csu 1556: Jerry's trouble（大数取模）

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
#include<stdlib.h>
#include<algorithm>
#include<queue>
#include<stack>
#include<ctype.h>
#define LL long long
using namespace std;
const LL mod=1e9+7;
LL bitlen(LL x)
{
    LL d=0;
    while(x>0)
    {
        x>>=1;
        d++;
    }
    return d;
}
LL bitat(LL x,LL i)
{
    return (x&(1<<(i-1)));
}
LL module(LL a,LL b,LL n)
{
    LL i,y=1;
    for(int i=bitlen(b);i>0;i--)
    {
        y=(y*y)%n;
        if(bitat(b,i)>0)
            y=(y*a)%n;
    }
    return y;
}
int main()
{
    LL n,m;
    while(scanf("%lld %lld",&n,&m)!=EOF)
    {
        LL ans=0;
        for(LL i=1;i<=n;i++)
        {
            ans+=module(i,m,mod);
        }
        ans=ans%mod;
        printf("%lld\n",ans);
    }
    return 0;
}