位示图的实现

1.  定义：

        位示图（bitmap）又叫位图，它的最小单元是一个bit。每个bit有两种取值1或0。

        位示图是一种非常常用的结构，在索引，数据压缩等方面有广泛应用。本文介绍了位图的实现方法及其应用场景。

                          

2. 实现

       在C/C++中没有位示图这种数据类型，下面我们利用int来实现一个位示图类

       每个int有sizeof(int)*8个bit

 

3.代码

  1: #include<cassert>

  2: #include<iostream>

  3: 

  4: using namespace std ;

  5: 

  6: #define INT_BIT sizeof(int)

  7: #define MAX     1024*1024*1024

  8: #define SHIFT   5

  9: #define UNIT    INT_BIT << 3 // INT_BIT * 2^3 

 10: #define MASK    0x1f

 11: 

 12: class BitSet

 13: {

 14:     public :

 15:         BitSet(int maxSize=MAX)

 16:             : _msize(maxSize)

 17:         {

 18:             pBitset = new int[_msize/UNIT+1] ;

 19:         } 

 20: 

 21:         ~BitSet()

 22:         {

 23:             if (pBitset){

 24:                 delete [] pBitset ;

 25:             }

 26:         }

 27: 

 28:         void set(int i) 

 29:         {   

 30:             assert(i<_msize) ;

 31:             // i >> SHIFT = i / (2^5)

 32:             // i & MASK = i % 32

 33:             int j = i ;

 34:             if (j>UNIT){

 35:                 j >>= SHIFT ;

 36:             }

 37:             pBitset[j] |= 1 << (i & MASK) ;

 38:         }

 39: 

 40:         void clear(int i) 

 41:         {

 42:             assert(i<_msize) ;

 43:             int j = i ;

 44:             if (j>UNIT){

 45:                 j >>= SHIFT ;

 46:             }

 47:             pBitset[j] &= ~(1 << (i & MASK)) ;

 48:         }

 49: 

 50:         bool test(int i) 

 51:         {

 52:             assert(i<_msize) ;

 53:             int j = i ;

 54:             if (j>UNIT){

 55:                 j >>= SHIFT ;

 56:             } 

 57:             return (pBitset[j] & (1<< (i & MASK))) ;

 58:         }

 59:     private:

 60:         int _msize ;

 61:         int *pBitset ;

 62: } ;

 63: 

4. 测试代码

  1: int main()

  2: {

  3:     BitSet bitset(100) ;

  4:     int i  = 80 ;

  5:     bitset.set(i) ;

  6:     

  7:     if (bitset.test(i)){

  8:         cout << "the pos " << i << " is seted" << endl ; 

  9:     }else{

 10:         cout << "the pos " << i << " is not seted" << endl ; 

 11:     }

 12:     

 13:     bitset.clear(i) ;

 14: 

 15:     if (bitset.test(i)){

 16:         cout << "the pos " << i << " is seted" << endl ; 

 17:     }else{

 18:         cout << "the pos " << i << " is not seted" << endl ; 

 19:     }

 20: }