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authorJoseph Myers <joseph@codesourcery.com>2014-06-24 21:00:08 +0000
committerJoseph Myers <joseph@codesourcery.com>2014-06-24 21:00:08 +0000
commit4060283decf711ed95a6c4993ffeaba39f8cd40a (patch)
treed303f8bcf7bd9fafbbb5edddc48c7c2be827f84e /sysdeps/x86_64
parente7dd3c8c1db8c6d293abb995e033893b7328ad19 (diff)
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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')
-rw-r--r--sysdeps/x86_64/fpu/e_expl.S10
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