[Patch, fortran] PR 49010/24518 MOD/MODULO fixes

[Janne Blomqvist]

PING**2

On Wed, Mar 21, 2012 at 23:45, Janne Blomqvist
<blomqvist.janne@gmail.com> wrote:
> PING
>
> On Wed, Mar 14, 2012 at 01:03, Janne Blomqvist
> <blomqvist.janne@gmail.com> wrote:
>> Hi,
>>
>> the attached patch implements a few fixes and cleanups for the MOD and
>> MODULO intrinsics.
>>
>> - When the arguments are constant, use mpfr_fmod instead of the naive
>> algorithms which are numerically unstable for large arguments. This
>> extends the PR 24518 fix to constant arguments as well, and makes the
>> compile-time evaluation match the runtime implementation which also
>> uses fmod in the same manner.
>>
>> - Remove the old fallback path for the case builtin_fmod is not
>> available, as the builtin is AFAICS always available.
>>
>> The patch does not per se fix the corner-case bug as reported in PR
>> 49010, in fact it makes it worse in a way as with the patch the result
>> if the arguments are parameters is the same as the runtime result
>> (previously, the compile-time result was correct). But, I think we
>> should leave it as it is. Due to the reasons above, we're not using
>> the naive algorithms anyway, and IMHO -0.0 is quite a good
>> approximation for +0.0 anyway. One might even argue that due to the
>> numerical instability, specifying the naive algorithms is a bug in the
>> standard.
>>
>> The patch adds notes to the documentation about the usage of fmod, so
>> users interested in corner-case behavior can look up how that function
>> is supposed to behave on their target. FWIW, AFAICS MPFR and glibc
>> fmod conform to the behavior specified in C99 Annex F.
>>
>> Regtested on x86_64-unknown-linux-gnu, Ok for trunk?
>>
>> 2012-03-14  Janne Blomqvist  <jb@gcc.gnu.org>
>>
>>        PR fortran/49010
>>        PR fortran/24518
>>        * intrinsic.texi (MOD,MODULO): Mention usage of fmod instead of
>>        naive algorithm.
>>        * simplify.c (gfc_simplify_mod): Use mpfr_fmod.
>>        (gfc_simplify_modulo): Likewise.
>>        * trans-intrinsic.c (gfc_conv_intrinsic_mod): Remove fallback as
>>        builtin_fmod is always available.
>>
>>
>> --
>> Janne Blomqvist
>
>
>
> --
> Janne Blomqvist



-- 
Janne Blomqvist