Fix nextafter overflow in non-default rounding modes (bug 16677).

ISO C requires the result of nextafter to be independent of the
rounding mode, even when underflow or overflow occurs.  This patch
fixes the bug in various nextafter implementations that, having done
an overflowing computation to force an overflow exception (correct),
they then return the result of that computation rather than an
infinity computed some other way (incorrect, when the overflowing
result of arithmetic with that sign and rounding mode is finite but
the correct result is infinite) - generally by falling through to
existing code to return a value that in fact is correct for this case
(but was computed by an integer increment and so without generating
the exceptions required).  Having fixed the bug, the previously
deferred conversion of nextafter testing in libm-test.inc to
ALL_RM_TEST is also included.

Tested x86_64 and x86; also spot-checked results of nextafter tests
for powerpc32 and mips64 to test the ldbl-128ibm and ldbl-128
changes.  (The m68k change is untested.)

	[BZ #16677]
	* math/s_nextafter.c (__nextafter): Do not return value from
	overflowing computation.
	* sysdeps/i386/fpu/s_nextafterl.c (__nextafterl): Likewise.
	* sysdeps/ieee754/flt-32/s_nextafterf.c (__nextafterf): Likewise.
	* sysdeps/ieee754/ldbl-128/s_nextafterl.c (__nextafterl):
	Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl):
	Likewise.
	* sysdeps/m68k/m680x0/fpu/s_nextafterl.c (__nextafterl): Likewise.
	* math/libm-test.inc (nextafter_test): Use ALL_RM_TEST.

9 files changed, 42 insertions, 20 deletions

diff --git a/ChangeLog b/ChangeLog
index 3a589d8b4a..ca74dc312b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2014-03-11  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #16677]
+	* math/s_nextafter.c (__nextafter): Do not return value from
+	overflowing computation.
+	* sysdeps/i386/fpu/s_nextafterl.c (__nextafterl): Likewise.
+	* sysdeps/ieee754/flt-32/s_nextafterf.c (__nextafterf): Likewise.
+	* sysdeps/ieee754/ldbl-128/s_nextafterl.c (__nextafterl):
+	Likewise.
+	* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl):
+	Likewise.
+	* sysdeps/m68k/m680x0/fpu/s_nextafterl.c (__nextafterl): Likewise.
+	* math/libm-test.inc (nextafter_test): Use ALL_RM_TEST.
+
 2014-03-11  Roland McGrath  <roland@hack.frob.com>
 
 	* sysdeps/arm/setjmp.S: Use sfi_breg on stores of mangled registers.
diff --git a/NEWS b/NEWS
index df126f3d3b..51ccb27f5f 100644
--- a/NEWS
+++ b/NEWS
@@ -10,7 +10,7 @@ Version 2.20
 * The following bugs are resolved with this release:
 
   15347, 15804, 15894, 16447, 16532, 16545, 16574, 16600, 16609, 16610,
-  16611, 16613, 16623, 16632, 16639, 16670, 16674, 16683.
+  16611, 16613, 16623, 16632, 16639, 16670, 16674, 16677, 16683.
 
 * The am33 port, which had not worked for several years, has been removed
   from ports.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 0fe0f69e63..574654e222 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -9553,10 +9553,7 @@ static const struct test_ff_f_data nextafter_test_data[] =
 static void
 nextafter_test (void)
 {
-
-  START (nextafter, 1);
-  RUN_TEST_LOOP_ff_f (nextafter, nextafter_test_data, );
-  END;
+  ALL_RM_TEST (nextafter, 1, nextafter_test_data, RUN_TEST_LOOP_ff_f, END);
 }
 
