Fix log1p missing underflows (bug 16339).

Similar to various other bugs in this area, some log1p 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.  (The ldbl-128ibm implementation
doesn't currently need any change as it already generates this
exception, albeit through code that would generate spurious exceptions
in other cases; special code for this issue will only be needed there
when fixing the spurious exceptions.)

Tested for x86_64, x86, powerpc and mips64.

	[BZ #16339]
	* sysdeps/i386/fpu/s_log1p.S (dbl_min): New object.
	(__log1p): Force underflow exception for results with small
	absolute value.
	* sysdeps/i386/fpu/s_log1pf.S (flt_min): New object.
	(__log1pf): Force underflow exception for results with small
	absolute value.
	* sysdeps/ieee754/dbl-64/s_log1p.c: Include <float.h>.
	(__log1p): Force underflow exception for results with small
	absolute value.
	* sysdeps/ieee754/flt-32/s_log1pf.c: Include <float.h>.
	(__log1pf): Force underflow exception for results with small
	absolute value.
	* sysdeps/ieee754/ldbl-128/s_log1pl.c: Include <float.h>.
	(__log1pl): Force underflow exception for results with small
	absolute value.
	* math/auto-libm-test-in: Do not allow missing underflow
	exceptions from log1p.
	* math/auto-libm-test-out: Regenerated.

3 files changed, 23 insertions, 1 deletions

diff --git a/sysdeps/ieee754/dbl-64/s_log1p.c b/sysdeps/ieee754/dbl-64/s_log1p.c
index 86bbfbacaf..cff555b0aa 100644
--- a/sysdeps/ieee754/dbl-64/s_log1p.c
+++ b/sysdeps/ieee754/dbl-64/s_log1p.c
@@ -78,6 +78,7 @@
  *	 See HP-15C Advanced Functions Handbook, p.193.
  */
 
+#include <float.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -118,7 +119,14 @@ __log1p (double x)
 	{
 	  math_force_eval (two54 + x);          /* raise inexact */
 	  if (ax < 0x3c900000)                  /* |x| < 2**-54 */
-	    return x;
+	    {
+	      if (fabs (x) < DBL_MIN)
+		{
+		  double force_underflow = x * x;
+		  math_force_eval (force_underflow);
+		}
+	      return x;
+	    }
 	  else
 	    return x - x * x * 0.5;
 	}
diff --git a/sysdeps/ieee754/flt-32/s_log1pf.c b/sysdeps/ieee754/flt-32/s_log1pf.c
index 94c33fca16..83a09f1414 100644
--- a/sysdeps/ieee754/flt-32/s_log1pf.c
+++ b/sysdeps/ieee754/flt-32/s_log1pf.c
@@ -13,6 +13,7 @@
  * ====================================================
  */
 
+#include <float.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -48,7 +49,14 @@ __log1pf(float x)
 	    if(ax<0x31000000) {			/* |x| < 2**-29 */
 		math_force_eval(two25+x);	/* raise inexact */
 		if (ax<0x24800000)		/* |x| < 2**-54 */
+		  {
+		    if (fabsf (x) < FLT_MIN)
+		      {
+			float force_underflow = x * x;
+			math_force_eval (force_underflow);
+		      }
 		    return x;
+		  }
 		else
 		    return x - x*x*(float)0.5;
 	    }
diff --git a/sysdeps/ieee754/ldbl-128/s_log1pl.c b/sysdeps/ieee754/ldbl-128/s_log1pl.c
index b70a55b758..ff759bc000 100644
--- a/sysdeps/ieee754/ldbl-128/s_log1pl.c
+++ b/sysdeps/ieee754/ldbl-128/s_log1pl.c
@@ -53,6 +53,7 @@
     <http://www.gnu.org/licenses/>.  */
 
 
+#include <float.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -140,6 +141,11 @@ __log1pl (long double xm1)
 
   if ((hx & 0x7fffffff) < 0x3f8e0000)
     {
+      if (fabsl (xm1) < LDBL_MIN)
+	{
+	  long double force_underflow = xm1 * xm1;
+	  math_force_eval (force_underflow);
+	}
       if ((int) xm1 == 0)
 	return xm1;
     }