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/s_logb.c | |
| parent | 021db4be6f1f4189f66feee066a495d49e92b93e (diff) | |
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/s_logb.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/s_logb.c | 37 |
1 files changed, 21 insertions, 16 deletions
diff --git a/sysdeps/ieee754/dbl-64/s_logb.c b/sysdeps/ieee754/dbl-64/s_logb.c index 2382fbb414..baa35e14d8 100644 --- a/sysdeps/ieee754/dbl-64/s_logb.c +++ b/sysdeps/ieee754/dbl-64/s_logb.c @@ -10,10 +10,6 @@ * ==================================================== */ -#if defined(LIBM_SCCS) && !defined(lint) -static char rcsid[] = "$NetBSD: s_logb.c,v 1.8 1995/05/10 20:47:50 jtc Exp $"; -#endif - /* * double logb(x) * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. @@ -23,20 +19,29 @@ static char rcsid[] = "$NetBSD: s_logb.c,v 1.8 1995/05/10 20:47:50 jtc Exp $"; #include <math.h> #include <math_private.h> -double __logb(double x) +double +__logb (double x) { - int32_t lx,ix; - EXTRACT_WORDS(ix,lx,x); - ix &= 0x7fffffff; /* high |x| */ - if((ix|lx)==0) return -1.0/fabs(x); - if(ix>=0x7ff00000) return x*x; - if((ix>>=20)==0) /* IEEE 754 logb */ - return -1022.0; - else - return (double) (ix-1023); + int32_t lx, ix, rix; + + EXTRACT_WORDS (ix, lx, x); + ix &= 0x7fffffff; /* high |x| */ + if ((ix | lx) == 0) + return -1.0 / fabs (x); + if (ix >= 0x7ff00000) + return x * x; + if (__builtin_expect ((rix = ix >> 20) == 0, 0)) + { + /* POSIX specifies that denormal number is treated as + though it were normalized. */ + int m1 = (ix == 0) ? 0 : __builtin_clz (ix); + int m2 = (lx == 0) ? 0 : __builtin_clz (lx); + int ma = (m1 == 0) ? m2 + 32 : m1; + return -1022.0 + (double)(11 - ma); + } + return (double) (rix - 1023); } weak_alias (__logb, logb) #ifdef NO_LONG_DOUBLE -strong_alias (__logb, __logbl) -weak_alias (__logb, logbl) +strong_alias (__logb, __logbl) weak_alias (__logb, logbl) #endif |