random number generator.txt

一个随机数发生器的代码

//************************************** 
    // Name: A better Random Number Generator 
    // Description:This is a better random number generator 
    // than comes standard. It's from a very good book on 
    // algoritms. You should read it 
    // By: Andy Williams 
    // 
    // 
    // Inputs:None 
    // 
    // Returns:None 
    // 
    //Assumes:None 
    // 
    //Side Effects:None 
    // 
    //************************************** 
    
    #include <iostream.h> 
    #include <time.h> 

    void init_mm( ); 
    int number_range( int from, int to ); 
    int number_mm( void ); 

    static      int     rgiState[2+55]; // leave this alone     
    
    void main() 
    { 
        init_mm(); //seed the number generator 
        int random = number_range( 10, 100 ); 
        cout << random << endl; 
    } 
    
    int number_mm( void ) 
    { 
    int *piState; 
    int iState1; 
    int iState2; 
    int iRand; 
    piState             = &rgiState[2]; 
    iState1             = piState[-2]; 
    iState2             = piState[-1]; 
    iRand               = ( piState[iState1] + piState[iState2] ) 
                        & ( ( 1 << 30 ) - 1 ); 
    piState[iState1]    = iRand; 
    if ( ++iState1 == 55 ) 
        iState1 = 0; 
    if ( ++iState2 == 55 ) 
        iState2 = 0; 
    piState[-2]         = iState1; 
    piState[-1]         = iState2; 
    return iRand >> 6; 
    } 
    
    /* 
    * Generate a random number. 
    */ 
    int number_range( int from, int to ) 
    { 
    int power; 
    int number; 
    if ( ( to = to - from + 1 ) <= 1 ) 
        return from; 
    for ( power = 2; power < to; power <<= 1 ) 
        ; 
    while ( ( number = number_mm( ) & ( power - 1 ) ) >= to ) 
        ; 
    return from + number; 
    } 
    
    /* 
    * This is the Mitchell-Moore algorithm from Knuth Volume II. 
    */ 

    void init_mm( ) 
    { 
    int *piState; 
    int iState; 
    piState     = &rgiState[2]; 
    piState[-2] = 55 - 55; 
    piState[-1] = 55 - 24; 
    piState[0]  = ( (int) time( NULL ) ) & ( ( 1 << 30 ) - 1 ); 
    piState[1]  = 1; 
    for ( iState = 2; iState < 55; iState++ ) 
    { 
        piState[iState] = ( piState[iState-1] + piState[iState-2] ) 
                        & ( ( 1 << 30 ) - 1 ); 
    } 
    return; 
    }