POJ Fibonacii （矩阵快速幂）

#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
struct matrix{
int a[2][2];
}ans,base;
const int MOD = 1e4;
matrix multiply(matrix x, matrix y)
{
matrix tmp;
for (int i = 0; i < 2; i++)
for (int j = 0; j < 2; j++)
{
tmp.a[i][j] = 0;
for (int k = 0; k < 2; k++)
tmp.a[i][j] = (tmp.a[i][j] + x.a[i][k] * y.a[k][j]) % MOD;
}
return tmp;
}
int fast_mod(int n)
{
while (n)
{
if (n & 1) ans = multiply(ans, base);
base = multiply(base, base);
n >>= 1;
}
return ans.a[0][1];
}
int main()
{
int n;
while (scanf("%d", &n) && n != -1)
{
ans.a[0][0] = 1; ans.a[0][1] = 0; ans.a[1][0] = 0; ans.a[1][1] = 1; // 初始化ans为单位矩阵，单位矩阵乘以任何矩阵等于那个矩阵本身
base.a[0][0] = 1; base.a[0][1] = 1; base.a[1][0] = 1; base.a[1][1] = 0;
printf("%d\n", fast_mod(n));
}
return 0;
}