《编程珠玑》备忘录（开篇）---当每个整数多次出现时

#define INTBITS 4
#define MAXMUM 10
#define BITS (MAXMUM*INTBITS-1)/CHAR_BIT+1   

char arr[BITS];

#define SHIFT 1     //log_2(CHAR_BIT/INTBITS) = 1
#define MASK 0x1    //截取最后一位

void incBit(char *bit, int i)
{
    bit[ i>>SHIFT ] += 1<< ((i&MASK)*INTBITS );
}

#include <iostream>

#define INTBITS 4
#define SHIFT 1
#define MASK 0x1
#define MASK2 0xf
#define MAXMUM 10
#define BITS (MAXMUM*INTBITS-1)/CHAR_BIT+1

using namespace std;

//用于统计整数i出现的频数
void incBit(char *bit, int i)
{
    bit[ i>>SHIFT ] += 1<<( ( i & MASK ) * INTBITS );
}

//用于提取统计结果
int compareBit(char *bit, int i)
{
    return ( bit[ i>>SHIFT ] >> ( ( i&MASK ) * INTBITS ) & MASK2 );
}

int main()
{
    char arr[BITS];
    int test[8] = { 8, 1, 4, 5, 8, 5, 7, 4};

    for(int i=0; i<BITS; i++){
        arr[i] = 0;
    }

    for(int i=0; i<8; i++){
        incBit(arr, test[i]);
    }

    for(int i=0; i<MAXMUM; i++){
        int countNum = compareBit(arr, i);
        if(countNum>0){
            cout<<i<<"; "<<countNum<<endl;
        }
    }

    return 0;
}