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)?
Bruno
--
In memoriam Louis Philippe d'Orléans
<http://en.wikipedia.org/wiki/Louis_Philippe_II,_Duke_of_Orléans>
