public void run() {
                        if (isign > 0) {
                            for (int i = firstIdx; i < lastIdx; i++) {
                                int idx1 = 2 * i;
                                int idx2 = idx1 + 1;
                                a[offa + idx1] = bk1[idx1] * ak[idx1] - bk1[idx2] * ak[idx2];
                                a[offa + idx2] = bk1[idx2] * ak[idx1] + bk1[idx1] * ak[idx2];
                            }
                        } else {
                            for (int i = firstIdx; i < lastIdx; i++) {
                                int idx1 = 2 * i;
                                int idx2 = idx1 + 1;
                                a[offa + idx1] = bk1[idx1] * ak[idx1] + bk1[idx2] * ak[idx2];
                                a[offa + idx2] = -bk1[idx2] * ak[idx1] + bk1[idx1] * ak[idx2];
                            }
                        }
                    }