# Diagonal Mirroring

Home * Chess * Position * Diagonal Mirroring

Hilma af Klint - Group IX SUW, The Swan No. 7 [1]

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.

# 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;
}
```

# 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 - -