A better Random Number Generator
This is a better random number generator than comes standard. It's from a very good book on algoritms. You should read it
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Source Code
#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;
}
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