Fix expm1 missing underflows (bug 16353).

Similar to various other bugs in this area, some expm1 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 issue does not apply to the ldbl-* implementations or to those
for x86 / x86_64 long double.  The change to
sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c is one I missed when
previously fixing bug 16354; the bug in that implementation was
previously latent, but the expm1 fixes stopped it being latent and so
required it to be fixed to avoid spurious underflows from cosh.)

Tested for x86_64 and x86.

	[BZ #16353]
	* sysdeps/i386/fpu/s_expm1.S (dbl_min): New object.
	(__expm1): Force underflow exception for arguments with small
	absolute value.
	* sysdeps/i386/fpu/s_expm1f.S (flt_min): New object.
	(__expm1f): Force underflow exception for arguments with small
	absolute value.
	* sysdeps/ieee754/dbl-64/s_expm1.c: Include <float.h>.
	(__expm1): Force underflow exception for arguments with small
	absolute value.
	* sysdeps/ieee754/flt-32/s_expm1f.c: Include <float.h>.
	(__expm1f): Force underflow exception for arguments with small
	absolute value.
	* sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c (__ieee754_cosh):
	Check for small arguments before calling __expm1.
	* math/auto-libm-test-in: Do not mark underflow exceptions as
	possibly missing for bug 16353.
	* math/auto-libm-test-out: Regenerated.

3 files changed, 14 insertions, 1 deletions

diff --git a/sysdeps/ieee754/dbl-64/s_expm1.c b/sysdeps/ieee754/dbl-64/s_expm1.c
index 9c9bb34559..41ef63a786 100644
--- a/sysdeps/ieee754/dbl-64/s_expm1.c
+++ b/sysdeps/ieee754/dbl-64/s_expm1.c
@@ -109,6 +109,7 @@
  */
 
 #include <errno.h>
+#include <float.h>
 #include <math.h>
 #include <math_private.h>
 #define one Q[0]
@@ -194,6 +195,11 @@ __expm1 (double x)
     }
   else if (hx < 0x3c900000)             /* when |x|<2**-54, return x */
     {
+      if (fabs (x) < DBL_MIN)
+	{
+	  double force_underflow = x * x;
+	  math_force_eval (force_underflow);
+	}
       t = huge + x;     /* return x with inexact flags when x!=0 */
       return x - (t - (huge + x));
     }
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c b/sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c
index 84593521cc..fca80b13f9 100644
--- a/sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c
@@ -50,9 +50,10 @@ __ieee754_cosh (double x)
 	if (ix < 0x40360000) {
 	    /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
 		if(ix<0x3fd62e43) {
+		    if (ix<0x3c800000)			/* cosh(tiny) = 1 */
+		      return one;
 		    t = __expm1(fabs(x));
 		    w = one+t;
-		    if (ix<0x3c800000) return w;	/* cosh(tiny) = 1 */
 		    return one+(t*t)/(w+w);
 		}
 
diff --git a/sysdeps/ieee754/flt-32/s_expm1f.c b/sysdeps/ieee754/flt-32/s_expm1f.c
index ca8839fa22..c81b057f24 100644
--- a/sysdeps/ieee754/flt-32/s_expm1f.c
+++ b/sysdeps/ieee754/flt-32/s_expm1f.c
@@ -14,6 +14,7 @@
  */
 
 #include <errno.h>
+#include <float.h>
 #include <math.h>
 #include <math_private.h>
 
@@ -80,6 +81,11 @@ __expm1f(float x)
 	    c  = (hi-x)-lo;
 	}
 	else if(hx < 0x33000000) {	/* when |x|<2**-25, return x */
+	    if (fabsf (x) < FLT_MIN)
+	      {
+		float force_underflow = x * x;
+		math_force_eval (force_underflow);
+	      }
 	    t = huge+x;	/* return x with inexact flags when x!=0 */
 	    return x - (t-(huge+x));
 	}