Function bit_reverse

contents/cooley_tukey/code/c/fft.c:58–78

}

void bit_reverse(double complex *X, size_t N) {
    for (size_t i = 0; i < N; ++i) {
        size_t n = i;
        size_t a = i;
        int count = (int)log2((double)N) - 1;

        n >>= 1;
        while (n > 0) {
            a = (a << 1) | (n & 1);
            count--;
            n >>= 1;
        }
        n = (a << count) & (size_t)((1 << (size_t)log2((double)N)) - 1);

        if (n > i) {
            double complex tmp = X[i];
            X[i] = X[n];
            X[n] = tmp;
        }
    }
}

void iterative_cooley_tukey(double complex *X, size_t N) {
    bit_reverse(X, N);