hdu 2685 I won't tell you this is about number theory

#include<stdio.h>
#include<string.h>
#define LL __int64

LL mult_mod(LL a,LL b,LL c)
{
a%=c;
b%=c;
LL ret=0;
while(b)
{
if(b&1){ret+=a;ret%=c;}
a<<=1;
if(a>=c)a%=c;
b>>=1;
}
return ret;
}

LL PowerMod(LL a, LL b, LL c)
{

LL ans = 1;
LL k = a % c;
while(b>0) //(k*k % c)2^b %c
{
if(b&1)
ans = mult_mod(ans,k,c);
b = b>>1;
k = mult_mod(k,k,c);
}
return ans;
}

LL gcd(LL a,LL b)
{
if(a==0){return b;}
return gcd(b%a,a);
}
int main()
{
int T;
scanf("%d",&T);
LL a,m,n,k,G;
while(T--)
{
scanf("%I64d%I64d%I64d%I64d",&a,&m,&n,&k);
if(m>n)
{
G = gcd(n,m);
}
else
{
G = gcd(m,n);
}
printf("%I64d\n",(PowerMod(a,G,k)+k-1%k)%k);
}
}

/*
gcd(a^m - 1,a^n - 1) = a^gcd(m,n) - 1

hint:
计算减法的时候 为了保证结果是正数。
a-b % k -> (a%k + k - b%k)%k

*/