added 1 to the precision of x to allow an exact difference v-w

in the Karatsuba code


git-svn-id: svn://scm.gforge.inria.fr/svn/mpc/trunk@12 211d60ee-9f03-0410-a15a-8952a2c7a4e4

1 files changed, 2 insertions, 1 deletions

diff --git a/mul.c b/mul.c
index 99f989f..4161f1f 100644
--- a/mul.c
+++ b/mul.c
@@ -283,7 +283,8 @@ mpc_mul_karatsuba (mpc_ptr rop, mpc_srcptr op1, mpc_srcptr op2, mpc_rnd_t rnd)
 	     mp_prec_t prec_x;
 	     prec_x = (MPFR_EXP(v) > MPFR_EXP(w)) ? MPFR_EXP(v) - MPFR_EXP(w)
 	       : MPFR_EXP(w) - MPFR_EXP(v);
-	     prec_x += (prec_v > prec_w) ? prec_v : prec_w;
+	     prec_x += MAX(prec_v, prec_w) + 1;
+           /* +1 is necessary for a potential carry */
 	     /* ensure we do not use a too large precision */
 	     if (prec_x > prec_u)
 	       prec_x = prec_u;