/*
 * call-seq:
 *     digest_obj.hexdigest -> string
 *     digest_obj.hexdigest(string) -> string
 *
 * If none is given, returns the resulting hash value of the digest in
 * a hex-encoded form, keeping the digest's state.
 *
 * If a _string_ is given, returns the hash value for the given
 * _string_ in a hex-encoded form, resetting the digest to the initial
 * state before and after the process.
 */
static VALUE
rb_digest_instance_hexdigest(int argc, VALUE *argv, VALUE self)
{
    VALUE str, value;

    if (rb_scan_args(argc, argv, "01", &str) > 0) {
        rb_funcall(self, id_reset, 0);
        rb_funcall(self, id_update, 1, str);
        value = rb_funcall(self, id_finish, 0);
        rb_funcall(self, id_reset, 0);
    } else {
        VALUE clone = rb_obj_clone(self);

        value = rb_funcall(clone, id_finish, 0);
        rb_funcall(clone, id_reset, 0);
    }

    return hexencode_str_new(value);
}