http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51446
--- Comment #13 from lucier at math dot purdue.edu 2011-12-08 20:54:18 UTC --- On Thu, 2011-12-08 at 20:37 +0000, joseph at codesourcery dot com wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51446 > > --- Comment #12 from joseph at codesourcery dot com <joseph at codesourcery > dot com> 2011-12-08 20:37:11 UTC --- > I think the soft-fp code tries to generate particular target-specific NaNs > because it's also used in the Linux kernel emulation of floating-point > instructions - which is a use case where doing the same as particular > hardware is desirable. Indeed, I couldn't find a place in the gcc sources where this macro was used: heine:~/programs/gcc/mainline> grep -R _FP_NANSIGN_Q * | grep -v svn libgcc/config/ia64/sfp-machine.h:#define _FP_NANSIGN_Q 1 libgcc/config/score/sfp-machine.h:#define _FP_NANSIGN_Q 0 libgcc/config/rs6000/sfp-machine.h:#define _FP_NANSIGN_Q 0 libgcc/config/i386/32/sfp-machine.h:#define _FP_NANSIGN_Q 1 libgcc/config/i386/64/sfp-machine.h:#define _FP_NANSIGN_Q 1 libgcc/config/c6x/sfp-machine.h:#define _FP_NANSIGN_Q 0 libgcc/config/moxie/sfp-machine.h:#define _FP_NANSIGN_Q 0 libgcc/config/lm32/sfp-machine.h:#define _FP_NANSIGN_Q 0 libgcc/config/arm/sfp-machine.h:#define _FP_NANSIGN_Q 0 > At the level of GCC compiling C code, the compiler provides the language > semantics. It doesn't provide the semantics of any particular choice of > instructions someone might expect to be used to implement the source code > - and in particular doesn't guarantee any choice of NaN where the language > (and IEEE 754 as applicable) don't determine the choice of NaN. I don't think the result of 0./0. in C code on a particular target should depend on telling the compiler that the runtime library is set up so that floating-point operations never trap. Brad
