fix s_mp_montgomery_reduce_fast as proposed by @dmitry-lipetsk This fixes #62
diff --git a/bn_s_mp_montgomery_reduce_fast.c b/bn_s_mp_montgomery_reduce_fast.c
index 843ad12..3f0c672 100644
--- a/bn_s_mp_montgomery_reduce_fast.c
+++ b/bn_s_mp_montgomery_reduce_fast.c
@@ -119,7 +119,7 @@ mp_err s_mp_montgomery_reduce_fast(mp_int *x, const mp_int *n, mp_digit rho)
/* alias for next word, where the carry goes */
_W = W + ++ix;
- for (; ix <= ((n->used * 2) + 1); ix++) {
+ for (; ix < ((n->used * 2) + 1); ix++) {
*_W++ += *_W1++ >> (mp_word)MP_DIGIT_BIT;
}