[tests/tmul.c] added underflow test for directed rounding too

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@10602 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 39 insertions, 5 deletions

diff --git a/tests/tmul.c b/tests/tmul.c
index 1556a0029..c5472c466 100644
--- a/tests/tmul.c
+++ b/tests/tmul.c
@@ -632,7 +632,7 @@ test_underflow (mpfr_prec_t pmax)
   mpfr_t a, b, c;
   int inex;
 
-  /* we want b*c < 0.5*2^emin but round(b*c, p) >= 0.5*2^emin thus
+  /* for RNDN, we want b*c < 0.5*2^emin but round(b*c, p) = 0.5*2^emin thus
      b*c >= (0.5 - 1/4*ulp_p(0.5))*2^emin */
   for (p = MPFR_PREC_MIN; p <= pmax; p++)
     {
@@ -646,15 +646,49 @@ test_underflow (mpfr_prec_t pmax)
       /* 0.5 - 1/4*ulp_p(0.5) <= b * c < 0.5 */
       mpfr_mul_2si (b, b, mpfr_get_emin () / 2, MPFR_RNDZ);
       mpfr_mul_2si (c, c, (mpfr_get_emin () - 1) / 2, MPFR_RNDZ);
-      if (inex)
-        mpfr_nextabove (c);
       mpfr_set_prec (a, p);
       mpfr_clear_underflow ();
       mpfr_mul (a, b, c, MPFR_RNDN);
       if (!mpfr_zero_p (a) && mpfr_underflow_p ())
         {
-          printf ("Error, underflow flag incorrectly set for emin=%ld\n",
-                  mpfr_get_emin ());
+          printf ("Error, underflow flag incorrectly set for emin=%ld, rnd=%s\n",
+                  mpfr_get_emin (), mpfr_print_rnd_mode (MPFR_RNDN));
+          printf ("b="); mpfr_dump (b);
+          printf ("c="); mpfr_dump (c);
+          printf ("a="); mpfr_dump (a);
+          mpfr_set_prec (a, mpfr_get_prec (b) + mpfr_get_prec (c));
+          mpfr_mul_2exp (b, b, 1, MPFR_RNDN);
+          mpfr_mul (a, b, c, MPFR_RNDN);
+          printf ("2*a="); mpfr_dump (a);
+          exit (1);
+        }
+      mpfr_clear (a);
+      mpfr_clear (b);
+      mpfr_clear (c);
+    }
+
+  /* for RNDU, we want b*c < 0.5*2^emin but round(b*c, p) = 0.5*2^emin thus
+     b*c > (0.5 - 1/2*ulp_p(0.5))*2^emin */
+  for (p = MPFR_PREC_MIN; p <= pmax; p++)
+    {
+      mpfr_init2 (a, p);
+      mpfr_init2 (b, p + 10);
+      mpfr_init2 (c, p + 10);
+      mpfr_urandomb (b, RANDS);
+      mpfr_set_ui_2exp (a, 1, -1, MPFR_RNDZ); /* a = 0.5 */
+      mpfr_nextbelow (a); /* 0.5 - 1/2*ulp_p(0.5) */
+      inex = mpfr_div (c, a, b, MPFR_RNDU);
+      /* 0.5 - 1/2*ulp_p(0.5) <= b * c < 0.5 */
+      mpfr_mul_2si (b, b, mpfr_get_emin () / 2, MPFR_RNDZ);
+      mpfr_mul_2si (c, c, (mpfr_get_emin () - 1) / 2, MPFR_RNDZ);
+      if (inex)
+        mpfr_nextabove (c); /* ensures that b*c > (0.5 - 1/2*ulp_p(0.5))*2^emin */
+      mpfr_clear_underflow ();
+      mpfr_mul (a, b, c, MPFR_RNDN);
+      if (!mpfr_zero_p (a) && mpfr_underflow_p ())
+        {
+          printf ("Error, underflow flag incorrectly set for emin=%ld, rnd=%s\n",
+                  mpfr_get_emin (), mpfr_print_rnd_mode (MPFR_RNDU));
           printf ("b="); mpfr_dump (b);
           printf ("c="); mpfr_dump (c);
           printf ("a="); mpfr_dump (a);