int n = __builtin_ctz(f.size());

int N = f.size();

for (int i = 0; i < n; ++i) {

for (int j = 0; j < N; ++j) {

if (!(j & (1 << i))) f[j ^ (1 << i)] += f[j];

}

}

int n = __builtin_ctz(f.size());

int N = f.size();

for (int i = 0; i < n; ++i) {

for (int j = 0; j < N; ++j) {

if (!(j & (1 << i))) f[j ^ (1 << i)] -= f[j];

}

continue;

}

int N = a.size();

vector<T> c(N);

for (int i = 0; i < N; ++i) {

for (int j = i; j < N; j = (j + 1) | i) {

c[j] += a[i] * b[i ^ j];

}

}

return c;

int N = a.size();

int n = __builtin_ctz(N);

// Stupid is faster when n < 16

if (n < 16) return stupid_convolution(a, b);

vector<vector<T> > fa(n + 1, vector<T>(N));

vector<vector<T> > fb(n + 1, vector<T>(N));

vector<vector<T> > fc(n + 1, vector<T>(N));

for (int i = 0; i < N; ++i) {

fa[__builtin_popcount(i)][i] = a[i];

fb[__builtin_popcount(i)][i] = b[i];

}

for (int i = 0; i <= n; ++i) {

mobius(fa[i]);

mobius(fb[i]);

}

for (int i = 0; i <= n; ++i) {

for (int j = 0; j + i <= n; ++j) {

for (int k = 0; k < N; ++k) {

fc[i + j][k] += fa[i][k] * fb[j][k];

}

}

}

for (int i = 0; i <= n; ++i) {

inverse_mobius(fc[i]);

}

vector<T> c(N);

for (int i = 0; i < N; ++i) {

c[i] = fc[__builtin_popcount(i)][i];

}

return c;