标题是我乱起的名字。
在做某题时受到了启发，想出了一种之前没听说过的 MTT，在某谷上一问发现有人和我想的一样，立马去学了。
这种方法，我叫它 128MTT，它用到了科技 __int128。主要思想就是找一个 \(10^{27}\) 以上的大 NTT 模数，全程使用 __int128 做 NTT。
然而 long long 取模尚能用 __int128，__int128 自己又怎么快速模乘呢？解锁新科技：Montgomery 模乘。
这样，我们就可以做一次 NTT 了，吊打各种 \(3\) 次 \(4\) 次的 FFT。（bushi）
这样，我们就可以类 NTT 来做 MTT 了。原理与 NTT 完全相同。
关于 NTT 模数：
for i in range(1000):
if miller_rabin(2**76*i+1): print(i, 2**76*i+1)
58 4382356096103030758309889
60 4533471823554859405148161
93 7026881326510032077979649
100 7555786372591432341913601
145 10955890240257576895774721
151 11409237422613062836289537
235 17756097975589866003496961
286 21609549025611496497872897
288 21760664753063325144711169
348 26294136576618184549859329
352 26596368031521841843535873
385 29089777534477014516367361
441 33321017903128216627838977
442 33396575766854130951258113
466 35209964496276074713317377
502 37930047590408990356406273
531 40121225638460505735561217
547 41330151458075134910267393
582 43974676688482136229937153
603 45561391826726337021739009
651 49188169285570224545857537
795 60068501662101887118213121
813 61428543209168344939757569
832 62864142619960717084721153
835 63090816211138460054978561
841 63544163393493945995493377
861 65055320668012232463876097
972 73442243541588722363400193
988 74651169361203351538106369
993 75028958679832923155202049
其中 Miller-Rabin 是从这里抄来的。
推荐 \(100 \times 2^{76}+1\) 和 \(502 \times 2^{76}+1\)，它们的最小原根都是 \(3\)，且好记。我用的是 \(100 \times 2^{76}+1\).
例题：P4245
#include <iostream>
#include <fstream>
#include <cassert>
#include <algorithm>
#include <vector>
#define UP(i,s,e) for(auto i=s; i!=e; ++i)
using std::cin;
using std::cout;
namespace BITS{ // }{{{
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;
struct u256{
u128 hi, lo;
constexpr u256(u128 hi, u128 lo):hi(hi), lo(lo){}
constexpr u256 &operator=(u256 x){ hi=x.hi, lo=x.lo; return *this; }
constexpr u256 operator+=(u256 x){
if(((lo>>1)+(x.lo>>1)+(lo&1&x.lo)) >> 63) hi++;
hi += x.hi; lo += x.lo;
return *this;
}
};
constexpr u256 mul128(u128 x, u128 y){
u64 xl(x), xh(x>>64), yl(y), yh(y>>64);
u128 mid(u128(xl)*yh), anslo(u128(xl)*yl);
u64 mh(mid>>64), ml(mid);
mid = u128(yl)*xh + ml + (anslo >> 64);
return u256(u128(xh)*yh + mh + (mid>>64),
(mid<<64) | u64(anslo));
}
constexpr u128 str_to_u128(char const *s){
u128 x(0);
while(*s){ x = x*10+(*s)-'0'; s++; }
return x;
}
char* u128_to_string(u128 x){ // u128 < 10**39
char buf[40]={0}, *p = buf+38;
do {
*p = x%10 + '0';
x/=10;
p--;
} while(x>0);
return p+1;
}
} // {}}}
BITS::u64 gethi(BITS::u128 x){ return x>>64; }
BITS::u64 getlo(BITS::u128 x){ return x; }
template<typename T>
constexpr T exgcd(T a, T b, T &x, T &y){
if(b == 0) return x=1, y=0, void();
exgcd(b, a%b, y, x); y-=a/b*x;
}
template<typename T>
constexpr T qpow(T x, BITS::u128 tim){
T a(1);
while(tim){
if(tim&1) a*=x;
x*=x;
tim>>=1;
}
return a;
}
namespace Montgomery{ // }{{{
