[Bug tree-optimization/57994] Constant folding of infinity

[vincent-gcc at vinc17 dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57994

--- Comment #12 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Marc Glisse from comment #9)
> I believe there are far fewer special cases (and thus
> risks) with MPFR, but that would indeed require a suitable testsuite for all
> functions for which we enable it (at least if MPFR doesn't already have such
> a testsuite, and maybe even then, to make sure we call it properly).

MPFR's testsuite is just against the MPFR implementation. These are actually
non-regression tests. For comparisons with the functions from the C library,
there's mpcheck:

  https://gforge.inria.fr/projects/mpcheck/

but I don't know whether it includes special values (it wasn't its goal).

Note that we tried to follow C99's Annex F when this made sense. MPFR also
supports some special functions that are not in ISO C (yet), but may be
provided by the C library on some platforms (e.g. Bessel functions, which are
also specified in POSIX).

Don't forget that the specific rules for signed zeroes are also concerned;
again, we tried to follow C99's Annex F, IIRC, even when the specification was
rather inconsistent (e.g. under the rounding mode toward negative infinity, the
subtraction 1 - 1 returns -0, but log(1) is required to return +0).