On Aug 15 17:01, Houder wrote: > On 2018-08-15 16:54, Corinna Vinschen wrote: > > On Aug 15 12:59, J.H. van de Water wrote: > > > By excluding the denormal-operand exception from FE_ALL_EXCEPT, it > > > will not > > > be possible anymore to UNmask this exception by means of the API > > > defined by > > > /usr/include/fenv.h > > > > > > Note: terminology has changed since IEEE Std 854-1987; denormalized > > > numbers > > > are called subnormal numbers nowadays. > > > > > > This modification has basically been motivated by the fact that it > > > is also > > > not possible on Linux to manipulate the denormal-operand exception > > > by means > > > of the interface as defined by /usr/include/fenv.h. This has been > > > the state > > > of affairs on Linux since 2001 (Andreas Jaeger). > > > > > > The exceptions required by the standard (IEEE Std 754), in case they > > > can be > > > supported by the implementation, are: > > > FE_INEXACT, FE_UNDERFLOW, FE_OVERFLOW, FE_DIVBYZERO and FE_INVALID. > > > > > > Although it is allowed to define additional exceptions, there is no > > > reason > > > to support the "denormal-operand exception" in this case (fenv.h), > > > because > > > the subnormal numbers can be handled almost as fast the normalized > > > numbers > > > by the hardware of the x86/x86_64 architecture. Said differently, a > > > reason > > > to trap on the input of subnormal numbers does not exist. At least > > > that is > > > what William Kahan and others at Intel asserted around 2000. > > > (that is William Kahan of the K-C-S draft, the precursor to the > > > standard) > > > > > > This commit modifies winsup/cygwin/include/fenv.h as follows: > > > - redefines FE_ALL_EXCEPT from 0x3f to 0x3d > > > - removes the definition for FE_DENORMAL > > > - introduces __FE_DENORM (0x2) (enum in Linux also uses __FE_DENORM) > > > - introduces FE_ALL_EXCEPT_X86 (0x3f), i.e. ALL x86/x86_64 FP > > > exceptions > > > > Shouldn't FE_ALL_EXCEPT_X86 be defined locally in fenv.cc only? > > I don't see that Linux exports that definition. > > Ah, Sorry. Do I have to resubmit my patch? Or is it easy enough for you to > make this modification?
It's easy enough but I'm still mulling over __FE_DENORM. The glibc fenv.h header defines it, so I guess we should stick to it. In that case it might make sense to revert the original comment and just move __FE_ALL_EXCEPT_X86. Ok? Thanks, Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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