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| author | Joseph Myers <joseph@codesourcery.com> | 2014-06-24 21:00:08 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2014-06-24 21:00:08 +0000 |
| commit | 4060283decf711ed95a6c4993ffeaba39f8cd40a (patch) | |
| tree | d303f8bcf7bd9fafbbb5edddc48c7c2be827f84e /sysdeps/x86_64/fpu | |
| parent | e7dd3c8c1db8c6d293abb995e033893b7328ad19 (diff) | |
| download | glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.zip glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.tar.gz glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.tar.bz2 | |
Fix x86/x86_64 expm1l spurious underflow exceptions (bug 16539).
This patch fixes bug 16539, spurious underflow exceptions from x86 /
x86-64 expm1l. The problem is that the computation of a base-2
exponent with extra precision involves spurious underflows for
arguments that are small but not subnormal, so a check is added to
just return the argument in those cases. (If the argument *is*
subnormal, underflowing is correct and the existing code will always
underflow, so it suffices to keep using the existing code in that
case; some expm1 implementations have a bug (bug 16353) with missing
underflow exceptions, but I don't think there's such a bug in this
particular version.)
Tested x86_64 and x86; no ulps updates needed.
(auto-libm-test-out diffs omitted below.)
[BZ #16539]
* sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Just
return the argument for normal arguments with exponent below -64.
* sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
Likewise.
* math/auto-libm-test-in: Add another test of expm1.
* math/auto-libm-test-out: Regenerated.
Diffstat (limited to 'sysdeps/x86_64/fpu')
| -rw-r--r-- | sysdeps/x86_64/fpu/e_expl.S | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/sysdeps/x86_64/fpu/e_expl.S b/sysdeps/x86_64/fpu/e_expl.S index 338527b..0ebe388 100644 --- a/sysdeps/x86_64/fpu/e_expl.S +++ b/sysdeps/x86_64/fpu/e_expl.S @@ -105,6 +105,16 @@ ENTRY(IEEE754_EXPL) andb %ah, %dh cmpb $0x40, %dh je 2f + + /* Test for arguments that are small but not subnormal. */ + movzwl 8+8(%rsp), %eax + andl $0x7fff, %eax + cmpl $0x3fbf, %eax + jge 3f + /* Argument's exponent below -64; avoid spurious underflow if + normal. */ + cmpl $0x0001, %eax + jge 2f #else movzwl 8+8(%rsp), %eax andl $0x7fff, %eax |