using namespace BITS;
constexpr u128 MOD = str_to_u128("7555786372591432341913601"); // MOD must be < 2**63
constexpr int MOD_G = 3;
constexpr u128 NIMOD = -qpow(MOD, (u128(1)<<127)-1);
constexpr int lgR = 128;
constexpr u128 reduce(u256 x){
x += mul128(x.lo*NIMOD, MOD); // mod 2**lgR
assert(x.lo == 0);
return x.hi >= MOD ? x.hi-MOD : x.hi;
}
constexpr u128 R1 = reduce(mul128((-MOD)%MOD, (-MOD)%MOD));
constexpr u128 R2_(){
u256 ans = mul128(R1, R1); u128 anslo(ans.lo%MOD);
while(ans.hi > 0){
ans.hi %= MOD;
ans = mul128(ans.hi, R1);
anslo += ans.lo%MOD;
anslo %= MOD;
}
return anslo;
}
constexpr u128 R2 = R2_();
constexpr u128 R3 = reduce(mul128(R2, R2));
constexpr u128 mmul(u128 x, u128 y){ return reduce(mul128(x,y)); }
class m128{ // Montgomery unsigned 128 bit modulo MOD
private:
u128 val;
public:
m128(){}
m128 &operator=(m128 x){ val = x.val; return *this; }
m128 &operator=(u128 x){ val = mmul(x, R2); return *this; }
m128(u128 x){ *this = x; }
m128 &operator+=(m128 x){ val += x.val; val = val>=MOD ? val-MOD :val; return *this; }
m128 operator+(m128 x){ x+=*this; return x; }
m128 &operator-=(m128 x){ if(val < x.val) val+=MOD; val -= x.val; return *this; }
m128 operator-(m128 x){ m128 t=*this; t-=x; return t; }
m128 &operator*=(m128 x){ val = mmul(val, x.val); return *this; }
m128 operator*(m128 x){ x*=*this; return x; }
u128 get(){ return mmul(val, 1); }
};
} // {}}}
namespace Poly{ // }{{{
using CC = Montgomery::m128;
using Montgomery::MOD_G;
using Montgomery::MOD;
void change(CC *y, int len){
static std::vector<int> rev; static int llen = 0;
if(llen != len){
llen = len;
rev.reserve(len);
rev[0] = 0;
UP(i, 1, len){
rev[i] = rev[i>>1] >> 1;
if(i&1) rev[i] |= len>>1;
}
}
UP(i, 0, len) if(i<rev[i]) std::swap(y[i], y[rev[i]]);
}
void ntt(CC *y, int len, bool idft){
change(y, len);
for(int h=2; h<=len; h<<=1){
CC wn = qpow(CC(MOD_G), (MOD-1)/h);
for(int j=0; j<len; j+=h){
CC w(1);
UP(k, j, j+h/2){
CC u = y[k], v = w * y[k+h/2];
y[k] = u+v, y[k+h/2] = u-v;
w = w * wn;
}
}
}
if(idft){
std::reverse(y+1, y+len);
CC invlen = qpow(CC(len), MOD-2);
UP(i, 0, len){
y[i] *= invlen;
}
}
}
void dot(CC *y, CC *z, int len){ UP(i, 0, len) y[i] *= z[i]; }
void polymul(CC *y, CC *z, int len){
ntt(y, len, false);
ntt(z, len, false);
dot(y, z, len);
ntt(y, len, true);
}
} // {}}}
namespace m{ // }{{{
int in, im, ip;
Poly::CC ia[1<<18], ib[1<<18];
void work(){
cin >> in >> im >> ip;
UP(i, 0, in+1){
int x;
cin >> x;
ia[i] = x;
}
UP(i, 0, im+1){
int x;
cin >> x;
ib[i] = x;
}
int len = 1;
while(len < im+in+1) len<<=1;
Poly::polymul(ia, ib, len);
UP(i, 0, in+im+1){
cout << BITS::u64(ia[i].get()%ip) << ' ';
}
}
} // {}}}
int main(){
#if ONLINE_JUDGE
std::ios::sync_with_stdio(0); std::cin.tie(0);
#endif
m::work(); return 0;
}
跑的比这篇慢多了，果然人傻常大 =(
标签：return,val,m128,笔记,学习,constexpr,128MTT,u128,MOD From： https://www.cnblogs.com/x383494/p/17577595.html