Simplifies the castling code.

aryann · Oct 17, 2024 · bf4eb91 · bf4eb91
1 parent d66bb5c
commit bf4eb91
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Showing 6 changed files with 43 additions and 66 deletions.
diff --git a/engine/src/board.test.ts b/engine/src/board.test.ts
@@ -514,7 +514,7 @@ describe("castling rights", () => {
 });
 
 describe("castling", () => {
-  it("K king side", () => {
+  it("K", () => {
     const board = new BoardState();
 
     // Make space for a castle:
@@ -526,14 +526,15 @@ describe("castling", () => {
     board.move({ type: "normal", from: "c7", to: "c6" });
 
     // Castling move:
-    board.move({ type: "normal", from: "e1", to: "g1" });
+    board.move({ type: "castling", from: "e1", to: "g1", side: "K" });
+
     assert.equal(
       board.fen(),
       "rnbqkbnr/3ppppp/ppp5/8/8/4PN2/PPPPBPPP/RNBQ1RK1 b kq - 1 4"
     );
   });
 
-  it("K queen side", () => {
+  it("Q", () => {
     const board = new BoardState();
 
     // Make space for a castle:
@@ -547,14 +548,15 @@ describe("castling", () => {
     board.move({ type: "normal", from: "d7", to: "d6" });
 
     // Castling move:
-    board.move({ type: "normal", from: "e1", to: "c1" });
+    board.move({ type: "castling", from: "e1", to: "c1", side: "Q" });
+
     assert.equal(
       board.fen(),
       "rnbqkbnr/4pppp/pppp4/8/8/2NPB3/PPPQPPPP/2KR1BNR b kq - 1 5"
     );
   });
 
-  it("k king side", () => {
+  it("k", () => {
     const board = new BoardState();
 
     // Make space for a castle:
@@ -567,15 +569,15 @@ describe("castling", () => {
     board.move({ type: "normal", from: "d2", to: "d3" });
 
     // Castling move:
-    board.move({ type: "normal", from: "e8", to: "g8" });
+    board.move({ type: "castling", from: "e8", to: "g8", side: "k" });
 
     assert.equal(
       board.fen(),
       "rnbq1rk1/ppppbppp/4pn2/8/8/PPPP4/4PPPP/RNBQKBNR w KQ - 1 5"
     );
   });
 
-  it("k queen side", () => {
+  it("q", () => {
     const board = new BoardState();
 
     // Make space for a castle:
@@ -590,7 +592,7 @@ describe("castling", () => {
     board.move({ type: "normal", from: "e2", to: "e3" });
 
     // Castling move:
-    board.move({ type: "normal", from: "e8", to: "c8" });
+    board.move({ type: "castling", from: "e8", to: "c8", side: "q" });
 
     assert.equal(
       board.fen(),

diff --git a/engine/src/board.ts b/engine/src/board.ts
@@ -1,3 +1,4 @@
+import { CASTLING_ROOK_MOVES } from "./castling.ts";
 import {
   getFile,
   getRank,
@@ -117,8 +118,8 @@ export class BoardState {
       case "castling":
         this.board[toIndex] = this.board[fromIndex];
 
-        const rookFromIndex = this.toIndex(move.rook.from);
-        const rookToIndex = this.toIndex(move.rook.to);
+        const rookFromIndex = this.toIndex(CASTLING_ROOK_MOVES[move.side].from);
+        const rookToIndex = this.toIndex(CASTLING_ROOK_MOVES[move.side].to);
         this.board[rookToIndex] = this.board[rookFromIndex];
 
         this.board[fromIndex] = 0;
@@ -134,7 +135,6 @@ export class BoardState {
     }
     this.isWhiteTurn = !this.isWhiteTurn;
 
-    this.maybeMakeCastlingMove(from, to);
     this.updateCastlingRights(from);
     this.updateEnPassant(from, to, piece);
 
@@ -192,8 +192,12 @@ export class BoardState {
       case "castling":
         this.board[fromIndex] = this.board[toIndex];
 
-        const rookFromIndex = this.toIndex(state.move.rook.from);
-        const rookToIndex = this.toIndex(state.move.rook.to);
+        const rookFromIndex = this.toIndex(
+          CASTLING_ROOK_MOVES[state.move.side].from
+        );
+        const rookToIndex = this.toIndex(
+          CASTLING_ROOK_MOVES[state.move.side].to
+        );
         this.board[rookFromIndex] = this.board[rookToIndex];
 
         this.board[toIndex] = 0;
@@ -286,38 +290,6 @@ export class BoardState {
     return castlingRights.join("");
   }
 
