feat(movegen): add pseudo-legal and legal move generation with perft

MoveGen.scala

@@ -0,0 +1,140 @@
+package gambit
+
+object MoveGen:
+
+  def generatePseudo(pos: Position, list: MoveList, capturesOnly: Boolean = false): Unit =
+    val us = pos.sideToMove
+    val them = us ^ 1
+    val board = pos.board
+    var sq = 0
+    while sq < 128 do
+      if Square.onBoard(sq) then
+        val piece = board(sq)
+        if piece != Piece.Empty && (piece >> 3) == us then
+          Piece.typeOf(piece) match
+            case Piece.Pawn   => pawnMoves(pos, sq, us, them, list, capturesOnly)
+            case Piece.Knight => stepMoves(pos, sq, them, Directions.knight, list, capturesOnly)
+            case Piece.King   => stepMoves(pos, sq, them, Directions.king, list, capturesOnly)
+            case Piece.Bishop => slideMoves(pos, sq, them, Directions.bishop, list, capturesOnly)
+            case Piece.Rook   => slideMoves(pos, sq, them, Directions.rook, list, capturesOnly)
+            case Piece.Queen =>
+              slideMoves(pos, sq, them, Directions.bishop, list, capturesOnly)
+              slideMoves(pos, sq, them, Directions.rook, list, capturesOnly)
+            case _ => ()
+      sq += 1
+    if !capturesOnly then castlingMoves(pos, us, them, list)
+
+  private def pawnMoves(
+      pos: Position,
+      sq: Int,
+      us: Int,
+      them: Int,
+      list: MoveList,
+      capturesOnly: Boolean
+  ): Unit =
+    val board = pos.board
+    val forward = if us == Color.White then 16 else -16
+    val startRank = if us == Color.White then 1 else 6
+    val promoRank = if us == Color.White then 7 else 0
+
+    val one = sq + forward
+    if Square.onBoard(one) && board(one) == Piece.Empty then
+      if Square.rankOf(one) == promoRank then addPromotions(sq, one, false, list)
+      else if !capturesOnly then
+        list.add(Move.make(sq, one))
+        if Square.rankOf(sq) == startRank then
+          val two = one + forward
+          if board(two) == Piece.Empty then list.add(Move.make(sq, two, double = true))
+
+    var d = 0
+    while d < 2 do
+      val target = sq + forward + (if d == 0 then -1 else 1)
+      if Square.onBoard(target) then
+        val tp = board(target)
+        if tp != Piece.Empty && (tp >> 3) == them then
+          if Square.rankOf(target) == promoRank then addPromotions(sq, target, true, list)
+          else list.add(Move.make(sq, target, capture = true))
+        else if target == pos.epSquare && pos.epSquare >= 0 then
+          list.add(Move.make(sq, target, capture = true, enPassant = true))
+      d += 1
+
+  private def addPromotions(from: Int, to: Int, capture: Boolean, list: MoveList): Unit =
+    list.add(Move.make(from, to, Piece.Queen, capture = capture))
+    list.add(Move.make(from, to, Piece.Rook, capture = capture))
+    list.add(Move.make(from, to, Piece.Bishop, capture = capture))
+    list.add(Move.make(from, to, Piece.Knight, capture = capture))
+
+  private def stepMoves(
+      pos: Position,
+      sq: Int,
+      them: Int,
+      offsets: Array[Int],
+      list: MoveList,
+      capturesOnly: Boolean
+  ): Unit =
+    val board = pos.board
+    var i = 0
+    while i < offsets.length do
+      val t = sq + offsets(i)
+      if Square.onBoard(t) then
+        val tp = board(t)
+        if tp == Piece.Empty then
+          if !capturesOnly then list.add(Move.make(sq, t))
+        else if (tp >> 3) == them then list.add(Move.make(sq, t, capture = true))
+      i += 1
+
+  private def slideMoves(
+      pos: Position,
+      sq: Int,
+      them: Int,
+      offsets: Array[Int],
+      list: MoveList,
+      capturesOnly: Boolean
+  ): Unit =
+    val board = pos.board
+    var i = 0
+    while i < offsets.length do
+      var t = sq + offsets(i)
+      var stop = false
+      while Square.onBoard(t) && !stop do
+        val tp = board(t)
+        if tp == Piece.Empty then
+          if !capturesOnly then list.add(Move.make(sq, t))
+          t += offsets(i)
+        else
+          if (tp >> 3) == them then list.add(Move.make(sq, t, capture = true))
+          stop = true
+      i += 1
+
+  private def castlingMoves(pos: Position, us: Int, them: Int, list: MoveList): Unit =
+    val board = pos.board
+    if us == Color.White then
+      if (pos.castling & Castling.WhiteKing) != 0 &&
+        board(5) == Piece.Empty && board(6) == Piece.Empty &&
+        !pos.isAttacked(4, them) && !pos.isAttacked(5, them) && !pos.isAttacked(6, them)
+      then list.add(Move.make(4, 6, castle = true))
+      if (pos.castling & Castling.WhiteQueen) != 0 &&
+        board(1) == Piece.Empty && board(2) == Piece.Empty && board(3) == Piece.Empty &&
+        !pos.isAttacked(4, them) && !pos.isAttacked(3, them) && !pos.isAttacked(2, them)
+      then list.add(Move.make(4, 2, castle = true))
+    else
+      if (pos.castling & Castling.BlackKing) != 0 &&
+        board(117) == Piece.Empty && board(118) == Piece.Empty &&
+        !pos.isAttacked(116, them) && !pos.isAttacked(117, them) && !pos.isAttacked(118, them)
+      then list.add(Move.make(116, 118, castle = true))
+      if (pos.castling & Castling.BlackQueen) != 0 &&
+        board(113) == Piece.Empty && board(114) == Piece.Empty && board(115) == Piece.Empty &&
+        !pos.isAttacked(116, them) && !pos.isAttacked(115, them) && !pos.isAttacked(114, them)
+      then list.add(Move.make(116, 114, castle = true))
+
+  def generateLegal(pos: Position, list: MoveList): Unit =
+    val pseudo = new MoveList()
+    generatePseudo(pos, pseudo)
+    val mover = pos.sideToMove
+    var i = 0
+    while i < pseudo.size do
+      val m = pseudo(i)
+      val undo = pos.make(m)
+      if !pos.isAttacked(pos.kingSquare(mover), pos.sideToMove) then list.add(m)
+      pos.unmake(m, undo)
+      i += 1