From 37d83a089ddf7649ea0a97d4121883381e23f999 Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Thu, 13 Aug 2015 16:40:39 +0000
Subject: 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.
---
 sysdeps/ieee754/dbl-64/s_tanh.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

(limited to 'sysdeps/ieee754/dbl-64')

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));
-- 
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