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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/94111] Wrong constant folding: decimal
 floating-point infinity casted to double -> zero
Date: Wed, 11 Mar 2020 08:37:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94111

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
commit r10-7121-g312992f5a07ca25f94d538b08401789c2c764293
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Mar 11 09:33:52 2020 +0100

    dfp: Fix decimal_to_binary [PR94111]

    As e.g. decimal_from_decnumber shows, the REAL_VALUE_TYPE representation
    contains a decimal128 embedded in ->sig only if it is rvc_normal, for
    other kinds like rvc_inf or rvc_nan, ->sig is ignored and everything is
    contained in the REAL_VALUE_TYPE flags (cl, sign, signalling and decima=
l).
    decimal_to_binary which is used when folding a decimal{32,64,128} const=
ant
    to a binary floating point type ignores this and thus folds infinities =
and
    NaNs into +0.0.
    The following patch fixes that by only doing that for rvc_normal.
    Similarly to the binary to decimal folding, it goes through a string, in
    order to e.g. deal with canonical NaN mantissas, or binary float formats
    that don't support infinities and/or NaNs.

    2020-03-11  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/94111
            * dfp.c (decimal_to_binary): Only use decimal128ToString if
from->cl
            is rvc_normal, otherwise use real_to_decimal to print the numbe=
r to
            string.

            * gcc.dg/dfp/pr94111.c: New test.=