fix bug in handling of pinned en-passant captures

stephenjlovell · stephenjlovell · commit e840be0914d9 · 2017-02-06T21:22:58.000-05:00
diff --git a/attack.go b/attack.go
@@ -53,6 +53,10 @@ func isAttackedBy(brd *Board, occ BB, sq int, attacker, defender uint8) bool {
 	return false
 }
 
+func pinnedCanMove(brd *Board, from, to int, c, e uint8) bool {
+	return isPinned(brd, brd.AllOccupied(), from, c, e)&sqMaskOn[to] > 0
+}
+
 // Determines if a piece is blocking a ray attack to its king, and cannot move off this ray
 // without placing its king in check.
 // Returns the area to which the piece can move without leaving its king in check.
@@ -62,15 +66,13 @@ func isAttackedBy(brd *Board, occ BB, sq int, attacker, defender uint8) bool {
 // 3. Scan in the opposite direction to see detect any potential threats along this ray.
 
 // Return a bitboard of locations the piece at sq can move to without leaving the king in check.
-func isPinned(brd *Board, sq int, c, e uint8) BB {
-	occ := brd.AllOccupied()
+
+func isPinned(brd *Board, occ BB, sq int, c, e uint8) BB {
 	var line, attacks, threat BB
 	kingSq := brd.KingSq(c)
-	dir := directions[sq][kingSq] // get direction toward king
-
 	line = lineMasks[sq][kingSq]
 	if line > 0 { // can only be pinned if on a ray to the king.
-		if dir < NORTH {
+		if directions[sq][kingSq] < NORTH { // direction toward king
 			attacks = bishopAttacks(occ, sq)
 			threat = line & attacks & (brd.pieces[e][BISHOP] | brd.pieces[e][QUEEN])
 		} else {
@@ -116,12 +118,14 @@ func getSee(brd *Board, from, to int, capturedPiece Piece) int {
 	count := 1
 
 	if capturedPiece == KING {
-		// this move is illegal and will be discarded by search.  return the lowest possible
+		// this move is illegal and will be discarded by the move selector. Return the lowest possible
 		// SEE value so that this move will be put at end of list.  If cutoff occurs before then,
 		// the cost of detecting the illegal move will be saved.
-
 		fmt.Println("info string king capture detected in getSee()!")
-		return SEE_MIN
+		fmt.Printf("info string %s%s x %s", SquareString(from), SquareString(to), sanChars[capturedPiece])
+		brd.Print()
+		panic("king capture detected in getSee()!")
+		// return SEE_MIN
 	}
 	t = brd.TypeAt(from)
 	if t == KING { // Only commit to the attack if target piece is undefended.
@@ -191,10 +195,6 @@ func getSee(brd *Board, from, to int, capturedPiece Piece) int {
 	return pieceList[0]
 }
 
-func pinnedCanMove(brd *Board, from, to int, c, e uint8) bool {
-	return isPinned(brd, from, brd.c, brd.Enemy())&sqMaskOn[to] > 0
-}
-
 func isCheckmate(brd *Board, inCheck bool) bool {
 	if !inCheck {
 		return false
diff --git a/move_gen.go b/move_gen.go
@@ -533,8 +533,8 @@ func getEvasions(brd *Board, htable *HistoryTable, winning, losing, remainingMov
 				// In addition to making sure this capture will get the king out of check and that
 				// the piece is not pinned, verify that removing the enemy pawn does not leave the
 				// king in check.
-				if (sqMaskOn[to]&defenseMap) > 0 && pinnedCanMove(brd, from, to, c, e) &&
-					isPinned(brd, int(enpTarget), c, e)&sqMaskOn[to] > 0 {
+				if (sqMaskOn[to]&defenseMap) > 0 && isPinned(brd, occ&sqMaskOff[enpTarget],
+					m.From(), brd.c, brd.Enemy())&sqMaskOn[m.To()] > 0 {
 					m = NewCapture(from, to, PAWN, PAWN)
 					winning.Push(SortItem{SortCapture(PAWN, PAWN, 0), m})
 				}
@@ -564,7 +564,7 @@ func getEvasions(brd *Board, htable *HistoryTable, winning, losing, remainingMov
 			from = furthestForward(c, f) // Locate each knight for the side to move.
 			// Knights cannot move if pinned by a sliding piece, since they can't move along the ray between
 			// the threat piece and their own king.
-			if isPinned(brd, from, c, e) == BB(ANY_SQUARE_MASK) {
+			if isPinned(brd, occ, from, c, e) == BB(ANY_SQUARE_MASK) {
 				for t := (knightMasks[from] & defenseMap); t > 0; t.Clear(to) { // generate to squares
 					to = furthestForward(c, t)
 					if sqMaskOn[to]&enemy > 0 {
diff --git a/move_validation.go b/move_validation.go
@@ -19,15 +19,20 @@ func (brd *Board) LegalMove(m Move, inCheck bool) bool {
 // Moves generated while in check should already be legal, since we determine this
 // as a side-effect of generating evasions.
 func (brd *Board) AvoidsCheck(m Move, inCheck bool) bool {
-	return inCheck || brd.PseudolegalAvoidsCheck(m)
+	// return inCheck || brd.PseudolegalAvoidsCheck(m)
+	if inCheck && !brd.PseudolegalAvoidsCheck(m) {
+		fmt.Println("{!}")
+	}
+	return brd.PseudolegalAvoidsCheck(m)
 }
 
 func (brd *Board) PseudolegalAvoidsCheck(m Move) bool {
 	switch m.Piece() {
 	case PAWN:
 		if m.CapturedPiece() == PAWN && brd.TypeAt(m.To()) == EMPTY { // En-passant
-			return pinnedCanMove(brd, m.From(), m.To(), brd.c, brd.Enemy()) &&
-				isPinned(brd, int(brd.enpTarget), brd.c, brd.Enemy())&sqMaskOn[m.To()] > 0
+			// detect if the moving pawn would be pinned in the absence of the captured pawn.
+			return isPinned(brd, brd.AllOccupied()&sqMaskOff[brd.enpTarget],
+				m.From(), brd.c, brd.Enemy())&sqMaskOn[m.To()] > 0
 		} else {
 			return pinnedCanMove(brd, m.From(), m.To(), brd.c, brd.Enemy())
 		}
@@ -56,9 +61,9 @@ func (brd *Board) EvadesCheck(m Move) bool {
 
 		if threats == 0 {
 			fmt.Println("info string EvadesCheck() called from non-check position!")
-			// m.Print()
-			// brd.PrintDetails()
-			return true // no threats to evade.
+			brd.Print()
+			m.Print()
+			return brd.PseudolegalAvoidsCheck(m)
 		}
 
 		if popCount(threats) > 1 {
@@ -101,8 +106,8 @@ func (brd *Board) ValidMove(m Move, inCheck bool) bool {
 		// fmt.Printf("To square occupied by own piece!{%s}", m.ToString())
 		return false
 	}
-	if capturedPiece == KING || brd.pieces[c][KING] == 0 {
-		// fmt.Printf("King capture detected!{%s}", m.ToString())
+	if capturedPiece == KING {
+		fmt.Printf("info string King capture detected in ValidMove! (%s)\n", m.ToString())
 		return false
 	}
 	switch piece {
