[src/zeta.c] Added a FIXME: bug in the error computation due to the

  use of the native double C type, which can yield an overflow.
[tests/tzeta.c] Added a corresponding test case, which gives an
  assertion failure.

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@10865 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/tzeta.c b/tests/tzeta.c
index 6bb292d1c..f1ad4138a 100644
--- a/tests/tzeta.c
+++ b/tests/tzeta.c
@@ -240,6 +240,7 @@ main (int argc, char *argv[])
   mpfr_t s, y, z;
   mpfr_prec_t prec;
   mpfr_rnd_t rnd_mode;
+  mpfr_flags_t flags;
   int inex;
 
   tests_start_mpfr ();
@@ -453,6 +454,24 @@ main (int argc, char *argv[])
         }
     }
 
+  /* The following test yields an overflow in the error computation.
+     With r10864, this is detected and one gets an assertion failure. */
+  mpfr_set_prec (s, 1025);
+  mpfr_set_si_2exp (s, -1, 1024, MPFR_RNDN);
+  mpfr_nextbelow (s);  /* -(2^1024 + 1) */
+  mpfr_clear_flags ();
+  inex = mpfr_zeta (z, s, MPFR_RNDN);
+  flags = __gmpfr_flags;
+  if (flags != (MPFR_FLAGS_OVERFLOW | MPFR_FLAGS_INEXACT) ||
+      ! mpfr_inf_p (z) || MPFR_IS_POS (z) || inex >= 0)
+    {
+      printf ("Error in mpfr_zeta for s = -(2^1024 + 1)\nGot ");
+      mpfr_dump (z);
+      printf ("with inex = %d and flags =", inex);
+      flags_out (flags);
+      exit (1);
+    }
+
   mpfr_clear (s);
   mpfr_clear (y);
   mpfr_clear (z);