[PATCH 1/1] Keep the denormal-operand exception masked; modify FE_ALL_EXCEPT accordingly.
Wed Aug 15 14:59:00 GMT 2018
On Aug 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.
Never mind, I just realize it's underscored so it's internal anyway.
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
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