fixed SEGV (mpn_lshift doesn't seem to like src_size=0)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@743 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 4 insertions, 1 deletions

diff --git a/sub.c b/sub.c
index 1e8542ba7..14b16c55b 100644
--- a/sub.c
+++ b/sub.c
@@ -272,7 +272,10 @@ mpfr_sub1(a, b, c, rnd_mode, diff_exp)
 	    mpn_lshift(ap, cp+(cn-an), an, overlap);
 	    ap[0] += cp[cn-an-1]>>(BITS_PER_MP_LIMB-overlap);
 	  }
-	  else mpn_lshift(ap+(an-cn), cp, cn, overlap);
+	  else {
+	    /* warning: mpn_lshift doesn't seem to like cn=0 */
+	    if (cn) mpn_lshift(ap+(an-cn), cp, cn, overlap); 
+	  }
 	}
 	else MPN_COPY(ap+(an-cn), cp, cn);
       }