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Fix tanh missing underflows (bug 16520) [committed]
- From: Joseph Myers <joseph at codesourcery dot com>
- To: <libc-alpha at sourceware dot org>
- Date: Thu, 13 Aug 2015 16:41:24 +0000
- Subject: Fix tanh missing underflows (bug 16520) [committed]
- Authentication-results: sourceware.org; auth=none
Similar to various other bugs in this area, some tanh implementations
do not raise the underflow exception for subnormal arguments, when the
result is tiny and inexact. This patch forces the exception in a
similar way to previous fixes.
Tested for x86_64, x86, mips64 and powerpc. Committed.
(auto-libm-test-out diffs omitted below.)
2015-08-13 Joseph Myers <joseph@codesourcery.com>
[BZ #16520]
* sysdeps/ieee754/dbl-64/s_tanh.c: Include <float.h>.
(__tanh): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/flt-32/s_tanhf.c: Include <float.h>.
(__tanhf): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/ldbl-128/s_tanhl.c: Include <float.h>.
(__tanhl): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/ldbl-128ibm/s_tanhl.c: Include <float.h>.
(__tanhl): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/ldbl-96/s_tanhl.c: Include <float.h>.
(__tanhl): Force underflow exception for arguments with small
absolute value.
* math/auto-libm-test-in: Add more tests of tanh.
* math/auto-libm-test-out: Regenerated.
* sysdeps/i386/fpu/libm-test-ulps: Update.
diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index c32e436..b14146e 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -2779,6 +2779,10 @@ tanh -0x2.6082fp-4
tanh 0xe.05031p-16
tanh 0x3.c80eaa7adaa3p-4
tanh 0x2.00f9857616524p-4
+tanh min
+tanh -min
+tanh min_subnorm
+tanh -min_subnorm
tgamma 0.5
tgamma -0.5
diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index 3603765..de53451 100644
--- a/sysdeps/i386/fpu/libm-test-ulps
+++ b/sysdeps/i386/fpu/libm-test-ulps
@@ -1988,12 +1988,16 @@ ldouble: 4
Function: "tanh_towardzero":
double: 1
float: 1
+idouble: 1
+ifloat: 1
ildouble: 3
ldouble: 3
Function: "tanh_upward":
double: 1
float: 1
+idouble: 1
+ifloat: 1
ildouble: 5
ldouble: 4
diff --git a/sysdeps/ieee754/dbl-64/s_tanh.c b/sysdeps/ieee754/dbl-64/s_tanh.c
index 23cfcde..4f9fcfd 100644
--- a/sysdeps/ieee754/dbl-64/s_tanh.c
+++ b/sysdeps/ieee754/dbl-64/s_tanh.c
@@ -38,6 +38,7 @@ static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";
* only tanh(0)=0 is exact for finite argument.
