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
fnstenv MUST be followed by fldenv in fegetenv(), as the former disables all
exceptions in the x87 FPU, which is not appropriate here (fegetenv() ).
fldenv after fnstenv should reload the x87 FPU w/ the configuration that was
saved by fnstenv, i.e. a configuration that might have exceptions enabled.
Note: x86_64 uses SSE for floating-point, not the x87 FPU. However, because
feraiseexcept() attempts to provoke an exception using the x87 FPU, the bug
in fegetenv() will make this attempt futile here (x86_64).
Note: WoW uses the x87 FPU for floating-point, not SSE. Here anything that
would normally result in triggering an exception, not only feraiseexcept(),
will not be able to, as result of the bug in fegetenv().
Bump GPLv2+ to GPLv3+ for some files, clarify BSD 2-clause.
Everything else stays under GPLv3+.
New Linking Exception exempts resulting executables from LGPLv3 section 4.
Add CONTRIBUTORS file to keep track of licensing.
Remove 'Copyright Red Hat Inc' comments.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
On Linux and in Mingw-w64, fexcept_t is defined as type unsigned short.
There are packages in the wild which rely on the fact that fexcept_t is
an integral type. We're changing the internal handling to use the bits
just as in GLibc, so only the 6 lowest bits are used to reflect the hw
bits. We even change the header file guard to reflect GLibc for compatibility.
* include/fenv.h (_FENV_H): Rename from _FENV_H_ and set to 1 as in
GLibc's header.
(fexcept_t): Change to __uint16_t to be an integral type as in GLibc.
* fenv.cc (fegetexceptflag): Align to the *flagp's type change.
(fesetexceptflag): Ditto.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
J.H. van de Water
Corinna Vinschen
Jon Turney
Christopher Faylor
Dave Korn