > 2. Rename IROUND() to IROUND_FAST() and define it as float->int > conversion by whatever method is fastest. > > 3. Define IROUND() as round to nearest int. For the x86 fistp > implementation this would involve setting/restoring the rounding > mode. > > 4. Do an inspection of current IROUND() calls and convert some to > IROUND_FAST() where we can get away with it. It sounds a sensible plan, but I wonder if the multiple iround versions are really worth it: SSE2 is guaranteed in x64, so we could just start requiring SSE2 on x86, and only use the C for other platforms. Jose _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