-  // TODO(aryann): Remove this helper. All this logic has been moved to the move
-  // generator. We retain this logic here because the unit tests currently
-  // depend on them.
-  private maybeMakeCastlingMove(from: TSquare, to: TSquare) {
-    const fromIndex = this.toIndex(from);
-    const castlingRights = this.castlingRights;
-
-    if (
-      (from === "e1" && to === "g1" && castlingRights.K) ||
-      (from === "e8" && to === "g8" && castlingRights.k)
-    ) {
-      const right = fromIndex + 1;
-      const rookIndex = fromIndex + 3;
-      if (!this.board[right]) {
-        this.board[right] = this.board[rookIndex];
-        this.board[rookIndex] = 0;
-      }
-    }
-
-    if (
-      (from === "e1" && to === "c1" && castlingRights.Q) ||
-      (from === "e8" && to === "c8" && castlingRights.q)
-    ) {
-      const left = fromIndex - 1;
-      const rookIndex = fromIndex - 4;
-      if (!this.board[left]) {
-        this.board[left] = this.board[rookIndex];
-        this.board[rookIndex] = 0;
-      }
-    }
-  }
-
   // Updates the castling rights. This function assumes that the move has
   // already been determined to be valid.
   private updateCastlingRights(from: TSquare) {

diff --git a/engine/src/castling.ts b/engine/src/castling.ts
@@ -0,0 +1,10 @@
+import { TCastlingSides, TSquare } from "./types";
+
+export const CASTLING_ROOK_MOVES: {
+  [key in TCastlingSides]: { from: TSquare; to: TSquare };
+} = {
+  K: { from: "h1", to: "f1" },
+  Q: { from: "a1", to: "d1" },
+  k: { from: "h8", to: "f8" },
+  q: { from: "a8", to: "d8" },
+};
diff --git a/engine/src/moves.test.ts b/engine/src/moves.test.ts
@@ -979,13 +979,13 @@ describe("castling", () => {
         type: "castling",
         from: "e1",
         to: "g1",
-        rook: { from: "h1", to: "f1" },
+        side: "K",
       },
       {
         type: "castling",
         from: "e1",
         to: "c1",
-        rook: { from: "a1", to: "d1" },
+        side: "Q",
       },
     ]);
   });
@@ -1000,7 +1000,7 @@ describe("castling", () => {
         type: "castling",
         from: "e1",
         to: "g1",
-        rook: { from: "h1", to: "f1" },
+        side: "K",
       },
     ]);
   });
@@ -1015,7 +1015,7 @@ describe("castling", () => {
         type: "castling",
         from: "e1",
         to: "c1",
-        rook: { from: "a1", to: "d1" },
+        side: "Q",
       },
     ]);
   });
@@ -1030,13 +1030,13 @@ describe("castling", () => {
         type: "castling",
         from: "e8",
         to: "g8",
-        rook: { from: "h8", to: "f8" },
+        side: "k",
       },
       {
         type: "castling",
         from: "e8",
         to: "c8",
-        rook: { from: "a8", to: "d8" },
+        side: "q",
       },
     ]);
   });
@@ -1051,7 +1051,7 @@ describe("castling", () => {
         type: "castling",
         from: "e8",
         to: "g8",
-        rook: { from: "h8", to: "f8" },
+        side: "k",
       },
     ]);
   });
@@ -1066,7 +1066,7 @@ describe("castling", () => {
         type: "castling",
         from: "e8",
         to: "c8",
-        rook: { from: "a8", to: "d8" },
+        side: "q",
       },
     ]);
   });

diff --git a/engine/src/moves.ts b/engine/src/moves.ts
@@ -296,10 +296,7 @@ export class MoveGenerator {
           type: "castling",
           from,
           to: rightRight,
-          rook: {
-            from: (from === "e1" ? "h1" : "h8") as TSquare,
-            to: (from === "e1" ? "f1" : "f8") as TSquare,
-          },
+          side: getSide(piece) === "w" ? "K" : "k",
         });
       }
     }
@@ -315,10 +312,7 @@ export class MoveGenerator {
           type: "castling",
           from,
           to: leftLeft,
-          rook: {
-            from: (from === "e1" ? "a1" : "a8") as TSquare,
-            to: (from === "e1" ? "d1" : "d8") as TSquare,
-          },
+          side: getSide(piece) === "w" ? "Q" : "q",
         });
       }
     }

diff --git a/engine/src/types.ts b/engine/src/types.ts
@@ -113,12 +113,11 @@ export type TCastlingRights = {
   q: boolean;
 };
 
-export type TMove = {
-  from: TSquare;
-  to: TSquare;
-} & (
+export type TCastlingSides = "K" | "Q" | "k" | "q";
+
+export type TMove = { from: TSquare; to: TSquare } & (
   | { type: "normal" }
   | { type: "promotion"; promoteTo: TPiece }
   | { type: "enPassant" }
-  | { type: "castling"; rook: { from: TSquare; to: TSquare } }
+  | { type: "castling"; side: TCastlingSides }
 );