指针优化并没有什么卵用，反而增大了代码的不可读性。

除了本来的循环顺序优化寻址，在预处理单位复数根时，可以连续存储，以增快寻址速度，细节见代码。

代码给出的是FFT，NTT是一样的。

#include
    
     #define fo(i, x, y) for(int i = x, B = y; i <= B; i ++)#define ff(i, x, y) for(int i = x, B = y; i <  B; i ++)#define fd(i, x, y) for(int i = x, B = y; i >= B; i --)#define ll long long#define db double#define pp printf#define hh pp("\n")using namespace std;struct P {    db x, y;    P(db _x = 0, db _y = 0) { x = _x, y = _y;}};P operator + (P a, P b) { return P(a.x + b.x, a.y + b.y);}P operator - (P a, P b) { return P(a.x - b.x, a.y - b.y);}P operator * (P a, P b) { return P(a.x * b.x - a.y * b.y, a.x * b.y + a.y * b.x);}const db pi = acos(-1);const int nm = 1 << 21;int r[nm]; P a[nm], b[nm], W[nm];void dft(P *a, int n, int f) {    ff(i, 0, n) {        r[i] = r[i / 2] / 2 + (i & 1) * (n / 2);        if(i < r[i]) swap(a[i], a[r[i]]);    } P b;    for(int i = 1; i < n; i *= 2) for(int j = 0; j < n; j += 2 * i)        ff(k, 0, i) b = W[i + k] * a[i + j + k], a[i + j + k] = a[j + k] - b, a[j + k] = a[j + k] + b;    if(f == -1) {        reverse(a + 1, a + n);        ff(i, 0, n) a[i].x /= n;    }}void fft(P *a, P *b, int n) {    dft(a, n, 1); dft(b, n, 1);    ff(i, 0, n) a[i] = a[i] * b[i];    dft(a, n, -1);}int main() {    for(int i = 1; i < nm; i *= 2) ff(j, 0, i)        W[i + j] = P(cos(pi * j / i), sin(pi * j / i));    ff(i, 0, 1 << 20) a[i].x = b[i].x = i;    fft(a, b, 1 << 21);}