[src/div.c] Bug fix: avoid integer overflow in the code added in r9086

(now tdiv no longer fails).

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@9107 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 7 insertions, 1 deletions

diff --git a/src/div.c b/src/div.c
index 5a26a7cf8..bc1d4c8ec 100644
--- a/src/div.c
+++ b/src/div.c
@@ -366,7 +366,13 @@ mpfr_div (mpfr_ptr q, mpfr_srcptr u, mpfr_srcptr v, mpfr_rnd_t rnd_mode)
           MPFR_CHANGE_SIGN(q);
         }
       /* q did not under/overflow */
-      MPFR_EXP(q) -= exp_v - GMP_NUMB_BITS;
+      MPFR_EXP(q) -= exp_v;
+      /* The following test is needed, otherwise the next addition
+         on the exponent may overflow, e.g. when dividing the
+         largest finite MPFR number by the smallest positive one. */
+      if (MPFR_UNLIKELY (MPFR_EXP(q) > __gmpfr_emax - GMP_NUMB_BITS))
+        return mpfr_overflow (q, rnd_mode, MPFR_SIGN(q));
+      MPFR_EXP(q) += GMP_NUMB_BITS;
       return mpfr_check_range (q, inex, rnd_mode);
     }