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Date: Fri, 11 Dec 2020 10:24:01 -0800 (PST)
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Subject: Re: advent of code day 11
From: John Perry <john.perry@usm.edu>
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On Friday, December 11, 2020 at 11:08:00 AM UTC-6, Stephen Leake wrote:
> mildly interesting; variation on Conway's Game of Life. 

I recognized that, too. A solution should not be hard to parallelize, and I'd like to, but for now I have other tasks. (no pun intended, well, OK yes it was)

Here's a couple of questions for the Ada experts. For each round I used two charts, a source and a result. These are arrays, defined like so:

   type Status is ( Floor, Empty, Occupied );

   type Chart_Array is array( Positive range <> , Positive range <> ) of Status;

   Chart1, Chart2: Chart_Array; -- actually defined with appropriate dimensions

A procedure named `Iterate_Seating` applies the given rules to a Chart_Array; an `if` statement determines which iterates into the other.

I thought it would be clearer to use references to switch from one chart to the other, but I had trouble doing that last night. Now I can get it this way:

   Source: Chart_Array renames Chart1;
   Result: Chart_Array renames Chart2;

   while Changed loop

      Perform_Round( Source => Source , Result => Result , ... );
      declare Tmp: Chart_Array renames Source;
      begin
         Source := Result;
         Result := Tmp;
      end;

   end loop;

Does this technique swap references, or does it copy the arrays element-by-element? The run times are the same even if I compel a copy operation; I suppose it's because the arrays aren't large enough, and there aren't enough copies, to make a difference.

thanks
john perry