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Clarify the mapping of files to queenside

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Author: @nickpelling

We replace in the code the obscure expressions mapping files ABCDEFGH to ABCDDCBA
by an explicite call to an auxiliary function :

  old:   f = min(f, ~f)
  new:   f = map_to_queenside(f)

We used the Golbolt web site (https://godbolt.org) to find the optimal code
for the auxiliary function.

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 30292 W: 6756 L: 6651 D: 16885
http://tests.stockfishchess.org/tests/view/5d8676720ebc5971531d6aa1

No functional change
This commit is contained in:
Stéphane Nicolet
2019-09-23 08:52:27 +02:00
parent 770c8d92f3
commit 7756344d5d
4 changed files with 7 additions and 3 deletions
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4
src/types.h
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@@ -366,6 +366,10 @@ constexpr Piece operator~(Piece pc) {
return Piece(pc ^ 8); // Swap color of piece B_KNIGHT -> W_KNIGHT
}
inline File map_to_queenside(File f) {
return std::min(f, File(FILE_H - f)); // Map files ABCDEFGH to files ABCDDCBA
}
constexpr CastlingRights operator&(Color c, CastlingRights cr) {
return CastlingRights((c == WHITE ? WHITE_CASTLING : BLACK_CASTLING) & cr);
}