[li2.c] fixed bug when x is near 0

[tli2.c] added new test


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@6512 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 33 insertions, 0 deletions

diff --git a/li2.c b/li2.c
index 4f0fa54a4..b65d6ab25 100644
--- a/li2.c
+++ b/li2.c
@@ -276,6 +276,8 @@ mpfr_li2 (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
         {
           mpfr_ui_sub (u, 1, x, MPFR_RNDN);
           mpfr_log (u, u, MPFR_RNDU);
+          if (MPFR_IS_ZERO(u))
+            goto next_m;
           mpfr_neg (u, u, MPFR_RNDN);    /* u = -log(1-x) */
           expo_l = MPFR_GET_EXP (u);
           k = li2_series (s, u, MPFR_RNDU);
@@ -292,6 +294,7 @@ mpfr_li2 (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
           if (MPFR_CAN_ROUND (s, (mp_exp_t) m - err, yp, rnd_mode))
             break;
 
+        next_m:
           MPFR_ZIV_NEXT (loop, m);
           mpfr_set_prec (u, m);
           mpfr_set_prec (s, m);
diff --git a/tests/tli2.c b/tests/tli2.c
index cfc159758..f7f7ff4da 100644
--- a/tests/tli2.c
+++ b/tests/tli2.c
@@ -147,11 +147,41 @@ normal (void)
   mpfr_clear (y);
 }
 
+static void
+bug20091013 (void)
+{
+  mpfr_t x, y;
+  int inex;
+
+  mpfr_init2 (x, 17);
+  mpfr_init2 (y, 2);
+  mpfr_set_str_binary (x, "0.10000000000000000E-16");
+  inex = mpfr_li2 (y, x, MPFR_RNDN);
+  if (mpfr_cmp_ui_2exp (y, 1, -17) != 0)
+    {
+      printf ("Error in bug20091013()\n");
+      printf ("expected 2^(-17)\n");
+      printf ("got      ");
+      mpfr_dump (y);
+      exit (1);
+    }
+  if (inex >= 0)
+    {
+      printf ("Error in bug20091013()\n");
+      printf ("expected negative ternary value, got %d\n", inex);
+      exit (1);
+    }
+  mpfr_clear (x);
+  mpfr_clear (y);
+}
+
 int
 main (int argc, char *argv[])
 {
   tests_start_mpfr ();
 
+  bug20091013 ();
+
   special ();
 
   normal ();