Fix tanh missing underflows (bug 16520).

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.

	[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.

6 files changed, 46 insertions, 2 deletions

diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index 36037655f2..de53451879 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 23cfcdead5..4f9fcfd2bd 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 dc96da9a5b..5b48fb2e00 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 129735b1b5..8b1706fcdc 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 fe396e9bd3..5342a8b19a 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 7ec6247315..035037c8c7 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);