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From: "Jeffrey R. Carter" <spam.jrcarter.not@nospam.acm.org>
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Subject: Re: Randomness tests
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Gautier write-only wrote:
> Does someone have some randomness checking sources in Ada ?
> I am evaluating a fast random generator (published long time ago in
> the Ada letters), alternative to GNAT's implementation.
> Probably the most obvious test is to check that it is well uniformly
> distributed.

An interesting test is the "parking-lot" test. Consecutive pairs of numbers from 
the generator are treated as (x, y) pairs of coordinates and plotted on a graph. 
Poor generators create line segments; good ones don't. (The test gets its name 
from the 1st generator it was applied to, which created short, parallel, 
diagonal line segments that reminded people of the lines in a parking lot.) 
Apparently even generators that do well on other tests can fail this one. The 
generator in Turbo Pascal did especially poorly on this test.

I know of one application in which consecutive triples of numbers were treated 
as (x, y, z) 3-D coordinates. A generator which did well on other tests, 
including the 2-D parking lot test, failed the 3-D version.

Also note that the PragmAda reusable components include the "universal" random 
number generator, which is supposed to be a very good generator, is portable, 
and gives identical results on all platforms.

-- 
Jeff Carter
"Sheriff murdered, crops burned, stores looted,
people stampeded, and cattle raped."
Blazing Saddles
35