[sdiy] Random Number Generation by Lookup table : The Code

[David Hughes]

Folks,

For those who e-mailed asking for the code... here's the browser stuff...

It produces 2K's worth of byte-sized comma-seperated values... (I also loaded
the file into Excell and did a scatter plot to check for randomness... ?:)  )

> <SCRIPT LANGUAGE="Javascript">
> <!-- Hide from non-Javascript browsers
> 
> 	DisplayRandomNumber(2048, 0, 255);
> 
> 
> /**************************************************************************************/
> 
> function DisplayRandomNumber(RandomNumberCount, MinimumNumber, MaximumNumber)
> {
>    while (RandomNumberCount-- > 0)
>       {
>       ThisNumber = RandomNumber(MaximumNumber);
>       document.writeln(ThisNumber, ", ");
>       }
> }
> 
> /**************************************************************************************/
> 
> function RandomNumber(SeedValue)
> {
> var MyNumber = 0;
> 
>    MyNumber = Math.random();
>    MyNumber = Math.round(MyNumber * SeedValue);
>    return MyNumber;
> }
> 
> /**************************************************************************************/
> 
> //-->
> </SCRIPT>

Wrap it in HTML to make it work...



And here's the table look-up code...

Call UpdateRandomNumberIndex() every time an event occurs - especially
asynchronous events - and the behaviour should be pretty random even though it's table-based.



> /*************************************************************************************/
> 
> /* UpdateRandomNumberIndex() is called to reset the index into the random number table.
>    We do this one a regular basis but take the number at the current index position and
>    add it to the index, wrapping back to the start if we hit the top of the table. This
>    should give us completely random behavior.
> */
> 
> void UpdateRandomNumberIndex()
> {
> unsigned char TableEntry;
> 
> 	TableEntry = RandomNumberTable[RandomNumberIndex];
> 	RandomNumberIndex += TableEntry;
> 	if (RandomNumberIndex > _NUMBER_OF_RANDOM_TABLE_ENTRIES)
> 		RandomNumberIndex = RandomNumberIndex - _NUMBER_OF_RANDOM_TABLE_ENTRIES;		
> }
>    
> /*************************************************************************************/
> 
> /* Random() is called to generate a random number in the range of 0..100 inclusive.
> */
> 
> unsigned int Random()
> {
> 	UpdateRandomNumberIndex();
> 	return RandomNumberTable[RandomNumberIndex];
> }
> 
> /*************************************************************************************/
> 
> /* GetRandomNumberInRange() is called to return a random number in the range specified
>    by the calling parameters.
> */
>  
> unsigned int GetRandomNumberInRange(unsigned int MinimumValue, unsigned int MaximumValue)
> {
> unsigned int RandomNumber;
> unsigned int Range;
>    
> 	Range = MaximumValue - MinimumValue + 1;
> 	RandomNumber = Random();
> 	RandomNumber = ((RandomNumber * Range) / _RANDOM_NUMBER_RANGE) + MinimumValue;
>    return RandomNumber;
> }
> 
> /*************************************************************************************/

As you can see, it ain't rocket-science and it's fast...

Regards
   David

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