| 35 | } |
| 36 | |
| 37 | void cooley_tukey(double complex *X, const size_t N) { |
| 38 | if (N >= 2) { |
| 39 | double complex tmp [N / 2]; |
| 40 | for (size_t i = 0; i < N / 2; ++i) { |
| 41 | tmp[i] = X[2*i + 1]; |
| 42 | X[i] = X[2*i]; |
| 43 | } |
| 44 | for (size_t i = 0; i < N / 2; ++i) { |
| 45 | X[i + N / 2] = tmp[i]; |
| 46 | } |
| 47 | |
| 48 | cooley_tukey(X, N / 2); |
| 49 | cooley_tukey(X + N / 2, N / 2); |
| 50 | |
| 51 | for (size_t i = 0; i < N / 2; ++i) { |
| 52 | X[i + N / 2] = X[i] - cexp(-2.0 * I * M_PI * (double)i / (double)N) * X[i + N / 2]; |
| 53 | X[i] -= (X[i + N / 2]-X[i]); |
| 54 | } |
| 55 | } |
| 56 | } |
| 57 | |
| 58 | void bit_reverse(double complex *X, size_t N) { |
| 59 | for (size_t i = 0; i < N; ++i) { |