From: James Edward Gray II <james@...>
Date: 2006-12-22T04:19:40+09:00
Subject: Re: [SUMMARY] Chess960 (#106)

On Dec 21, 2006, at 9:24 AM, Morton Goldberg wrote:

> On Dec 21, 2006, at 8:37 AM, Ruby Quiz wrote:
>
>> Here's the main algorithm from Morton's code (with a minor fix  
>> from me):
>>
>> 	   # ...
>> 	
>> 	   def initialize(number)
>> 	      q, @bishop_index = number.divmod 16
>> 	      @knight_index, @queen_index = q.divmod 6
>> 	      @white_pieces = BISHOP_TABLE[@bishop_index].split('')
>> 	      @white_pieces[nth_dash(@queen_index)] = 'Q'
>> 	      knights = N5N_TABLE[@knight_index]
>> 	      m = knights.index('N')
>> 	      n = knights.index('N', m + 1)
>> 	      m, n = nth_dash(m), nth_dash(n)
>> 	      @white_pieces[m] = 'N'
>> 	      @white_pieces[n] = 'N'
>> 	      @white_pieces[@white_pieces.index('-')] = 'R'
>> 	      @white_pieces[@white_pieces.index('-')] = 'K'
>> 	      @white_pieces[@white_pieces.index('-')] = 'R'
>> 	   end
>> 	
>> 	   def nth_dash(n)
>> 	      dashes = []
>> 	      @white_pieces.each_with_index { |ch, i| dashes << i if ch  
>> == '-' }
>> 	      dashes[n]
>> 	   end
>>
>
> If you're going to make the change
>
> -   q, @bishop_index = (number - 1).divmod 16
> +   q, @bishop_index = number.divmod 16
>
> then, to maintain consistency, you've got to make the following  
> changes as well:
>
>> 	if __FILE__ == $0
>> 	   begin
>
> -              if ARGV.empty? then n = 1 + rand(960)
> +              if ARGV.empty? then n = rand(960)
>
>
>> 	      else
>> 	         n = ARGV.first.to_i
>
> -	          raise StandardError unless (1..960).include?(n)
> +	          raise StandardError unless (0..959).include?(n)
>
>> 	      end
>> 	      puts "Initial position #{n}"
>> 	      print Chess960.new(n).to_s
>> 	   rescue StandardError
>> 	      puts "Usage:  #{$PROGRAM_NAME} [<integer>]"
>
> -	       puts "where <integer> is in 1..960"
> +	       puts "where <integer> is in 0..959"
>
>> 	      puts "Omitting <integer> produces a random initial position"
>> 	   end
>> 	end

You're absolutely right.  Thanks for pointing that out.

James Edward Gray II