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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Card game deck but with trumps suit for tarot "divination" Is
 there a better way than enumerating all cards?
Date: Sat, 3 Feb 2018 09:17:41 +0100
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Date: 2018-02-03T09:17:41+01:00
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On 02/03/2018 12:05 AM, Randy Brukardt wrote:
> 
> An alternative approach using current Ada would be to use a fixed
> Discrete_Random range (0 .. 77), and simply discard any values that identify
> cards already dealt, just retrying to get a random value. This works well
> and is properly uniform, but only if you are going to deal part of the deck
> (say 25%). If you need to deal the whole deck, it can get slow toward the
> end when most of the values returned from Random have already been dealt.
> (That's especially bad if you forget to special case the last card to the
> dealt - you don't need a random choice to figure out which one that is after
> all of the rest have been dealt.)
> 
> Experience shows that most users don't get this right, as did the discussion
> on the topic (in which many knowledgeable people suggested approaches which
> just don't work). I had to fix the Janus/Ada random number generator after
> that discussion, as it had made one of the mistakes as well.

The PragmAda Reusable Components have functions to obtain a uniformly 
distributed integer in a range from a uniformly distributed floating-point 
(psuedo-) random value (PragmARC.Real_Random_Ranges.Random_Int), and from a 
uniformly distributed random Unsigned_32 (PragmARC.Random_Ranges). A lot of 
effort went into convincing oneself that these were done correctly. No one has 
reported any problem with them, but no one has said that they are correct, either.

https://github.com/jrcarter/PragmARC

-- 
Jeff Carter
"I spun around, and there I was, face to face with a
six-year-old kid. Well, I just threw my guns down and
walked away. Little bastard shot me in the ass."
Blazing Saddles
40