Fixed bug in exp(-eps) for rounding toward zero (test was also wrong).mpfr-2-1-branch

[2.1 branch]


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/branches/mpfr-2-1-branch@3847 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 17 insertions, 2 deletions

diff --git a/exp.c b/exp.c
index 56fbb9ce9..8ed1202f7 100644
--- a/exp.c
+++ b/exp.c
@@ -83,7 +83,8 @@ mpfr_exp (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd_mode)
       int signx = MPFR_SIGN(x);
 
       MPFR_SET_POS(y);
-      if (MPFR_IS_NEG_SIGN(signx) && (rnd_mode == GMP_RNDD))
+      if (MPFR_IS_NEG_SIGN(signx) && (rnd_mode == GMP_RNDD ||
+                                      rnd_mode == GMP_RNDZ))
         {
           mpfr_setmax (y, 0);  /* y = 1 - epsilon */
           return -1;
diff --git a/tests/texp.c b/tests/texp.c
index 44f84d813..8127fb597 100644
--- a/tests/texp.c
+++ b/tests/texp.c
@@ -250,12 +250,16 @@ check_special ()
   if (mpfr_cmp_ui_2exp (y, 3, -2))
     {
       printf ("Error for exp(-1/16), prec=2, RNDD\n");
+      printf ("expected 0.11, got ");
+      mpfr_dump (y);
       exit (1);
     }
   mpfr_exp (y, x, GMP_RNDZ);
-  if (mpfr_cmp_ui (y, 1))
+  if (mpfr_cmp_ui_2exp (y, 3, -2))
     {
       printf ("Error for exp(-1/16), prec=2, RNDZ\n");
+      printf ("expected 0.11, got ");
+      mpfr_dump (y);
       exit (1);
     }
   mpfr_set_str_binary (x, "0.1E-3");
@@ -361,6 +365,16 @@ check_inexact (void)
       mpfr_out_str (stdout, 16, 0, x, GMP_RNDN); putchar ('\n');
     }
 
+  /* bug found by Guillaume Melquiond, 13 Sep 2005 */
+  mpfr_set_prec (x, 53);
+  mpfr_set_str_binary (x, "-1E-400");
+  mpfr_exp (x, x, GMP_RNDZ);
+  if (mpfr_cmp_ui (x, 1) == 0)
+    {
+      printf ("Error for exp(-2^(-400))\n");
+      exit (1);
+    }
+
   mpfr_clear (x);
   mpfr_clear (y);
 }