fixed problem for large negative input

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@4216 280ebfd0-de03-0410-8827-d642c229c3f4

2 files changed, 12 insertions, 7 deletions

diff --git a/erfc.c b/erfc.c
index 65a5983b0..0a01e3420 100644
--- a/erfc.c
+++ b/erfc.c
@@ -70,12 +70,12 @@ mpfr_erfc (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd)
         }
     }
 
-  /* for x < 0, erfc(x) tends to 2 by below */
   if (MPFR_SIGN (x) < 0)
     {
-      if ((MPFR_PREC(y) <= 8 && mpfr_cmp_si (x, -2)) ||
-          (MPFR_PREC(y) <= 26 && mpfr_cmp_si (x, -4)) ||
-          (MPFR_PREC(y) <= 97 && mpfr_cmp_si (x, -9)))
+      /* for x < 0 going to -infinity, erfc(x) tends to 2 by below */
+      if ((MPFR_PREC(y) <= 7 && mpfr_cmp_si (x, -2) <= 0) ||
+          (MPFR_PREC(y) <= 25 && mpfr_cmp_si (x, -4) <= 0) ||
+          (MPFR_PREC(y) <= 120 && mpfr_cmp_si (x, -9)))
         {
           mpfr_set_ui (y, 2, GMP_RNDN);
           mpfr_set_inexflag ();
@@ -91,6 +91,12 @@ mpfr_erfc (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd)
 
   /* Init stuff */
   MPFR_SAVE_EXPO_MARK (expo);
+
+  /* erfc(x) ~ 1, with error < 2^(EXP(x)+1) */
+  MPFR_FAST_COMPUTE_IF_SMALL_INPUT (y, __gmpfr_one, 0-MPFR_GET_EXP (x)-1,
+				    MPFR_SIGN(x) < 0,
+                                    rnd, inex = _inexact; goto end);
+
   prec = MPFR_PREC (y) + MPFR_INT_CEIL_LOG2 (MPFR_PREC (y)) + 3;
   mpfr_init2 (tmp, prec);
 
@@ -118,6 +124,7 @@ mpfr_erfc (mpfr_ptr y, mpfr_srcptr x, mp_rnd_t rnd)
   inex = mpfr_set (y, tmp, rnd);    /* Set y to the computed value */
   mpfr_clear (tmp);
 
+ end:
   MPFR_SAVE_EXPO_FREE (expo);
   return mpfr_check_range (y, inex, rnd);
 }
diff --git a/tests/terf.c b/tests/terf.c
index 6bceed4e6..544a9499a 100644
--- a/tests/terf.c
+++ b/tests/terf.c
@@ -400,9 +400,7 @@ main (int argc, char *argv[])
 
   special_erf ();
   special_erfc ();
-
-  if (argc > 1)
-    large_arg ();
+  large_arg ();
 
   test_generic_erf (2, 100, 15);
   test_generic_erfc (2, 100, 15);