kate/BadFish
1
0
Fork 0
mirror of https://github.com/sockspls/badfish synced 2025-07-11 19:49:14 +00:00
Code Issues Releases Wiki Activity

Document index[] and pieceList[] are not invariants

Browse source 
Array index[] and pieceList[] are not guaranteed to be
invariant to a do_move() + undo_move() sequence when a
capture move is involved.

The reason is that the captured piece is removed form
the list and substituted with the last one in do_move()
while in undo_move() is added again but at the end of
the list.

Because index[] and pieceList[] are used in move generation
to scan the pieces it means that moves will be generated
in a different order before and after a do_move() + undo_move()
sequence as, for instance, the one in Position::has_mate_threat()

After latest patches, move generation could now be invoked
also by MovePicker c'tor and this explains why order of
picked moves is different if MovePicker object is istantiated
before or after a Position::has_mate_threat() call.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-08-31 10:59:33 +02:00
parent af220cfd52
commit 97dd7568ed
1 changed files with 6 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
src/position.cpp
View file

@ -939,6 +939,12 @@ void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Squ
pieceCount[them][capture]--;
// Update piece list, move the last piece at index[capsq] position
//
// WARNING: this is a not perfectly revresible operation. When we
// will reinsert the captured piece in undo_move() we will put it
// at the end of the list and not in its original place, it means
// index[] and pieceList[] are not guaranteed to be invariant to a
// do_move() + undo_move() sequence.
Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
index[lastPieceSquare] = index[capsq];
pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;