Diagonal Mirroring

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Home * Chess * Position * Diagonal Mirroring

Diagonal mirroring mirrors all pieces along the main diagonal or main anti-diagonal. It is applicable in pawn-less endgames with castling no longer possible. Along with horizontal and/or vertical flipping, diagonal mirroring is used in pawn-less endgame tablebases to restrict a white king to the 10 squares of the a1-d4-d1 triangle of the board.

Sample Position

Original Diagonal Mirror Anti-Diagonal Mirror
    
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    
    
    
    
    
    
       
        
     
        
        
        
        
        
♚       
        
♘♔  ♗   
        
        
        
        
        
    
    
    
    
    
    
    
    
        
        
        
       
        
        
       
      
        
        
        
     ♗  
        
        
     ♔  
     ♘ ♚
    
    
    
    
    
    
    
    
      
       
        
        
       
        
        
        
♚ ♘     
  ♔     
        
        
  ♗     
        
        
        
k7/8/NK2B3/8/8/8/8/8 w - - 8/8/8/5B2/8/8/5K2/5N1k w - - k1N5/2K5/8/8/2B5/8/8/8 w - -

Mirroring an 8x8 Board

An 8x8 Board with a rank-file mapping needs to swap rank and file. A pure 8x8 Board may be mirrored along the main diagonal that way in C:

int board[64], f, r, sm, sq, s;

for (f = 1; f < 8; ++f)
for (r = 0; r < f; ++r)
{
  sq = 8*r + f;
  sm = 8*f + r;
  s = board[sq];
  board[sq] = board[sm];
  board[sm] = s;
}

See also

External Links

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