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Clarify the mapping of files to queenside

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This patch replaces the obscure expressions mapping files ABCDEFGH to ABCDDCBA
by explicite calls 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 check that the current
code for the auxiliary function is optimal.

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

Achieved with a bit of help from Sopel97, snicolet and vondele, thanks everyone!
Closes https://github.com/official-stockfish/Stockfish/pull/2325

No functional change
This commit is contained in:
nickpelling
2019-09-21 08:59:32 +01:00
committed by Stéphane Nicolet
parent defa1ccaa9
commit d232a4ae68
5 changed files with 9 additions and 7 deletions
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9
src/types.h
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@@ -43,6 +43,7 @@
#include <climits>
#include <cstdint>
#include <cstdlib>
#include <algorithm>
#if defined(_MSC_VER)
// Disable some silly and noisy warning from MSVC compiler
@@ -358,14 +359,14 @@ constexpr Square operator~(Square s) {
return Square(s ^ SQ_A8); // Vertical flip SQ_A1 -> SQ_A8
}
constexpr File operator~(File f) {
return File(f ^ FILE_H); // Horizontal flip FILE_A -> FILE_H
}
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);
}