public void run() {
                        for (int i = firstIdx; i < lastIdx; i++) {
                            int idx1 = 2 * i;
                            int idx2 = idx1 + 1;
                            a[offa + i] = bk1[idx1] * ak[idx1] - bk1[idx2] * ak[idx2];
                        }
                    }