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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/i386 | |
| parent | 2c3520d98d9773d9e092196c3c36150244eed1dd (diff) | |
| download | glibc-f8ba1b5654d876c8db4c9a020e6fa976d434f988.tar.gz glibc-f8ba1b5654d876c8db4c9a020e6fa976d434f988.tar.xz glibc-f8ba1b5654d876c8db4c9a020e6fa976d434f988.zip | |
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/i386')
| -rw-r--r-- | sysdeps/i386/fpu/e_log2.S | 8 | ||||
| -rw-r--r-- | sysdeps/i386/fpu/e_log2f.S | 8 | ||||
| -rw-r--r-- | sysdeps/i386/fpu/e_log2l.S | 8 | ||||
| -rw-r--r-- | sysdeps/i386/fpu/libm-test-ulps | 16 |
4 files changed, 37 insertions, 3 deletions
diff --git a/sysdeps/i386/fpu/e_log2.S b/sysdeps/i386/fpu/e_log2.S index a202bc731d..73ff0fffd3 100644 --- a/sysdeps/i386/fpu/e_log2.S +++ b/sysdeps/i386/fpu/e_log2.S @@ -47,7 +47,13 @@ ENTRY(__ieee754_log2) 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/i386/fpu/e_log2f.S b/sysdeps/i386/fpu/e_log2f.S index f4f9a8c3bf..344eeb495e 100644 --- a/sysdeps/i386/fpu/e_log2f.S +++ b/sysdeps/i386/fpu/e_log2f.S @@ -47,7 +47,13 @@ ENTRY(__ieee754_log2f) 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/i386/fpu/e_log2l.S b/sysdeps/i386/fpu/e_log2l.S index bd51b5651e..0f5f7e5789 100644 --- a/sysdeps/i386/fpu/e_log2l.S +++ b/sysdeps/i386/fpu/e_log2l.S @@ -47,7 +47,13 @@ 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/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps index 1e89284455..d7424a6f86 100644 --- a/sysdeps/i386/fpu/libm-test-ulps +++ b/sysdeps/i386/fpu/libm-test-ulps @@ -1588,6 +1588,22 @@ ifloat: 1 ildouble: 1 ldouble: 1 +Function: "log2_towardzero": +double: 1 +float: 1 +idouble: 1 +ifloat: 1 +ildouble: 1 +ldouble: 1 + +Function: "log2_upward": +double: 1 +float: 1 +idouble: 1 +ifloat: 1 +ildouble: 1 +ldouble: 1 + Function: "log_downward": ildouble: 1 ldouble: 1 |