diff options
author | Adhemerval Zanella <azanella@linux.vnet.ibm.com> | 2012-05-10 15:11:55 -0500 |
---|---|---|
committer | Ryan S. Arnold <rsa@linux.vnet.ibm.com> | 2012-05-10 15:11:55 -0500 |
commit | 89c9aa491a7cee97bf78a29cddbf0a25c902a671 (patch) | |
tree | a03f7f7a4864421a67c1f4ba3c4ad74090cc0e63 /sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c | |
parent | 021db4be6f1f4189f66feee066a495d49e92b93e (diff) | |
download | glibc-89c9aa491a7cee97bf78a29cddbf0a25c902a671.tar.gz glibc-89c9aa491a7cee97bf78a29cddbf0a25c902a671.tar.xz glibc-89c9aa491a7cee97bf78a29cddbf0a25c902a671.zip |
Fix for logb/logbf/logbl (bugs 13954/13955/13956)
POSIX 2008 states that if the input for 'logb[f|l]' is a subnormal number it should be treated as if it were normalized. This means the implementation should calculate the log2 of the mantissa and add it to the subnormal exponent (-126 for float and -1022 for double and IBM long double). This patch takes care of that.
Diffstat (limited to 'sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c')
-rw-r--r-- | sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c index 2ad6c7ddbd..474eeef36b 100644 --- a/sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c +++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c @@ -1,5 +1,5 @@ /* Compute radix independent exponent. - Copyright (C) 2011 Free Software Foundation, Inc. + Copyright (C) 2011, 2012 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Ulrich Drepper <drepper@gmail.com>, 2011. @@ -25,16 +25,21 @@ double __logb (double x) { - int64_t ix; + int64_t ix, ex; EXTRACT_WORDS64 (ix, x); ix &= UINT64_C(0x7fffffffffffffff); if (ix == 0) return -1.0 / fabs (x); - unsigned int ex = ix >> 52; + ex = ix >> 52; if (ex == 0x7ff) return x * x; - return ex == 0 ? -1022.0 : (double) (ex - 1023); + if (__builtin_expect (ex == 0, 0)) + { + int m = (ix == 0) ? 0 : __builtin_clzl (ix); + return -1022.0 + (double)(11 -m); + } + return (double) (ex - 1023); } weak_alias (__logb, logb) #ifdef NO_LONG_DOUBLE |