Using Hash table to achieve rapid index buffer

enum {
    kHashBits   = 8, 
    kHashCount  = 1 << kHashBits, //Hash表大小(1<<8=256)，值越大缓存检索越快
};

struct data_t{
    unsigned int id; //必须是唯一值，ID不能为0
    char * data_ptr;
};

static data_t * hash_cache[kHashCount]={0};

//Hash值生成函数
unsigned int hash_fun(unsigned int id)
{
    id ^= id >> 16;
    id ^= id >> 8;
    return id%kHashCount;
}

data_t * find_by_hash_cache(unsigned int id)
{
    unsigned int hid=hash_fun(id);

    data_t *p=hash_cache[hid]; //从Hash表缓冲查找
    if (p->id==id)
    {
        return p;
    }

    p=find_by_list(id); //从链表或者其他数据结构查找
    if (p)
    {
        hash_cache[hid]=p; //存入Hash表
        return p;
    }

    return NULL;
}