[tests/tcan_round.c] fixed test for small value of GMP_NUMB_BITS

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@13171 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 8 insertions, 1 deletions

diff --git a/tests/tcan_round.c b/tests/tcan_round.c
index a514d2aca..4a046b1f7 100644
--- a/tests/tcan_round.c
+++ b/tests/tcan_round.c
@@ -212,6 +212,7 @@ check_can_round (void)
   int i, u[3] = { 0, 1, 256 };
   int inex;
   int expected, got;
+  int maxerr;
 
   mpfr_inits2 (4 * GMP_NUMB_BITS, x, xinf, xsup, yinf, ysup, (mpfr_ptr) 0);
 
@@ -239,10 +240,16 @@ check_can_round (void)
                 }
               MPFR_ASSERTN (mpfr_get_exp (x) == precx);
 
-              for (err = precy; err <= precy + 3; err++)
+              maxerr = precy + 3;
+              if (4 * GMP_NUMB_BITS < maxerr)
+                maxerr = 4 * GMP_NUMB_BITS;
+              for (err = precy; err <= maxerr; err++)
                 {
                   mpfr_set_ui_2exp (xinf, 1, precx - err, MPFR_RNDN);
                   inex = mpfr_add (xsup, x, xinf, MPFR_RNDN);
+                  /* Since EXP(x) = precx, and xinf = 2^(precx-err),
+                     x + xinf is exactly representable on 4 * GMP_NUMB_BITS
+                     nbits as long as err <= 4 * GMP_NUMB_BITS */
                   MPFR_ASSERTN (inex == 0);
                   inex = mpfr_sub (xinf, x, xinf, MPFR_RNDN);
                   MPFR_ASSERTN (inex == 0);