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| author | Joseph Myers <joseph@codesourcery.com> | 2014-03-21 18:13:58 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2014-03-21 18:13:58 +0000 |
| commit | f7be737659813220e1f29c8850c386a9654d549a (patch) | |
| tree | c047f314e8eca5df155322e4fe9471593fb07b67 /sysdeps/ieee754 | |
| parent | a387428ca7330513d5f2a0924c45e6382d477052 (diff) | |
| download | glibc-f7be737659813220e1f29c8850c386a9654d549a.zip glibc-f7be737659813220e1f29c8850c386a9654d549a.tar.gz glibc-f7be737659813220e1f29c8850c386a9654d549a.tar.bz2 | |
Fix log (1) in round-downward mode (bug 16731).
According to ISO C Annex F, log (1) should be +0 in all rounding
modes, but some implementations in glibc wrongly return -0 in
round-downward mode (mapping to log1p (x - 1) is problematic because 1
- 1 is -0 in round-downward mode, and log1p (-0) is -0). This patch
fixes this. (It helps with some implementations of other functions
such as acosh, log2 and log10 that call out to log, but not enough to
enable all-rounding-modes testing for those functions without further
fixes to other implementations of them.)
Tested x86_64 and x86 and ulps updated accordingly, and did spot tests
for mips64 for the ldbl-128 fix, and i586 for the sysdeps/i386/fpu
implementations shadowed by those in sysdeps/i386/i686/fpu.
[BZ #16731]
* sysdeps/i386/fpu/e_log.S (__ieee754_log): Take absolute value
when x - 1 is zero.
* sysdeps/i386/fpu/e_logf.S (__ieee754_logf): Likewise.
* sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Likewise.
* sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise.
* sysdeps/ieee754/dbl-64/e_log.c (__ieee754_log): Return +0 when
argument is 1.
* sysdeps/ieee754/ldbl-128/e_logl.c (__ieee754_logl): Likewise.
* sysdeps/x86_64/fpu/e_logl.S: Take absolute value when x - 1 is
zero.
* math/libm-test.inc (log_test): Use ALL_RM_TEST.
* sysdeps/i386/fpu/libm-test-ulps: Update.
* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
Diffstat (limited to 'sysdeps/ieee754')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/e_log.c | 4 | ||||
| -rw-r--r-- | sysdeps/ieee754/ldbl-128/e_logl.c | 2 |
2 files changed, 6 insertions, 0 deletions
diff --git a/sysdeps/ieee754/dbl-64/e_log.c b/sysdeps/ieee754/dbl-64/e_log.c index 05d318b..4ecd372 100644 --- a/sysdeps/ieee754/dbl-64/e_log.c +++ b/sysdeps/ieee754/dbl-64/e_log.c @@ -96,6 +96,10 @@ __ieee754_log (double x) if (__glibc_likely (ABS (w) > U03)) goto case_03; + /* log (1) is +0 in all rounding modes. */ + if (w == 0.0) + return 0.0; + /*--- Stage I, the case abs(x-1) < 0.03 */ t8 = MHALF * w; diff --git a/sysdeps/ieee754/ldbl-128/e_logl.c b/sysdeps/ieee754/ldbl-128/e_logl.c index 3d1034d..cb43816 100644 --- a/sysdeps/ieee754/ldbl-128/e_logl.c +++ b/sysdeps/ieee754/ldbl-128/e_logl.c @@ -240,6 +240,8 @@ __ieee754_logl(long double x) /* On this interval the table is not used due to cancellation error. */ if ((x <= 1.0078125L) && (x >= 0.9921875L)) { + if (x == 1.0L) + return 0.0L; z = x - 1.0L; k = 64; t.value = 1.0L; |