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| author | Joseph Myers <joseph@codesourcery.com> | 2014-06-10 12:07:15 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2014-06-10 12:07:15 +0000 |
| commit | f8ba1b5654d876c8db4c9a020e6fa976d434f988 (patch) | |
| tree | f5e34ce57471cbb1c54ec4cd0492b665f94151bb /sysdeps/x86_64 | |
| parent | 2c3520d98d9773d9e092196c3c36150244eed1dd (diff) | |
| download | glibc-f8ba1b5654d876c8db4c9a020e6fa976d434f988.zip glibc-f8ba1b5654d876c8db4c9a020e6fa976d434f988.tar.gz glibc-f8ba1b5654d876c8db4c9a020e6fa976d434f988.tar.bz2 | |
Fix log2 (1) in round-downward mode (bug 17042).
As with other issues of this kind, bug 17042 is log2 (1) wrongly
returning -0 instead of +0 in round-downward mode because of
implementations effectively in terms of log1p (x - 1). This patch
fixes the issue in the same way used for log and log10.
Tested x86_64 and x86 and ulps updated accordingly. Also tested for
mips64 to confirm a fix was needed for ldbl-128 and to validate that
fix (also applied to ldbl-128ibm since that version of log2l is
essentially the same as the ldbl-128 one).
[BZ #17042]
* sysdeps/i386/fpu/e_log2.S (__ieee754_log2): Take absolete value
when x - 1 is zero.
* sysdeps/i386/fpu/e_log2f.S (__ieee754_log2f): Likewise.
* sysdeps/i386/fpu/e_log2l.S (__ieee754_log2l): Likewise.
* sysdeps/ieee754/ldbl-128/e_log2l.c (__ieee754_log2l): Return
0.0L for an argument of 1.0L.
* sysdeps/ieee754/ldbl-128ibm/e_log2l.c (__ieee754_log2l):
Likewise.
* sysdeps/x86_64/fpu/e_log2l.S (__ieee754_log2l): Take absolute
value when x - 1 is zero.
* math/libm-test.inc (log2_test): Use ALL_RM_TEST.
* sysdeps/i386/fpu/libm-test-ulps: Update.
* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
Diffstat (limited to 'sysdeps/x86_64')
| -rw-r--r-- | sysdeps/x86_64/fpu/e_log2l.S | 8 | ||||
| -rw-r--r-- | sysdeps/x86_64/fpu/libm-test-ulps | 22 |
2 files changed, 29 insertions, 1 deletions
diff --git a/sysdeps/x86_64/fpu/e_log2l.S b/sysdeps/x86_64/fpu/e_log2l.S index 956489f..c12906d 100644 --- a/sysdeps/x86_64/fpu/e_log2l.S +++ b/sysdeps/x86_64/fpu/e_log2l.S @@ -45,7 +45,13 @@ ENTRY(__ieee754_log2l) fnstsw // x-1 : x : 1 andb $0x45, %ah jz 2f - fstp %st(1) // x-1 : 1 + fxam + fnstsw + andb $0x45, %ah + cmpb $0x40, %ah + jne 5f + fabs // log2(1) is +0 in all rounding modes. +5: fstp %st(1) // x-1 : 1 fyl2xp1 // log(x) ret diff --git a/sysdeps/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps index bb549d2..92fef5a 100644 --- a/sysdeps/x86_64/fpu/libm-test-ulps +++ b/sysdeps/x86_64/fpu/libm-test-ulps @@ -1665,6 +1665,28 @@ ifloat: 1 ildouble: 1 ldouble: 1 +Function: "log2_downward": +double: 2 +float: 2 +idouble: 2 +ifloat: 2 + +Function: "log2_towardzero": +double: 1 +float: 1 +idouble: 1 +ifloat: 1 +ildouble: 1 +ldouble: 1 + +Function: "log2_upward": +double: 2 +float: 2 +idouble: 2 +ifloat: 2 +ildouble: 1 +ldouble: 1 + Function: "log_downward": float: 1 ifloat: 1 |