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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/i386 | |
| parent | e7dd3c8c1db8c6d293abb995e033893b7328ad19 (diff) | |
| download | glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.tar.gz glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.tar.xz glibc-4060283decf711ed95a6c4993ffeaba39f8cd40a.zip | |
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/i386')
| -rw-r--r-- | sysdeps/i386/fpu/e_expl.S | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/sysdeps/i386/fpu/e_expl.S b/sysdeps/i386/fpu/e_expl.S index eb4086b3f5..c7e43732dc 100644 --- a/sysdeps/i386/fpu/e_expl.S +++ b/sysdeps/i386/fpu/e_expl.S @@ -108,6 +108,16 @@ ENTRY(IEEE754_EXPL) andb %ah, %dh cmpb $0x40, %dh je 2f + + /* Test for arguments that are small but not subnormal. */ + movzwl 4+8(%esp), %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 4+8(%esp), %eax andl $0x7fff, %eax |