private function FindTilesAttackedByPawn($nRank, $nFile)
{
$this->nCalls++;
$nTile = $nRank * 8 + $nFile;
$n64AttackedTiles = 0;
$n64Occupied = 0;
// Need to use different bitmap arrays for the players.
if ($this->PlayerTurn == 0) {
// Get the tile(s) that can be theoretically moved to.
$n64AttackedTiles = $this->WPawnAttacks[$nTile]->duplicate();
// If this is the starting rank for pawn then see if the two tiles above are free.
if ($nRank == 1) {
// Check that the tile in rank 3 is free. If not then rank 4 cannot be reached.
$n64Occupied = BitBoard::_AND_($this->n64All, $this->Tiles[$nTile + 8]);
if ($n64Occupied->is_zero()) {
// Check if rank 4 is free. If not then exclusive or to remove that tile from
// the bitmap.
$n64Occupied = BitBoard::_AND_($this->n64All, $this->Tiles[$nTile + 16]);
if (!$n64Occupied->is_zero()) {
$n64AttackedTiles->_XOR($n64Occupied);
}
} else {
$n64AttackedTiles->set_value('0x0');
}
// Set to 0 since neither tile can be reached.
} else {
if ($nRank < 7) {
// Check that the rank above can be moved to by masking the ALL pieces bitmap
// with the tile above the current position, to see if the tile is occupied.
// If it is then remove this tile from the attack bitmap.
$n64Occupied = BitBoard::_AND_($this->n64All, $this->Tiles[$nTile + 8]);
if (!$n64Occupied->is_zero()) {
$remove = new BitBoard();
$remove->set_value('FFFFFFFFFFFFFFFF');
$remove->_XOR($this->Tiles[$nTile + 8]);
$n64AttackedTiles->_AND($remove);
}
}
}
// Now check if capturing a piece is possible by ANDing the captures bitmap
// with the all black pieces bitmap and combining this with the AttackedTiles bitmap.
$n64AttackedTiles->_OR(BitBoard::_AND_($this->WPawnCaptures[$nTile], $this->n64BAll));
// Check if en passant is possible, by ANDing the en passant bitmap with the pawn capture
// bitmap for this tile. Then OR this with the attackedtiles bitmap.
$n64AttackedTiles->_OR(BitBoard::_AND_($this->n64Enpassant, $this->WPawnCaptures[$nTile]));
} else {
$n64AttackedTiles = $this->BPawnAttacks[$nTile]->duplicate();
if ($nRank == 6) {
$n64Occupied = BitBoard::_AND_($this->n64All, $this->Tiles[$nTile - 8]);
if ($n64Occupied->is_zero()) {
$n64Occupied = BitBoard::_AND_($this->n64All, $this->Tiles[$nTile - 16]);
if (!$n64Occupied->is_zero()) {
$n64AttackedTiles->_XOR($n64Occupied);
}
} else {
$n64AttackedTiles->set_value('0x0');
}
// Set to 0 since neither tile can be reached.
} else {
if ($nRank > 0) {
$n64Occupied = BitBoard::_AND_($this->n64All, $this->Tiles[$nTile - 8]);
if (!$n64Occupied->is_zero()) {
$remove = new BitBoard();
$remove->set_value('FFFFFFFFFFFFFFFF');
$remove->_XOR($this->Tiles[$nTile - 8]);
$n64AttackedTiles->_AND($remove);
}
}
}
$n64AttackedTiles->_OR(BitBoard::_AND_($this->BPawnCaptures[$nTile], $this->n64WAll));
$n64AttackedTiles->_OR(BitBoard::_AND_($this->n64Enpassant, $this->BPawnCaptures[$nTile]));
}
return $n64AttackedTiles;
}