随機數一

#include <iostream>

 #include <map>

 using namespace std ;

 #include <time.h>

 #include <math.h>


 //C語言的庫函數rand有以下兩個可改進之處

 //範圍太小，才3萬多，改成40億多

 //需要srand，如果不srand 預設隻是1。CRand預設值是clock()。注意：Windows下GetTickCount更精确


 #define ULONG unsigned long

 //接口

 class IRand

 {

 public:

     //不實作SetSeed防止多次SetSeed引起種子值相同。構造函數中初始化種子

     virtual ULONG Rand()=0;

 };




 class CRand : public IRand

 {

 public:

     CRand(ULONG s1 = clock(),ULONG s2 = time(NULL) )

     {

         m_iSeed1 = s1 ;

         m_iSeed2 = s2 ;

     }

     

     ULONG Rand()

     {

         ULONG b;

     

         b = m_iSeed1 ^ (m_iSeed1 >> 2) ^ (m_iSeed1 >> 6) ^ (m_iSeed1 >> 7);

         m_iSeed1 = (m_iSeed1 >> 1) | (~b << 31);


         b = (m_iSeed2 << 1) ^ (m_iSeed2 << 2) ^ (m_iSeed1 << 3) ^ (m_iSeed2 << 4);

         m_iSeed2 = (m_iSeed2 << 1) | (~b >> 31);


         return m_iSeed1 ^ m_iSeed2;

     }

 protected:

     ULONG m_iSeed1;

     ULONG m_iSeed2;

 };



 void main()

 {

     const int n = 100;

     CRand r ;

     

     for( int i = 0 ; i < n ; i++ )

     {

         cout << r.Rand() << endl ;

     }

 }