bitset实现

　　最近看到C++的bitset，突然好奇他们是怎么实现的。对内存的管理不可避免要用到指针，可是指针是用类型的，对bit的管理用什么指针效率高呢？于是就自己尝试写了个用char*来管理内存的bitset，当然自己这个效率稳健都无法于源码相比，所以命名成BitMap，只当是练习了。不过经过我的测试，发现这种方法的效率并不比c++的bitset效率低。　　

　　主要代码如下(Download)：

#include <iostream>
#include <malloc.h>
using namespace std;

/*
 *This class implemented BitMap with the memory management using char* type
 *it provide three public functions:
 *
 *getBit(unsigned long index) get the bit value in position index
 *
 *setBit(unsigned long index, bool value) set the bit value in position index
 *
 *printBitMap() print the bits
 *
 */
class BitMap{
        public:
                bool getBit(unsigned long index);
                void setBit(unsigned long index,bool value);
                void printBitMap();

        /*
         * the construction and destruction 
         */
        public:
                typedef unsigned char u_char;
                BitMap(unsigned long length);
                ~BitMap();

        private:
                unsigned long buf_size;
                u_char *buf;
                inline u_char _set1(u_char data,int number){
                        return data|0x1<<number;
                }
                inline u_char _set0(u_char data,int number){
                        return data&~(0x1<<number);
                }
                inline bool _getbit(u_char data,int number){
                        return (data>>number)&0x1;
                }
                inline void _printChar(u_char data){
                        char buf[9];
                        int i=7;
                        while(i>=0){
                                buf[i--]=(data%2==0 ? '0' : '1');
                                data/=2;
                        }   
                        buf[8]=0;
                        printf("%s",buf);
                }
};

BitMap::BitMap(unsigned long length){
        int tmp=0;
        if((tmp=length%8)!=0)
                buf_size=length+8-tmp;
        else
                buf_size=length;
        buf=(u_char*)malloc(sizeof(sizeof(char)*(buf_size/8)));
};

BitMap::~BitMap(){
        free(this->buf);
};

void BitMap::setBit(unsigned long index,bool isHit){
        if(index>buf_size)
                return ;
        int sub_index=7-index%8;
        u_char *location=buf+index/8;
        if(isHit)
                *location=_set1(*location,sub_index);
        else
                *location=_set0(*location,sub_index);
};

bool BitMap::getBit(unsigned long index){
        return _getbit(*(buf+index/8),7-index%8);
}

void BitMap::printBitMap(){
        u_char *start=buf;
        while(start<=buf+buf_size/8){
                _printChar(*start);
                start++;
        }
        printf("\n");

}

int main(int argc, char **argv){
        BitMap bi(32);
        cout<<"initailize the bitmap"<<endl;
        bi.printBitMap();

        cout<<"set the first bit to 1"<<endl;
        bi.setBit(1,true);
        bi.printBitMap();

        cout<<"set the twenty bit to 1"<<endl;
        bi.setBit(20,true);
        bi.printBitMap();

        bool tp=bi.getBit(20);
        cout<<"is the twenty bit 1? "<< tp<<endl;

}

　　网上搜索到bitset.h的源码，不过一下子被作者神乎其技的coding功夫吓呆了，没看懂。http://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-4.2/bitset-source.html