更高效率的A^B mod C bird

#include <stdio.h>
#define LL unsigned long long int

inline LL mod(LL a,LL b)
{
while (a>=b)
a-=b;
return a;
}
//a*b mod c
inline LL MulAndMod(LL a, LL shl_b,LL c)
{
LL val,pre;
pre = mod(a,c);
val = 0;
while (shl_b)
{
if (shl_b&0x1)
val = mod(val + pre,c);
shl_b>>=1;
pre = mod(pre<<1,c);
}
return val;
}

inline LL A_BModC(LL a,LL shl_b,LL c)
{

LL val,pre;
if (shl_b&0x1) //根据2相应二进制位的值判断是否加A*2^n；\\因为有对b进行右移运算，所以每次只需判断最末位的结果就可以。
val = mod(a,c);
else
val = 1;
shl_b >>= 1; //计算 A*2^n的值。
pre = MulAndMod(a,a,c);
while (shl_b)
{
if (shl_b&0x1)
val = MulAndMod(val,pre,c);
shl_b>>=1;
pre = MulAndMod(pre,pre,c);
}
return val;
}

int main()
{
LL a,b,c;
while (scanf("%llu%llu%llu", &a,&b,&c)!=EOF)
printf("%llu\n", A_BModC(a,b,c));
return 0;
}