Allow e.p. capture on triple-Push

Some variants (like Omega Chess) have an initial triple-Push on Pawns,
wich can then e.p.-captured on both of the squares they skip. To allow
the Betza move generator to supply such e.p. captures, a bit flag is
kludged into the EP_RANK state indicator on triple pushes, while the
main value there is that of the rank directly behind the pushed Pawn.
The Betza generator then also matches the square behind it with the
e.p.-capture to-square when the falg is set.
 ApplyMove() also had to be adapted, to remove the Pawn two squares
behind the capturing one, rather than straight behind it, when this
flag is set.

diff --git a/backend.c b/backend.c
index cb564b4..2c7933e 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -9932,8 +9932,8 @@ ApplyMove (int fromX, int fromY, int toX, int toY, int promoChar, Board board)
       if( board[fromY][fromX] == WhitePawn ) {
            if(fromY != toY) // [HGM] Xiangqi sideway Pawn moves should not count as 50-move breakers
               board[EP_STATUS] = EP_PAWN_MOVE;
-           if( toY-fromY==2) {
-               board[EP_FILE] = (fromX + toX)/2; board[EP_RANK] = (fromY + toY)/2;
+           if( toY-fromY>=2) {
+               board[EP_FILE] = (fromX + toX)/2; board[EP_RANK] = toY - 1 | 128*(toY - fromY > 2);
                if(toX>BOARD_LEFT   && board[toY][toX-1] == BlackPawn &&
                        gameInfo.variant != VariantBerolina || toX < fromX)
                      board[EP_STATUS] = toX | berolina;
@@ -9945,8 +9945,8 @@ ApplyMove (int fromX, int fromY, int toX, int toY, int promoChar, Board board)
       if( board[fromY][fromX] == BlackPawn ) {
            if(fromY != toY) // [HGM] Xiangqi sideway Pawn moves should not count as 50-move breakers
               board[EP_STATUS] = EP_PAWN_MOVE;
-           if( toY-fromY== -2) {
-               board[EP_FILE] = (fromX + toX)/2; board[EP_RANK] = (fromY + toY)/2;
+           if( toY-fromY<= -2) {
+               board[EP_FILE] = (fromX + toX)/2; board[EP_RANK] = toY + 1 | 128*(fromY - toY > 2);
                if(toX>BOARD_LEFT   && board[toY][toX-1] == WhitePawn &&
                        gameInfo.variant != VariantBerolina || toX < fromX)
                      board[EP_STATUS] = toX | berolina;
@@ -10039,8 +10039,10 @@ ApplyMove (int fromX, int fromY, int toX, int toY, int promoChar, Board board)
               && (board[toY][toX] == EmptySquare)) {
        board[fromY][fromX] = EmptySquare;
        board[toY][toX] = WhitePawn;
-       captured = board[toY - 1][toX];
-       board[toY - 1][toX] = EmptySquare;
+       if(toY == board[EP_RANK] - 128 + 1)
+           captured = board[toY - 2][toX], board[toY - 2][toX] = EmptySquare;
+       else
+           captured = board[toY - 1][toX], board[toY - 1][toX] = EmptySquare;
     } else if ((fromY == BOARD_HEIGHT-4)
               && (toX == fromX)
                && gameInfo.variant == VariantBerolina
@@ -10102,8 +10104,10 @@ ApplyMove (int fromX, int fromY, int toX, int toY, int promoChar, Board board)
               && (board[toY][toX] == EmptySquare)) {
        board[fromY][fromX] = EmptySquare;
        board[toY][toX] = BlackPawn;
-       captured = board[toY + 1][toX];
-       board[toY + 1][toX] = EmptySquare;
+       if(toY == board[EP_RANK] - 128 - 1)
+           captured = board[toY + 2][toX], board[toY + 2][toX] = EmptySquare;
+       else
+           captured = board[toY + 1][toX], board[toY + 1][toX] = EmptySquare;
     } else if ((fromY == 3)
               && (toX == fromX)
                && gameInfo.variant == VariantBerolina

diff --git a/moves.c b/moves.c
index fa9a8cc..b4edc45 100644 (file)
--- a/moves.c
+++ b/moves.c
@@ -265,7 +265,7 @@ void
 MovesFromString (Board board, int flags, int f, int r, int tx, int ty, int angle, char *desc, MoveCallback cb, VOIDSTAR cl)
 {
     char buf[80], *p = desc, *atom = NULL;
-    int mine, his, dir, bit, occup, i, promoRank = -1;
+    int mine, his, dir, bit, occup, i, ep, promoRank = -1;
     ChessMove promo= NormalMove; ChessSquare pc = board[r][f];
     if(pc == DarkSquare) return; // this is not a piece, but a 'hole' in the board
     if(flags & F_WHITE_ON_MOVE) his = 2, mine = 1; else his = 1, mine = 2;
@@ -426,7 +426,8 @@ MovesFromString (Board board, int flags, int f, int r, int tx, int ty, int angle
                  continue;
                }
                if(hop & 32+64) { if(occup != 4) { if(hop & 64 && i != 1) i = 2; hop &= 31; } continue; } // hopper
-               if(mode & 8 && y == board[EP_RANK] && occup == 4 && board[EP_FILE] == x) { // to e.p. square
+               ep = board[EP_RANK];
+               if(mode & 8 && occup == 4 && board[EP_FILE] == x && (y == (ep & 127) || y - vy == ep - 128)) { // to e.p. square (or 2nd e.p. square)
                    cb(board, flags, mine == 1 ? WhiteCapturesEnPassant : BlackCapturesEnPassant, r, f, y, x, cl);
                }
                if(mode & 1024) {            // castling