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.

9 files changed, 143 insertions, 74 deletions

diff --git a/ChangeLog b/ChangeLog
index 8bceaab..6848fb4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2012-05-09  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
+
+	[BZ #13954]
+	[BZ #13955]
+	[BZ #13956]
+	* sysdeps/ieee754/dbl-64/s_logb.c (__logb): Fix for subnormal number.
+	* sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c (__logb): Likewise.
+	* sysdeps/ieee754/flt-32/s_logbf.c (__logf): Likewise.
+	* sysdeps/ieee754/ldbl-128/s_logbl.c (__logbl): Likewise.
+	* sysdeps/ieee754/ldbl-128ibm/s_logbl.c (__logbl): Likewise.
+	* sysdeps/ieee754/ldbl-96/s_logbl.c (__logbl): Likewise.
+	* math/libm-test.inc (logb_test) : Additional logb tests.
+
 2012-05-09  Andreas Schwab  <schwab@linux-m68k.org>
 	    Andreas Jaeger  <aj@suse.de>
 
diff --git a/NEWS b/NEWS
index 5c90f3d..b3a1233 100644
--- a/NEWS
+++ b/NEWS
@@ -23,8 +23,9 @@ Version 2.16
   13852, 13854, 13871, 13872, 13873, 13879, 13883, 13884, 13885, 13886,
   13892, 13895, 13908, 13910, 13911, 13912, 13913, 13914, 13915, 13916,
   13917, 13918, 13919, 13920, 13921, 13922, 13923, 13924, 13926, 13927,
-  13928, 13938, 13941, 13942, 13963, 13967, 13970, 13973, 13979, 13983,
-  14027, 14033, 14034, 14040, 14049, 14053, 14055, 14064, 14080, 14083
+  13928, 13938, 13941, 13942, 13954, 13955, 13956, 13963, 13967, 13970,
+  13973, 13979, 13983, 14027, 14033, 14034, 14040, 14049, 14053, 14055,
+  14064, 14080, 14083
 
 * ISO C11 support:
 
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 542131d..5a38dbf 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -5376,6 +5376,22 @@ logb_test (void)
   TEST_f_f (logb, 1024, 10);
   TEST_f_f (logb, -2000, 10);
 
+  TEST_f_f (logb, 0x0.1p-127, -131);
+  TEST_f_f (logb, 0x0.01p-127, -135);
+  TEST_f_f (logb, 0x0.011p-127, -135);
+#ifndef TEST_FLOAT
+  TEST_f_f (logb, 0x0.8p-1022, -1023);
+  TEST_f_f (logb, 0x0.1p-1022, -1026);
+  TEST_f_f (logb, 0x0.00111p-1022, -1034);
+  TEST_f_f (logb, 0x0.00001p-1022, -1042);
+  TEST_f_f (logb, 0x0.000011p-1022, -1042);
+  TEST_f_f (logb, 0x0.0000000000001p-1022, -1074);
+#endif
+#if defined TEST_LDOUBLE && LDBL_MIN_EXP - LDBL_MANT_DIG <= -16400
+  TEST_f_f (logb, 0x1p-16400L, -16400);
+  TEST_f_f (logb, 0x.00000000001p-16382L, -16426);
+#endif
+
   END (logb);
 }
 
diff --git a/sysdeps/ieee754/dbl-64/s_logb.c b/sysdeps/ieee754/dbl-64/s_logb.c
index 2382fbb..baa35e1 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
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c
index 2ad6c7d..474eeef 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
diff --git a/sysdeps/ieee754/flt-32/s_logbf.c b/sysdeps/ieee754/flt-32/s_logbf.c
index b6aa0f0..025c70d 100644
--- a/sysdeps/ieee754/flt-32/s_logbf.c
+++ b/sysdeps/ieee754/flt-32/s_logbf.c
@@ -13,23 +13,27 @@
  * ====================================================
  */
 
-#if defined(LIBM_SCCS) && !defined(lint)
-static char rcsid[] = "$NetBSD: s_logbf.c,v 1.4 1995/05/10 20:47:51 jtc Exp $";
-#endif
-
 #include <math.h>
 #include <math_private.h>
 
-float __logbf(float x)
+float
+__logbf (float x)
 {
-	int32_t ix;
-	GET_FLOAT_WORD(ix,x);
-	ix &= 0x7fffffff;			/* high |x| */
-	if(ix==0) return (float)-1.0/fabsf(x);
-	if(ix>=0x7f800000) return x*x;
-	if((ix>>=23)==0) 			/* IEEE 754 logb */
-		return -126.0; 
-	else
-		return (float) (ix-127); 
+  int32_t ix, rix;
+
+  GET_FLOAT_WORD (ix, x);
+  ix &= 0x7fffffff;		/* high |x| */
+  if (ix == 0)
+    return (float) -1.0 / fabsf (x);
+  if (ix >= 0x7f800000)
+    return x * x;
+  if (__builtin_expect ((rix = ix >> 23) == 0, 0))
+    {
+      /* POSIX specifies that denormal number is treated as
+         though it were normalized.  */
+      int m = (ix == 0) ? 0 : __builtin_clz (ix);
+      return -126.0 + (float)(8 - m);
+    }
+  return (float) (rix - 127);
 }
 weak_alias (__logbf, logbf)
diff --git a/sysdeps/ieee754/ldbl-128/s_logbl.c b/sysdeps/ieee754/ldbl-128/s_logbl.c
index 0b09b28..cf6003e 100644
--- a/sysdeps/ieee754/ldbl-128/s_logbl.c
+++ b/sysdeps/ieee754/ldbl-128/s_logbl.c
@@ -26,16 +26,27 @@ static char rcsid[] = "$NetBSD: $";
 #include <math.h>
 #include <math_private.h>
 
