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====== Chess - Programming - Polyglot Book Format - Castle ======

**Castle** is part of the [[Chess:Programming:Polyglot Book Format:Key|Key]]

It is the exclusive or of entries from the **RANDOM_CASTLE** sub-array.

The offsets are computed as:

^Color^Castle Side^Offset^
|White|King-side Castle|0|
|White|Queen-side Castle|1|
|Black|King-side Castle|2|
|Black|Queen-side Castle|3|

<WRAP info>
**NOTE:**  These flags are all true in the starting position and are only updated **after** the appropriate King, Rook or Castling moves.

  * The default value for this field should be 0 if if none of these flags apply; i.e. then castle=0.

</WRAP>


<WRAP important>
**WARNING:** Even though the flag may indicate that castleling can be done, a program should verify that a Castle-move is actually valid, as some mistakes may creep in.
</WRAP>