[Bug math/30220] String to double returns incorrectly rounded value for hexadecimal subnormal

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30220

--- Comment #5 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The release/2.39/master branch has been updated by Arjun Shankar
<arjun@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a7be595c67d12f1a442e3f6894d67e20c7724bed

commit a7be595c67d12f1a442e3f6894d67e20c7724bed
Author: Joseph Myers <josmyers@redhat.com>
Date:   Tue Aug 27 12:41:02 2024 +0000

    Fix strtod subnormal rounding (bug 30220)

    As reported in bug 30220, the implementation of strtod-family
    functions has a bug in the following case: the input string would,
    with infinite exponent range, take one more bit to represent than is
    available in the normal precision of the return type; the value
    represented is in the subnormal range; and there are no nonzero bits
    in the value, below those that can be represented in subnormal
    precision, other than the least significant bit and possibly the
    0.5ulp bit.  In this case, round_and_return ends up discarding the
    least significant bit.

    Fix by saving that bit to merge into more_bits (it can't be merged in
    at the time it's computed, because more_bits mustn't include this bit
    in the case of after-rounding tininess detection checking if the
    result is still subnormal when rounded to normal precision, so merging
    this bit into more_bits needs to take place after that check).

    Tested for x86_64.

    (cherry picked from commit 457622c2fa8f9f7435822d5287a437bc8be8090d)

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