-long double __logbl(long double x)
+long double
+__logbl (long double x)
 {
-	int64_t lx,hx;
-	GET_LDOUBLE_WORDS64(hx,lx,x);
-	hx &= 0x7fffffffffffffffLL;		/* high |x| */
-	if((hx|lx)==0) return -1.0/fabs(x);
-	if(hx>=0x7fff000000000000LL) return x*x;
-	if((hx>>=48)==0) 			/* IEEE 754 logb */
-		return -16382.0;
-	else
-		return (long double) (hx-0x3fff);
+  int64_t lx, hx, ex;
+
+  GET_LDOUBLE_WORDS64 (hx, lx, x);
+  hx &= 0x7fffffffffffffffLL;	/* high |x| */
+  if ((hx | lx) == 0)
+    return -1.0 / fabs (x);
+  if (hx >= 0x7fff000000000000LL)
+    return x * x;
+  if ((ex = hx >> 48) == 0)	/* IEEE 754 logb */
+    {
+      /* POSIX specifies that denormal number is treated as
+         though it were normalized.  */
+      int m1 = (hx == 0) ? 0 : __builtin_clzll (hx);
+      int m2 = (lx == 0) ? 0 : __builtin_clzll (lx);
+      int ma = (m1 == 0) ? m2 + 64 : m1;
+      return -16382.0 + (long double)(15 - ma);
+    }
+  return (long double) (ex - 16383);
 }
+
 weak_alias (__logbl, logbl)
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_logbl.c b/sysdeps/ieee754/ldbl-128ibm/s_logbl.c
index f38b129..678b6ca 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_logbl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_logbl.c
@@ -13,10 +13,6 @@
  * ====================================================
  */
 
-#if defined(LIBM_SCCS) && !defined(lint)
-static char rcsid[] = "$NetBSD: $";
-#endif
-
 /*
  * long double logbl(x)
  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
@@ -27,16 +23,27 @@ static char rcsid[] = "$NetBSD: $";
 #include <math_private.h>
 #include <math_ldbl_opt.h>
 
-long double __logbl(long double x)
+long double
+__logbl (long double x)
 {
-	int64_t lx,hx;
-	GET_LDOUBLE_WORDS64(hx,lx,x);
-	hx &= 0x7fffffffffffffffLL;		/* high |x| */
-	if((hx|(lx&0x7fffffffffffffffLL))==0) return -1.0/fabs(x);
-	if(hx>=0x7ff0000000000000LL) return x*x;
-	if((hx>>=52)==0) 			/* IEEE 754 logb */
-		return -1022.0;
-	else
-		return (long double) (hx-0x3ff);
+  int64_t lx, hx, rhx;
+
+  GET_LDOUBLE_WORDS64 (hx, lx, x);
+  hx &= 0x7fffffffffffffffLL;	/* high |x| */
+  if ((hx | (lx & 0x7fffffffffffffffLL)) == 0)
+    return -1.0 / fabs (x);
+  if (hx >= 0x7ff0000000000000LL)
+    return x * x;
+  if (__builtin_expect ((rhx = hx >> 52) == 0, 0))
+    {
+      /* POSIX specifies that denormal number is treated as
+         though it were normalized.  */
+      int m1 = (hx == 0) ? 0 : __builtin_clzll (hx);
+      int m2 = (lx == 0) ? 0 : __builtin_clzll (lx);
+      int ma = (m1 == 0) ? m2 + 64 : m1;
+      return -1022.0 + (long double)(11 - ma);
+    }
+  return (long double) (rhx - 1023);
 }
+
 long_double_symbol (libm, __logbl, logbl);
diff --git a/sysdeps/ieee754/ldbl-96/s_logbl.c b/sysdeps/ieee754/ldbl-96/s_logbl.c
index 95b644c..d8ad4bc 100644
--- a/sysdeps/ieee754/ldbl-96/s_logbl.c
+++ b/sysdeps/ieee754/ldbl-96/s_logbl.c
@@ -14,10 +14,6 @@
  * ====================================================
  */
 
-#if defined(LIBM_SCCS) && !defined(lint)
-static char rcsid[] = "$NetBSD: $";
-#endif
-
 /*
  * long double logbl(x)
  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
@@ -27,16 +23,27 @@ static char rcsid[] = "$NetBSD: $";
 #include <math.h>
 #include <math_private.h>
 
-long double __logbl(long double x)
+long double
+__logbl (long double x)
 {
-	int32_t es,lx,ix;
-	GET_LDOUBLE_WORDS(es,ix,lx,x);
-	es &= 0x7fff;				/* exponent */
-	if((es|ix|lx)==0) return -1.0/fabs(x);
-	if(es==0x7fff) return x*x;
-	if(es==0) 			/* IEEE 754 logb */
-		return -16382.0;
-	else
-		return (long double) (es-0x3fff);
+  int32_t es, lx, ix;
+
+  GET_LDOUBLE_WORDS (es, ix, lx, x);
+  es &= 0x7fff;			/* exponent */
+  if ((es | ix | lx) == 0)
+    return -1.0 / fabs (x);
+  if (es == 0x7fff)
+    return x * x;
+  if (es == 0)			/* IEEE 754 logb */
+    {
+      /* 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 -16382.0 - (long double)(ma);
+    }
+  return (long double) (es - 16383);
 }
+
 weak_alias (__logbl, logbl)