 
diff --git a/math/s_nextafter.c b/math/s_nextafter.c
index 7b026f00ce..28962e52a7 100644
--- a/math/s_nextafter.c
+++ b/math/s_nextafter.c
@@ -70,10 +70,8 @@ double __nextafter(double x, double y)
 	}
 	hy = hx&0x7ff00000;
 	if(hy>=0x7ff00000) {
-	  x = x+x;	/* overflow  */
-	  if (FLT_EVAL_METHOD != 0 && FLT_EVAL_METHOD != 1)
-	    asm ("" : "+m"(x));
-	  return x;	/* overflow  */
+	  double u = x+x;	/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00100000) {
 	    double u = x*x;			/* underflow */
diff --git a/sysdeps/i386/fpu/s_nextafterl.c b/sysdeps/i386/fpu/s_nextafterl.c
index bafe7437fa..66d903f801 100644
--- a/sysdeps/i386/fpu/s_nextafterl.c
+++ b/sysdeps/i386/fpu/s_nextafterl.c
@@ -106,7 +106,10 @@ long double __nextafterl(long double x, long double y)
 	    }
 	}
 	esy = esx&0x7fff;
-	if(esy==0x7fff) return x+x;	/* overflow  */
+	if(esy==0x7fff) {
+	    long double u = x + x;	/* overflow  */
+	    math_force_eval (u);
+	}
 	if(esy==0) {
 	    long double u = x*x;		/* underflow */
 	    math_force_eval (u);		/* raise underflow flag */
diff --git a/sysdeps/ieee754/flt-32/s_nextafterf.c b/sysdeps/ieee754/flt-32/s_nextafterf.c
index b0de3d9ce2..22e0b3d4ed 100644
--- a/sysdeps/ieee754/flt-32/s_nextafterf.c
+++ b/sysdeps/ieee754/flt-32/s_nextafterf.c
@@ -57,10 +57,8 @@ float __nextafterf(float x, float y)
 	}
 	hy = hx&0x7f800000;
 	if(hy>=0x7f800000) {
-	  x = x+x;	/* overflow  */
-	  if (FLT_EVAL_METHOD != 0)
-	    asm ("" : "+m"(x));
-	  return x;	/* overflow  */
+	  float u = x+x;	/* overflow  */
+	  math_force_eval (u);
 	}
 	if(hy<0x00800000) {
 	    float u = x*x;			/* underflow */
diff --git a/sysdeps/ieee754/ldbl-128/s_nextafterl.c b/sysdeps/ieee754/ldbl-128/s_nextafterl.c
index e345bc8c40..d5eaa1cc91 100644
--- a/sysdeps/ieee754/ldbl-128/s_nextafterl.c
+++ b/sysdeps/ieee754/ldbl-128/s_nextafterl.c
@@ -67,7 +67,10 @@ long double __nextafterl(long double x, long double y)
 	    }
 	}
 	hy = hx&0x7fff000000000000LL;
-	if(hy==0x7fff000000000000LL) return x+x;/* overflow  */
+	if(hy==0x7fff000000000000LL) {
+	    long double u = x + x;		/* overflow  */
+	    math_force_eval (u);
+	}
 	if(hy==0) {
 	    long double u = x*x;		/* underflow */
 	    math_force_eval (u);		/* raise underflow flag */
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c b/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c
index c050944c0c..30b1540a88 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c
@@ -66,8 +66,11 @@ long double __nextafterl(long double x, long double y)
 	       long double with a 106 bit mantissa, and nextafterl
 	       is insane with variable precision.  So to make
 	       nextafterl sane we assume 106 bit precision.  */
-	    if((hx==0xffefffffffffffffLL)&&(lx==0xfc8ffffffffffffeLL))
-	      return x+x;	/* overflow, return -inf */
+	    if((hx==0xffefffffffffffffLL)&&(lx==0xfc8ffffffffffffeLL)) {
+	      u = x+x;	/* overflow, return -inf */
+	      math_force_eval (u);
+	      return y;
+	    }
 	    if (hx >= 0x7ff0000000000000LL) {
 	      u = 0x1.fffffffffffff7ffffffffffff8p+1023L;
 	      return u;
@@ -93,8 +96,11 @@ long double __nextafterl(long double x, long double y)
 	    }
 	    return x - u;
 	} else {				/* x < y, x += ulp */
-	    if((hx==0x7fefffffffffffffLL)&&(lx==0x7c8ffffffffffffeLL))
-	      return x+x;	/* overflow, return +inf */
+	    if((hx==0x7fefffffffffffffLL)&&(lx==0x7c8ffffffffffffeLL)) {
+	      u = x+x;	/* overflow, return +inf */
+	      math_force_eval (u);
+	      return y;
+	    }
 	    if ((uint64_t) hx >= 0xfff0000000000000ULL) {
 	      u = -0x1.fffffffffffff7ffffffffffff8p+1023L;
 	      return u;
diff --git a/sysdeps/m68k/m680x0/fpu/s_nextafterl.c b/sysdeps/m68k/m680x0/fpu/s_nextafterl.c
index 03c136bb08..ad77ca4f67 100644
--- a/sysdeps/m68k/m680x0/fpu/s_nextafterl.c
+++ b/sysdeps/m68k/m680x0/fpu/s_nextafterl.c
@@ -89,7 +89,10 @@ long double __nextafterl(long double x, long double y)
 	    }
 	}
 	esy = esx&0x7fff;
-	if(esy==0x7fff) return x+x;	/* overflow  */
+	if(esy==0x7fff) {
+	    long double u = x + x;	/* overflow  */
+	    math_force_eval (u);
+	}
 	if(esy==0 && (hx & 0x80000000) == 0) { /* underflow */
 	    y = x*x;
 	    math_force_eval (y);		/* raise underflow flag */