tests/tdiv.c: added a test that triggers a bug in mpfr_div in case of

underflow in rounding to nearest when the result must be non-zero.

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@5514 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 24 insertions, 5 deletions

diff --git a/tests/tdiv.c b/tests/tdiv.c
index 6cf099ac9..b9a92f448 100644
--- a/tests/tdiv.c
+++ b/tests/tdiv.c
@@ -626,6 +626,7 @@ check_nan (void)
 {
   mpfr_t  a, d, q;
   mp_exp_t emax, emin;
+  int i;
 
   mpfr_init2 (a, 100L);
   mpfr_init2 (d, 100L);
@@ -718,11 +719,29 @@ check_nan (void)
   set_emin (-1);
   mpfr_set_ui (a, 1, GMP_RNDZ);
   mpfr_div_2exp (a, a, 2, GMP_RNDZ);
-  mpfr_set_ui (d, 2, GMP_RNDZ);
-  test_div (q, a, d, GMP_RNDZ); /* 0.5*2^(-2) -> underflow */
-  MPFR_ASSERTN (mpfr_cmp_ui (q, 0) == 0 && MPFR_IS_POS (q));
-  test_div (q, a, d, GMP_RNDN); /* 0.5*2^(-2) -> underflow */
-  MPFR_ASSERTN (mpfr_cmp_ui (q, 0) == 0 && MPFR_IS_POS (q));
+  mpfr_set_prec (d, mpfr_get_prec (q) + 8);
+  for (i = -1; i <= 1; i++)
+    {
+      /* Test 2^(-2) / (2 + eps), with eps < 0, eps = 0, eps > 0.
+         -> underflow.
+         With div.c r5513, this test fails for eps < 0 in GMP_RNDN. */
+      mpfr_set_ui (d, 2, GMP_RNDZ);
+      if (i < 0)
+        mpfr_nextbelow (d);
+      if (i > 0)
+        mpfr_nextabove (d);
+      mpfr_clear_flags ();
+      test_div (q, a, d, GMP_RNDZ); /* result = 0 */
+      MPFR_ASSERTN (mpfr_underflow_p ());
+      MPFR_ASSERTN (MPFR_IS_ZERO (q) && MPFR_IS_POS (q));
+      mpfr_clear_flags ();
+      test_div (q, a, d, GMP_RNDN); /* result = 0 iff eps >= 0 */
+      MPFR_ASSERTN (mpfr_underflow_p ());
+      MPFR_ASSERTN (MPFR_IS_POS (q));
+      if (i < 0)
+        mpfr_nextbelow (q);
+      MPFR_ASSERTN (MPFR_IS_ZERO (q));
+    }
   set_emin (emin);
 
   mpfr_clear (a);