Add delta pruning (#15)

Add delta pruning based on futility pruning

README.md

@@ -76,6 +76,7 @@ Note that the config file is compiled with the engine itself, so if you are usin
 * Transposition table.
 * Null-move pruning.
 * Futility pruning.
+* Delta pruning.
 * Late move reductions.
 * Search extensions:
     * Check extensions.

catto.config.js

@@ -1,6 +1,6 @@
 module.exports = {
     // Current version to show in UCI
-    version: "v0.8.0",
+    version: "v0.8.1",
     // Late move reduction config
     lmrFullDepth: 4, // Number of moves to be searched in full depth
     lmrMaxReduction: 3, // Only apply LMR above this depth

package.json

@@ -1,6 +1,6 @@
 {
   "name": "catto",
-  "version": "0.8.0",
+  "version": "0.8.1",
   "description": "The Catto chess engine",
   "main": "index.js",
   "scripts": {

src/core.ts

@@ -1,8 +1,7 @@
 import { Chess, Move } from "chess.js";
 import { evaluateBoard } from "./evaluate";
-import { mvv_lva, PIECE_NUM } from "./evaluations";
+import { mvv_lva, PIECE_NUM, mgMaterial } from "./evaluations";
 import { genZobristKey } from "./zobrist";
-import { mgMaterial } from "./evaluations";
 
 export enum HashFlag {
     exact,
@@ -189,6 +188,12 @@ export class Engine {
             return beta;
         }
 
+        // Delta pruning
+        const delta = mgMaterial[4];
+        if (evaluation < alpha - delta) {
+            return alpha;
+        }
+
         // Found a better move
         if (evaluation > alpha) {
             alpha = evaluation;