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.

diff --git a/ChangeLog b/ChangeLog
index 3a589d8b4a4b2b3a9ccd8755ff0ed1c811a04619..ca74dc312bb2bed385539496b8314479427a655b 100644 (file)
--- 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 df126f3d3bb0f2df25898afd765c80cac3b30536..51ccb27f5f2b66c1ee6d4b94b82ac70a92d6934f 100644 (file)
--- 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 0fe0f69e635c0f32d65751cf8d33876b330e3aed..574654e22258b3dab1a5ec5e04f56f54476cd195 100644 (file)
--- 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 7b026f00cee976fea2da0d21f5ff1b1cfe3818a2..28962e52a7e45ca6a61820392b3cfca3b6e7091a 100644 (file)
--- 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 bafe7437fac2638d70d70f098f04bd1aea451b59..66d903f80198b2076171c234b5d978b675751e9e 100644 (file)
--- 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 b0de3d9ce2a90a6d69ccc514338a70bf933d6578..22e0b3d4ed4231a3f2c2226b7fdab1a5b74a5c7f 100644 (file)
--- 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 e345bc8c40d625dfe42517f1e9dd5c87ed2e6aca..d5eaa1cc912eeea952ff647f85d9ebf25bc3425a 100644 (file)
--- 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 c050944c0c270134fcd5b73d8f0eb8709fbad249..30b1540a8849a4c9d9b07b852b22950fb4faec49 100644 (file)
--- 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 03c136bb085623391f9b335371eed81f1a92a598..ad77ca4f676bf17318ec3f7a15cf6cf5daaab9fe 100644 (file)
--- 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 */