Re: math error reporting

[Bruno Haible]

> In November 2011, I wrote in
> <http://lists.gnu.org/archive/html/bug-gnulib/2011-11/msg00069.html>:
> 
>    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

Actually glibc does not support the 'errno' convention really.
See this list of bugs: [1]
The following are still open:
6796 fdim() does not set errno on overflow
6785 erf() does not set errno for underflow
6793 logb() does not set errno on pole error
6804 scalb() does not set errno on domain error
6808 yn() does not set errno for overflow error.
6802 remquo() does not set errno on domain error
6792 log1p() does not set errno n error
6801 fma() does not ser errno for various errors
6797 lround() and llround() do not set errno on domain error
6786 erfc() does not set errno for underflow
6798 lrint() and llrint() do not set errno on domain error
6810 tgamma() does not set errno for underflow error
6809 tgamma() sets errno inconsistently for domain error
6795 hypot() does not set errno consistently on error
6787 exp10() does not consistently set errno
6799 nextafter() and nexttoward() doen't set errno on overflow/underflow errors
6807 y0(), y1(), yn() do not raise exception and give wrong errno for pole error
6794 ilogb() does not raise exceptions or set errno on domain errors
6803 scalb(), scalbln(), scalbn() do not set errno on overflow/underflow
6805 j0(), j1(), jn() do not raise exceptions on underflow error
6806 y0(), y1(), yn() do not raise exception on underflow

If glibc does not support this error reporting convention, I think there's
not much point for gnulib to do it.

Btw, a side note about the "fenv bit" convention:
  1) "inexact" and "underflow" exceptions cannot be taken seriously
     because Joseph Myers sais [2]:
       "C99 and C11 permit spurious underflow exceptions (as well as
        spurious inexact exceptions, and raising inexact even when
        the result is exact)."
  2) glibc has some open bugs in this area as well: [3]

Bruno

[1] 
http://sourceware.org/bugzilla/buglist.cgi?query_format=specific&order=relevance%20desc&bug_status=__all__&content=math%20errno&list_id=3078
[2] http://sourceware.org/bugzilla/show_bug.cgi?id=6778
[3] http://sourceware.org/bugzilla/show_bug.cgi?id=13787