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| author | Joseph Myers <joseph@codesourcery.com> | 2015-09-30 23:34:59 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2015-09-30 23:34:59 +0000 |
| commit | 7cda516f5f23772fd37ca3a5e018fca5bf388435 (patch) | |
| tree | 1a344d2d855f73e86ac7d9e056ea6e08f24ad777 /sysdeps/ieee754 | |
| parent | 8c6c9236361fbc077769673c259828216403bc33 (diff) | |
| download | glibc-7cda516f5f23772fd37ca3a5e018fca5bf388435.tar.gz glibc-7cda516f5f23772fd37ca3a5e018fca5bf388435.tar.xz glibc-7cda516f5f23772fd37ca3a5e018fca5bf388435.zip | |
Fix ldbl-128ibm exp10l spurious overflows (bug 16620).
The ldbl-128ibm implementation of exp10l uses a version of log(10) split into high and low parts - but the low part is negative, so causing spurious overflows from __ieee754_expl (exp_high) in cases close to the overflow threshold (I added relevant tests close to the overflow threshold to the testsuite earlier today). The same issue applies close to the underflow threshold as well (except that spurious underflows in IBM long double arithmetic are harder to fix than the other deficiencies, so we might end up permitting those for IBM long double in the libm testsuite, as permitted by ISO C). This patch fixes it to use a low part rounded downward to 48 bits instead. (The choice of 48 instead of 53 bits is to make it more obviously safe even when the low part of the argument is negative.) Tested for powerpc. (Note that because of libgcc bugs with multiplication very close to LDBL_MAX, libgcc also needs patching for all the problem cases to be fixed, but this patch is still safe and correct in the absence of such libgcc fixes.) [BZ #16620] * sysdeps/ieee754/ldbl-128ibm/e_exp10l.c (log10_high): Use value of log (10) rounded downward to 48 bits. (log10_low): Use corresponding low part of log (10).
Diffstat (limited to 'sysdeps/ieee754')
| -rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/e_exp10l.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_exp10l.c b/sysdeps/ieee754/ldbl-128ibm/e_exp10l.c index deefe7f54f..e1f0cbbc9f 100644 --- a/sysdeps/ieee754/ldbl-128ibm/e_exp10l.c +++ b/sysdeps/ieee754/ldbl-128ibm/e_exp10l.c @@ -19,8 +19,8 @@ #include <math_private.h> #include <float.h> -static const long double log10_high = 0x2.4d763776aaa2cp0L; -static const long double log10_low = -0xf.a456a4a751f4b3d75c75c04c18p-56L; +static const long double log10_high = 0x2.4d763776aaap+0L; +static const long double log10_low = 0x2.b05ba95b58ae0b4c28a38a3fb4p-48L; long double __ieee754_exp10l (long double arg) |