Re: [question] On the topic of randomness.

[Bob Pendleton <bobp@pendleton.com>]

Laguna Loire wrote:
> 
> Thanks for the response, Tim! :)
> 
> 
> In anycase, with the bag of marbles, I had wondered about how one could
> alter the level of randomness instead of leaving it up to chance, as it
> were. ^_^;;

Let's say you have a bag of red and blue marbles. If there are 10 red
marbles and 90 blue marbles the odds of drawing a red marble is 10% and
a blue is 90%. If you have an array with 100 elements in it, and 10 or
those elements are 0 and 90 are 1 and you use a random integer in the
range of 0 to 99 (assuming 0 based arrays as in C) to select an entry at
random you will find that 10% of the time you get 0 and 90% of the time
you get 1. There is your bag of marbles. Whether you get a 0 (red) or a
1 (blue) is a matter of chance but on average you will see 9 blues for
each red you see.

				Bob P.

> 
> Wing.

Here is a simple fast good random number generator

#ifndef _FRAND_H_
#define _FRAND_H_

//---------------------------------------------------
/*

    An inline replacement for srand() and rand()
    it returns a number between 0 and 0xffff.

    The original code was found in "Graphic Gems II"
*/
//---------------------------------------------------

extern long _FRSEED_;

#define FRAND_MAX (0xffffl)

#define fsrand(seed)    (_FRSEED_ = seed)

#define frand()     ((_FRSEED_ = (((25173l * _FRSEED_) + 13849l))) &
0xffffl)


//---------------------------------------------------

#endif
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