Correct IBM long double nextafterl.

Fix for values near a power of two, and some tidies.

	[BZ #16739]
	* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl): Correct
	output when value is near a power of two.  Use int64_t for lx and
	remove casts.  Use decimal rather than hex exponent constants.
	Don't use long double multiplication when double will suffice.
	* math/libm-test.inc (nextafter_test_data): Add tests.
	* NEWS: Add 16739 and 16786 to bug list.

4 files changed, 52 insertions, 17 deletions

diff --git a/ChangeLog b/ChangeLog
index 7c737abaf8..f623e8b79a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2014-04-02  Alan Modra  <amodra@gmail.com>
 
+	[BZ #16739]
+	* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl): Correct
+	output when value is near a power of two.  Use int64_t for lx and
+	remove casts.  Use decimal rather than hex exponent constants.
+	Don't use long double multiplication when double will suffice.
+	* math/libm-test.inc (nextafter_test_data): Add tests.
+	* NEWS: Add 16739 and 16786 to bug list.
+
+2014-04-02  Alan Modra  <amodra@gmail.com>
+
 	* sysdeps/powerpc/powerpc64/power7/memrchr.S: Correct stream hint.
 
 2014-04-02  Alan Modra  <amodra@gmail.com>
diff --git a/NEWS b/NEWS
index 31723768eb..d959fb3377 100644
--- a/NEWS
+++ b/NEWS
@@ -13,7 +13,7 @@ Version 2.20
   16357, 16362, 16447, 16532, 16545, 16574, 16599, 16600, 16609, 16610,
   16611, 16613, 16623, 16632, 16634, 16639, 16642, 16648, 16649, 16670,
   16674, 16677, 16680, 16683, 16689, 16695, 16701, 16706, 16707, 16712,
-  16713, 16714, 16731, 16743, 16758, 16759, 16760, 16770.
+  16713, 16714, 16731, 16739, 16743, 16758, 16759, 16760, 16770, 16786.
 
 * Running the testsuite no longer terminates as soon as a test fails.
   Instead, a file tests.sum (xtests.sum from "make xcheck") is generated,
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 19194f63e9..967b679e94 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -8302,6 +8302,14 @@ static const struct test_ff_f_data nextafter_test_data[] =
     // XXX Enable once gcc is fixed.
     //TEST_ff_f (nextafter, 0x0.00000040000000000000p-16385L, -0.1L, 0x0.0000003ffffffff00000p-16385L),
 #endif
+#if defined TEST_LDOUBLE && LDBL_MANT_DIG == 106
+    TEST_ff_f (nextafter, 1.0L, -10.0L, 1.0L-0x1p-106L, NO_EXCEPTION),
+    TEST_ff_f (nextafter, 1.0L, 10.0L, 1.0L+0x1p-105L, NO_EXCEPTION),
+    TEST_ff_f (nextafter, 1.0L-0x1p-106L, 10.0L, 1.0L, NO_EXCEPTION),
+    TEST_ff_f (nextafter, -1.0L, -10.0L, -1.0L-0x1p-105L, NO_EXCEPTION),
+    TEST_ff_f (nextafter, -1.0L, 10.0L, -1.0L+0x1p-106L, NO_EXCEPTION),
+    TEST_ff_f (nextafter, -1.0L+0x1p-106L, -10.0L, -1.0L, NO_EXCEPTION),
+#endif
 
     /* XXX We need the hexadecimal FP number representation here for further
        tests.  */
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c b/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c
index 30b1540a88..bf57cb89d6 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c
@@ -30,8 +30,7 @@ static char rcsid[] = "$NetBSD: $";
 
 long double __nextafterl(long double x, long double y)
 {
-	int64_t hx,hy,ihx,ihy;
-	uint64_t lx;
+	int64_t hx, hy, ihx, ihy, lx;
 	double xhi, xlo, yhi;
 
