This is the mail archive of the glibc-bugs@sourceware.org mailing list for the glibc project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[Bug math/18981] i386 scalb*, ldexp return with excess range and precision


https://sourceware.org/bugzilla/show_bug.cgi?id=18981

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  94ced920a951bcab51f2ef955ccd2cc51668e6f3 (commit)
      from  89faa0340ad399ead8104f8fb6b7fed81f7d939c (commit)

Those revisions listed above that are new to this repository have
not appeared on any other notification email; so we list those
revisions in full, below.

- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=94ced920a951bcab51f2ef955ccd2cc51668e6f3

commit 94ced920a951bcab51f2ef955ccd2cc51668e6f3
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Sep 18 20:34:59 2015 +0000

    Avoid excess range in results from i386 scalb functions (bug 18981).

    i386 scalb / scalbn / scalbln (and thus ldexp) functions for float and
    double can return results with excess range (and consequently excess
    precision for subnormal results).  As the results of these functions
    are fully determined by reference to IEEE 754 operations, this is
    unambiguously a bug, apart from the testsuite failures it causes.

    This patch makes those functions store their results on the stack and
    load them back to eliminate the excess range.  Double rounding is not
    a problem, as the only cases where it could occur are when the result
    overflows or underflows for extended precision, and then the
    double-rounded results are the same as the single-rounded results.

    The new macros will be used for more functions, more such macros
    added, and existing code refactored to use such macros, in subsequent
    patches.

    Tested for x86.  Committed.

        [BZ #18981]
        * sysdeps/i386/fpu/i386-math-asm.h: New file.
        * sysdeps/i386/fpu/e_scalb.S: Include <i386-math-asm.h>.
        (__ieee754_scalb): Use DBL_NARROW_EVAL.
        * sysdeps/i386/fpu/e_scalbf.S: Include <i386-math-asm.h>.
        (__ieee754_scalbf): Use FLT_NARROW_EVAL.
        * sysdeps/i386/fpu/s_scalbn.S: Include <i386-math-asm.h>.
        (__scalbn): Use DBL_NARROW_EVAL.
        * sysdeps/i386/fpu/s_scalbnf.S: Include <i386-math-asm.h>.
        (__scalbnf): Use FLT_NARROW_EVAL.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                          |   13 +++++++++
 NEWS                                               |    2 +-
 sysdeps/i386/fpu/e_scalb.S                         |    2 +
 sysdeps/i386/fpu/e_scalbf.S                        |    2 +
 .../i386/fpu/i386-math-asm.h                       |   29 +++++++++++++------
 sysdeps/i386/fpu/s_scalbn.S                        |    2 +
 sysdeps/i386/fpu/s_scalbnf.S                       |    2 +
 7 files changed, 42 insertions(+), 10 deletions(-)
 copy benchtests/bench-util.h => sysdeps/i386/fpu/i386-math-asm.h (58%)

-- 
You are receiving this mail because:
You are on the CC list for the bug.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]