diff --git a/al_bool_matrix.hpp b/al_bool_matrix.hpp
index 84f5761..2bf063f 100644
--- a/al_bool_matrix.hpp
+++ b/al_bool_matrix.hpp
@@ -86,11 +86,13 @@ class BoolSquareMatrix {
             STORAGE vector_value = 0;
             for (STORAGE ind = 0; ind < SIZE; ++ind) {
                 BoolVector<STORAGE, SIZE> cur_vec = vec * get_row(ind);
-                STORAGE cur_sum = 0;
+                /* STORAGE cur_sum = 0;
                 for (STORAGE vec_ind = 0; vec_ind < SIZE; ++vec_ind)
                     cur_sum += cur_vec.at(vec_ind);
+                same but slow version, we just need number of bits
+                */
                 vector_value *= 2;
-                vector_value += cur_sum % 2;
+                vector_value += __builtin_popcount(cur_vec.get_value()) % 2; // cur_sum
             }
             return BoolVector<STORAGE, SIZE>(vector_value);
         }