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| author | Joseph Myers <joseph@codesourcery.com> | 2014-06-18 12:32:01 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2014-06-18 12:32:01 +0000 |
| commit | 4ba7a00fe3779e6ffafad6d47305b3491cdac33e (patch) | |
| tree | 8735df5c818ab5022e97f53c3fd69be723299a45 /sysdeps/x86_64 | |
| parent | b3a9f56ba59c3d8eadd3135a1c25c37a63151450 (diff) | |
| download | glibc-4ba7a00fe3779e6ffafad6d47305b3491cdac33e.tar.gz glibc-4ba7a00fe3779e6ffafad6d47305b3491cdac33e.tar.xz glibc-4ba7a00fe3779e6ffafad6d47305b3491cdac33e.zip | |
Fix __ieee754_logl (-LDBL_MAX) in FE_DOWNWARD mode (bug 17022).
This patch fixes __ieee754_logl (-LDBL_MAX) on x86_64 and x86 not to subtract 1 from its argument and so cause spurious overflow in FE_DOWNWARD mode. (For any argument strictly less than -1, it doesn't matter whether or not 1 is subtracted before computing log1p, as long as the result doesn't overflow to -Inf.) Tested x86_64 and x86. (This particular case lacks test coverage, since the testsuite doesn't cover -lieee, but it will be covered by tests after the following patch to test pow in all rounding modes, which was the context in which this bug was found.) [BZ #17022] * sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Do not subtract 1 from arguments -2 or below. * sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise. * sysdeps/x86_64/fpu/e_logl.S (__ieee754_logl): Likewise.
Diffstat (limited to 'sysdeps/x86_64')
| -rw-r--r-- | sysdeps/x86_64/fpu/e_logl.S | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/sysdeps/x86_64/fpu/e_logl.S b/sysdeps/x86_64/fpu/e_logl.S index 315afc0033..047b8db88a 100644 --- a/sysdeps/x86_64/fpu/e_logl.S +++ b/sysdeps/x86_64/fpu/e_logl.S @@ -38,8 +38,11 @@ ENTRY(__ieee754_logl) fld %st // x : x : log(2) testb $1, %ah jnz 3f // in case x is NaN or +-Inf + movzwl 8+8(%rsp), %eax + cmpl $0xc000, %eax + jae 6f // x <= -2, avoid overflow from -LDBL_MAX - 1. 4: fsubl MO(one) // x-1 : x : log(2) - fld %st // x-1 : x-1 : x : log(2) +6: fld %st // x-1 : x-1 : x : log(2) fabs // |x-1| : x-1 : x : log(2) fcompl MO(limit) // x-1 : x : log(2) fnstsw // x-1 : x : log(2) |