On Sun, Nov 6, 2011 at 8:36 PM, Bruno Haible <br...@clisp.org> wrote:
> Hi,
>
> Considering how gnulib-implemented <math.h> functions should do their
> error reporting, I ran a test program to see how the various systems
> implement math errors.
>
> ============================================================================
> #include <errno.h>
> #include <math.h>
> #include <stdio.h>
> #ifndef NO_FENV
> #include <fenv.h>
> #endif
> int main()
> {
> double result;
> errno = 0;
> #ifndef NO_FENV
> fprintf (stderr, "before: %s\n",
> fetestexcept (FE_INVALID) ? "invalid" : "");
> #endif
> result = sqrt (-1.0);
> #ifndef NO_FENV
> fprintf (stderr, "%g, after: %s, errno=%d\n", result,
> fetestexcept (FE_INVALID) ? "invalid" : "", errno);
> #else
> fprintf (stderr, "%g, after: errno=%d\n", result, errno);
> #endif
> return 0;
> }
> ============================================================================
>
> The result:
>
> glibc 2.11: NaN, fenv bit, errno
> MacOS X 10.5: NaN, fenv bit math_errhandling
> (always=MATH_ERREXCEPT)
> FreeBSD 6.4: NaN, fenv bit math_errhandling
> (always=MATH_ERREXCEPT)
> OpenBSD 4.9: NaN
> NetBSD 5.1: NaN, errno
> AIX 7.1: NaN, fenv bit, errno math_errhandling (always=MATH_ERRNO)
> HP-UX 11.31: NaN, fenv bit, errno
> IRIX 6.5: NaN
> OSF/1 5.1: 0, errno (<fenv.h> incomplete)
> Solaris 10: NaN, fenv bit, errno math_errhandling
> (always=MATH_ERREXCEPT)
> Cygwin 1.7.9: NaN, errno
> mingw: NaN, fenv bit, errno
> MSVC 9: NaN, errno
>
> * All platforms except OSF/1 return a NaN value.
>
> * All platform that have a complete <fenv.h> (OSF/1 has an incomplete
> <fenv.h>) set the FE_INVALID bit in sqrt(-1).
>
> * Some platforms set errno, some don't.
>
> * math_errhandling is missing on many platforms. On those platforms where
> it is defined, it is useless, though:
> - All platforms that have math_errhandling also have <fenv.h>, therefore
> you don't need to consider math_errhandling if you want to know whether
> to set a floating-point exception bit.
> - Some of the platforms that set errno have a math_errhandling that
> includes MATH_ERRNO (AIX), some don't (Solaris).
>
> I am inclined to do the following in gnulib:
>
> 1) Provide a complete <fenv.h> on all platforms. glibc contains the code
> for the CPUs which are missing in the table above (x86, x86_64, sparc,
> mips, alpha).
>
> 2) Define math_errhandling everywhere, and override it on AIX and Solaris.
>
> How does that sound? (It's a lot of work, I know.)
>
> Is it likely that the IRIX, OSF/1, or MSVC compilers are implementing the
> math operators and functions in a way does not set the floating-point
> exception bits correctly (thus making <fenv.h> useless)?
msvc is compliant but a the microsoft taste
https://www.securecoding.cert.org/confluence/display/seccode/FLP03-C.+Detect+and+handle+floating+point+errors
and
http://msdn.microsoft.com/en-us/library/te2k2f2t%28v=vs.80%29.aspx
Bastien
> Bruno
> --
> In memoriam Louis Philippe d'Orléans
> <http://en.wikipedia.org/wiki/Louis_Philippe_II,_Duke_of_Orléans>
>
>
