fixed bug reg. negative and zero input

Author: czurnieden

bn_mp_to_radix.c

@@ -31,6 +31,9 @@ mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, i
    if (MP_IS_ZERO(a)) {
       *str++ = '0';
       *str = '\0';
+      if (written != NULL) {
+         *written = 2u;
+      }
       return MP_OKAY;
    }
 
@@ -72,8 +75,9 @@ mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, i
 
    /* append a NULL so the string is properly terminated */
    *str = '\0';
+   digs++;
    if (written != NULL) {
-      *written = digs + 1;
+      *written = (a->sign == MP_NEG) ? digs + 1u: digs;
    }
 
 LBL_ERR: