RE: CEERAN0 not allways random?

["Haas, Matt" <Matt.Haas@xxxxxxxxxxx>]

There are lots of things computers are good for. Being random isn't one of 
them. Since you use the same seed value all the time, you're going to end up 
with the same "random" number sequences. Most "random number generators" 
(including CEERAN0) generate what are called pseudo random numbers. The 
sequence is predictable using the same input values so you're actually seeing 
the expected behavior. A little bit of searching on Google turned this up which 
explains it better than I care to: http://triumvir.org/articles/rng/

Basically, what it gets down to is that you need to introduce some randomness 
(which is difficult since computers aren't very random) to generate better 
"random" numbers. Things like time and other stuff that changes frequently 
(network information, system activity levels, etc...) are generally used to 
seed random number generators to give better randomness. Feeding the random 
number back in as the seed value is an example of doing this. The article I 
reference above shows a better (as in more "random") way to do the same thing.

You never said what the purpose of the random number was but if you just need a 
unique number, you can generate a UUID (Universally Unique ID -- these are 
supposed to be unique on all computers as opposed to a GUID [Globally Unique 
ID] which is only supposed to be unique on a given computer). Here's an example 
of doing that:

D UUID_template   DS
D  UtBytPrv                     10u 0 Inz( %Size( UUID_template ))
D  UtBytAvl                     10u 0
D                                8a   Inz( *Allx'00' )
D  UUID                         16a

D GenUuid         PR                  ExtProc('_GENUUID')
D  UUID_template                  *   Value

C                   Callp     GenUuid( %Addr( UUID_template ))

In this example, the result is stored in UUID which is character but since a 
UUID is a 128 bit integer you should be able to convert it to numeric with no 
problem. You could also convert it to a character representation of it's hex 
value (it will be 32 characters then) which is usually how you see them used 
since you probably will have unprintable characters in it's raw form as 
returned from the API.

Matt

-----Original Message-----
From: Titus Kruse [mailto:t_kruse@xxxxxxxxx]
Sent: Friday, April 30, 2004 8:18 AM
To: RPG programming on the AS400 / iSeries
Subject: Re: CEERAN0 not allways random?


> 
>  /Free
>   Seed = 0;
>   for c = 1 to 20000;
>     CEERAN0(Seed:Random:*OMIT);
>     Seed = Random * 1234 * c;
>     Number = %DecH(Random:30:29) * seed * 9999 ;
>     except;
>   endfor;

Hmm, why do you take the random number for the new seed? Here my coding:

>   Seed = 0;
>   for c = 1 to 20000;
>     CEERAN0(Seed:Random:*OMIT);
>     Number = %Dec(Random) * 10 ** 16;
>   except;
>   endfor;



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