BZ #15536: Fix ulp for 128-bit IBM long double.

In 128-bit IBM long double the precision of the type
decreases as you approach subnormal numbers, equaling
that of a double for subnormal numbers. Therefore
adjust the computation in ulp to use 2^(MIN_EXP - MANT_DIG)
which is correct for FP_SUBNORMAL for all types.

3 files changed, 35 insertions, 12 deletions

diff --git a/ChangeLog b/ChangeLog
index 5f2e4c61eb..91a183ad84 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2013-06-03  Carlos O'Donell  <carlos@redhat.com>
+
+	[BZ #15536]
+	* math/libm-test.inc (MAX_EXP): Remove
+	(MIN_EXP): Define.
+	(ulp): Use MIN_EXP - MANT_DIG.
+	(check_ulp): Verify subnormal ulps. Only allow a range of +/- 1 ulp.
+
 2013-05-31  Carlos O'Donell  <carlos@redhat.com>
 
 	* po/be.po: Revert last change.
diff --git a/NEWS b/NEWS
index acfc19c1bd..9452cc1959 100644
--- a/NEWS
+++ b/NEWS
@@ -19,7 +19,7 @@ Version 2.18
   15337, 15339, 15342, 15346, 15359, 15361, 15366, 15380, 15381, 15394,
   15395, 15405, 15406, 15409, 15416, 15418, 15419, 15423, 15424, 15426,
   15429, 15441, 15442, 15448, 15465, 15480, 15485, 15488, 15490, 15493,
-  15497, 15506, 15529, 15553.
+  15497, 15506, 15529, 15536, 15553.
 
 * CVE-2013-0242 Buffer overrun in regexp matcher has been fixed (Bugzilla
   #15078).
diff --git a/math/libm-test.inc b/math/libm-test.inc
index 7a6bf09a66..6870d96d5b 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -269,8 +269,8 @@ static FLOAT max_error, real_max_error, imag_max_error;
 
 #define MANT_DIG CHOOSE ((LDBL_MANT_DIG-1), (DBL_MANT_DIG-1), (FLT_MANT_DIG-1),  \
 			 (LDBL_MANT_DIG-1), (DBL_MANT_DIG-1), (FLT_MANT_DIG-1))
-#define MAX_EXP CHOOSE ((LDBL_MAX_EXP-1), (DBL_MAX_EXP-1), (FLT_MAX_EXP-1),	\
-			(LDBL_MAX_EXP-1), (DBL_MAX_EXP-1), (FLT_MAX_EXP-1))
+#define MIN_EXP CHOOSE ((LDBL_MIN_EXP-1), (DBL_MIN_EXP-1), (FLT_MIN_EXP-1),	\
+			(LDBL_MIN_EXP-1), (DBL_MIN_EXP-1), (FLT_MIN_EXP-1))
 
 /* Compare KEY (a string, with the name of a test or a function) with
    ULP (a pointer to a struct ulp_data structure), returning a value
@@ -680,7 +680,7 @@ ulp (FLOAT value)
 	/* Fall through...  */
       case FP_SUBNORMAL:
         /* The next closest subnormal value is a constant distance away.  */
-	ulp = FUNC(ldexp) (1.0, 1 - (MAX_EXP + MANT_DIG));
+	ulp = FUNC(ldexp) (1.0, MIN_EXP - MANT_DIG);
 	break;
 
       case FP_NORMAL:
@@ -14583,7 +14583,7 @@ parse_opt (int key, char *arg, struct argp_state *state)
 void
 check_ulp (void)
 {
-   FLOAT ulps, value;
+   FLOAT ulps, ulpx, value;
    int i;
    /* Check ulp of zero is a subnormal value...  */
    ulps = ulp (0x0.0p0);
@@ -14599,30 +14599,45 @@ check_ulp (void)
        fprintf (stderr, "ulp (1.0L) is not FP_NORMAL\n");
        exit (EXIT_FAILURE);
      }
+
+   /* Compute the next subnormal value using nextafter to validate ulp.
+      We allow +/- 1 ulp around the represented value.  */
+   value = FUNC(nextafter) (0, 1);
+   ulps = ULPDIFF (value, 0);
+   ulpx = ulp (1.0L);
+   if (ulps < (1.0L - ulpx) || ulps > (1.0L + ulpx))
+     {
+       fprintf (stderr, "Value outside of 1 +/- 1ulp.\n");
+       exit (EXIT_FAILURE);
+     }
    /* Compute the nearest representable number from 10 towards 20.
-      The result is 10 + 1ulp.  We use this to check the ulp function.  */
+      The result is 10 + 1ulp.  We use this to check the ulp function.
+      We allow +/- 1 ulp around the represented value.  */
    value = FUNC(nextafter) (10, 20);
    ulps = ULPDIFF (value, 10);
-   if (ulps > 1.0L)
+   ulpx = ulp (1.0L);
+   if (ulps < (1.0L - ulpx) || ulps > (1.0L + ulpx))
      {
-       fprintf (stderr, "The value of ulp (10+1ulp,10) is greater than 1 ulp.\n");
+       fprintf (stderr, "Value outside of 1 +/- 1ulp.\n");
        exit (EXIT_FAILURE);
      }
    /* This gives one more ulp.  */
    value = FUNC(nextafter) (value, 20);
    ulps = ULPDIFF (value, 10);
-   if (ulps > 2.0L)
+   ulpx = ulp (2.0L);
+   if (ulps < (2.0L - ulpx) || ulps > (2.0L + ulpx))
      {
-       fprintf (stderr, "The value of ulp (10+2ulp,10) is greater than 2 ulp.\n");
+       fprintf (stderr, "Value outside of 2 +/- 1ulp.\n");
        exit (EXIT_FAILURE);
      }
    /* And now calculate 100 ulp.  */
    for (i = 2; i < 100; i++)
      value = FUNC(nextafter) (value, 20);
    ulps = ULPDIFF (value, 10);
-   if (ulps > 100.0L)
+   ulpx = ulp (100.0L);
+   if (ulps < (100.0L - ulpx) || ulps > (100.0L + ulpx))
      {
-       fprintf (stderr, "The value of ulp (10+100ulp,10) is greater than 100 ulp.\n");
+       fprintf (stderr, "Value outside of 100 +/- 1ulp.\n");
        exit (EXIT_FAILURE);
      }
 }