*/
+#include <float.h>
#include <math.h>
#include <math_private.h>
@@ -68,7 +69,14 @@ __tanh (double x)
if ((ix | lx) == 0)
return x; /* x == +-0 */
if (ix < 0x3c800000) /* |x|<2**-55 */
- return x * (one + x); /* tanh(small) = small */
+ {
+ if (fabs (x) < DBL_MIN)
+ {
+ double force_underflow = x * x;
+ math_force_eval (force_underflow);
+ }
+ return x * (one + x); /* tanh(small) = small */
+ }
if (ix >= 0x3ff00000) /* |x|>=1 */
{
t = __expm1 (two * fabs (x));
diff --git a/sysdeps/ieee754/flt-32/s_tanhf.c b/sysdeps/ieee754/flt-32/s_tanhf.c
index dc96da9..5b48fb2 100644
--- a/sysdeps/ieee754/flt-32/s_tanhf.c
+++ b/sysdeps/ieee754/flt-32/s_tanhf.c
@@ -17,6 +17,7 @@
static char rcsid[] = "$NetBSD: s_tanhf.c,v 1.4 1995/05/10 20:48:24 jtc Exp $";
#endif
+#include <float.h>
#include <math.h>
#include <math_private.h>
@@ -41,7 +42,14 @@ float __tanhf(float x)
if (ix == 0)
return x; /* x == +-0 */
if (ix<0x24000000) /* |x|<2**-55 */
+ {
+ if (fabsf (x) < FLT_MIN)
+ {
+ float force_underflow = x * x;
+ math_force_eval (force_underflow);
+ }
return x*(one+x); /* tanh(small) = small */
+ }
if (ix>=0x3f800000) { /* |x|>=1 */
t = __expm1f(two*fabsf(x));
z = one - two/(t+two);
diff --git a/sysdeps/ieee754/ldbl-128/s_tanhl.c b/sysdeps/ieee754/ldbl-128/s_tanhl.c
index 129735b..8b1706f 100644
--- a/sysdeps/ieee754/ldbl-128/s_tanhl.c
+++ b/sysdeps/ieee754/ldbl-128/s_tanhl.c
@@ -41,6 +41,7 @@
* only tanhl(0)=0 is exact for finite argument.
*/
+#include <float.h>
#include <math.h>
#include <math_private.h>
@@ -73,7 +74,14 @@ __tanhl (long double x)
if (u.value == 0)
return x; /* x == +- 0 */
if (ix < 0x3fc60000) /* |x| < 2^-57 */
- return x * (one + tiny); /* tanh(small) = small */
+ {
+ if (fabsl (x) < LDBL_MIN)
+ {
+ long double force_underflow = x * x;
+ math_force_eval (force_underflow);
+ }
+ return x * (one + tiny); /* tanh(small) = small */
+ }
u.parts32.w0 = ix; /* Absolute value of x. */
if (ix >= 0x3fff0000)
{ /* |x| >= 1 */
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
index fe396e9..5342a8b 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_tanhl.c
@@ -38,6 +38,7 @@ static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";
* only tanh(0)=0 is exact for finite argument.
*/
+#include <float.h>
#include <math.h>
#include <math_private.h>
#include <math_ldbl_opt.h>
@@ -66,7 +67,14 @@ long double __tanhl(long double x)
if (ix == 0)
return x; /* x == +-0 */
if (ix<0x3c60000000000000LL) /* |x|<2**-57 */
+ {
+ if (fabsl (x) < LDBL_MIN)
+ {
+ long double force_underflow = x * x;
+ math_force_eval (force_underflow);
+ }
return x*(one+x); /* tanh(small) = small */
+ }
if (ix>=0x3ff0000000000000LL) { /* |x|>=1 */
t = __expm1l(two*fabsl(x));
z = one - two/(t+two);
diff --git a/sysdeps/ieee754/ldbl-96/s_tanhl.c b/sysdeps/ieee754/ldbl-96/s_tanhl.c
index 7ec6247..035037c 100644
--- a/sysdeps/ieee754/ldbl-96/s_tanhl.c
+++ b/sysdeps/ieee754/ldbl-96/s_tanhl.c
@@ -42,6 +42,7 @@ static char rcsid[] = "$NetBSD: $";
* only tanhl(0)=0 is exact for finite argument.
*/
+#include <float.h>
#include <math.h>
#include <math_private.h>
@@ -69,7 +70,14 @@ long double __tanhl(long double x)
if ((ix|j0|j1) == 0)
return x; /* x == +- 0 */
if (ix<0x3fc8) /* |x|<2**-55 */
+ {
+ if (fabsl (x) < LDBL_MIN)
+ {
+ long double force_underflow = x * x;
+ math_force_eval (force_underflow);
+ }
return x*(one+tiny); /* tanh(small) = small */
+ }
if (ix>=0x3fff) { /* |x|>=1 */
t = __expm1l(two*fabsl(x));
z = one - two/(t+two);
--
Joseph S. Myers
joseph@codesourcery.com