public void run() {
                        if (isign > 0) {
                            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;
                            }
                        } else {
                            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;
                            }
                        }
                    }