 	ldbl_unpack (x, &xhi, &xlo);
@@ -79,19 +78,28 @@ long double __nextafterl(long double x, long double y)
 	      u = math_opt_barrier (x);
 	      x -= __LDBL_DENORM_MIN__;
 	      if (ihx < 0x0360000000000000LL
-		  || (hx > 0 && (int64_t) lx <= 0)
-		  || (hx < 0 && (int64_t) lx > 1)) {
+		  || (hx > 0 && lx <= 0)
+		  || (hx < 0 && lx > 1)) {
 		u = u * u;
 		math_force_eval (u);		/* raise underflow flag */
 	      }
 	      return x;
 	    }
-	    if (ihx < 0x06a0000000000000LL) { /* ulp will denormal */
-	      INSERT_WORDS64 (yhi, hx & (0x7ffLL<<52));
-	      u = yhi;
-	      u *= 0x1.0000000000000p-105L;
+	    /* If the high double is an exact power of two and the low
+	       double is the opposite sign, then 1ulp is one less than
+	       what we might determine from the high double.  Similarly
+	       if X is an exact power of two, and positive, because
+	       making it a little smaller will result in the exponent
+	       decreasing by one and normalisation of the mantissa.   */
+	    if ((hx & 0x000fffffffffffffLL) == 0
+		&& ((lx != 0 && (hx ^ lx) < 0)
+		    || (lx == 0 && hx >= 0)))
+	      ihx -= 1LL << 52;
+	    if (ihx < (106LL << 52)) { /* ulp will denormal */
+	      INSERT_WORDS64 (yhi, ihx & (0x7ffLL<<52));
+	      u = yhi * 0x1p-105;
 	    } else {
-	      INSERT_WORDS64 (yhi, (hx & (0x7ffLL<<52))-(0x069LL<<52));
+	      INSERT_WORDS64 (yhi, (ihx & (0x7ffLL<<52))-(105LL<<52));
 	      u = yhi;
 	    }
 	    return x - u;
@@ -109,8 +117,8 @@ long double __nextafterl(long double x, long double y)
 	      u = math_opt_barrier (x);
 	      x += __LDBL_DENORM_MIN__;
 	      if (ihx < 0x0360000000000000LL
-		  || (hx > 0 && (int64_t) lx < 0 && lx != 0x8000000000000001LL)
-		  || (hx < 0 && (int64_t) lx >= 0)) {
+		  || (hx > 0 && lx < 0 && lx != 0x8000000000000001LL)
+		  || (hx < 0 && lx >= 0)) {
 		u = u * u;
 		math_force_eval (u);		/* raise underflow flag */
 	      }
@@ -118,12 +126,21 @@ long double __nextafterl(long double x, long double y)
 		x = -0.0L;
 	      return x;
 	    }
-	    if (ihx < 0x06a0000000000000LL) { /* ulp will denormal */
-	      INSERT_WORDS64 (yhi, hx & (0x7ffLL<<52));
-	      u = yhi;
-	      u *= 0x1.0000000000000p-105L;
+	    /* If the high double is an exact power of two and the low
+	       double is the opposite sign, then 1ulp is one less than
+	       what we might determine from the high double.  Similarly
+	       if X is an exact power of two, and negative, because
+	       making it a little larger will result in the exponent
+	       decreasing by one and normalisation of the mantissa.   */
+	    if ((hx & 0x000fffffffffffffLL) == 0
+		&& ((lx != 0 && (hx ^ lx) < 0)
+		    || (lx == 0 && hx < 0)))
+	      ihx -= 1LL << 52;
+	    if (ihx < (106LL << 52)) { /* ulp will denormal */
+	      INSERT_WORDS64 (yhi, ihx & (0x7ffLL<<52));
+	      u = yhi * 0x1p-105;
 	    } else {
-	      INSERT_WORDS64 (yhi, (hx & (0x7ffLL<<52))-(0x069LL<<52));
+	      INSERT_WORDS64 (yhi, (ihx & (0x7ffLL<<52))-(105LL<<52));
 	      u = yhi;
 	    }
 	    return x + u;