public void run() {
                        for (int i = firstIdx; i < lastIdx; i++) {
                            int idx1 = 2 * i;
                            int idx2 = idx1 + 1;
                            float im = ak[idx1] * bk2[idx2] + ak[idx2] * bk2[idx1];
                            ak[idx1] = ak[idx1] * bk2[idx1] - ak[idx2] * bk2[idx2];
                            ak[idx2] = im;
                        }
                    }