xchess/lib/hash.js

Chess Engine

export {stateToHash, boardToHash}

function stateToHash(state){
	return hash.stateToHash(state);
}

function boardToHash(board){
	return hash.boardToHash(board);
}

import {squares} from './square.js'

const MaxGapLength = 19n;
const MaxShortGapLength = 3n;

class HashWriter {

	value;
	gapLength = 0n;

	stateToHash(state){
		this.value = 1n;
		this.state(state);
		return this.value;
	}

	boardToHash(board){
		this.value = 1n;
		this.board(board);
		return this.value;
	}

	push(value, size){
		this.value <<= size;
		this.value |= BigInt(value);
	}

	board(board){
		for(const square of squares)
			this.square(board.get(square));
		this.releaseGap();
	}

	square(piece){
		piece ? this.piece(piece) : this.skip();
	}

	piece(piece){
		this.releaseGap();
		this.push(piece.code, 4n);
	}

	skip(){
		this.gapLength ++;
		if(this.gapLength >= MaxGapLength)
			this.gap();
	}

	releaseGap(){
		if(this.gapLength > 0n)
			this.gap();
	}

	gap(){
		if(this.gapLength > MaxShortGapLength)
			this.longGap(this.gapLength);
		else
			this.shortGap(this.gapLength);
		this.gapLength = 0n;
	}

	shortGap(value){
		this.push(value + 11n, 4n);
	}

	longGap(value){
		this.push(value + 236n, 8n);
	}

	state({color, enPassantTarget, wk, wq, bk, bq, board}){
		this.push(color, 1n);
		this.push(wk, 1n);
		this.push(wq, 1n);
		this.push(bk, 1n);
		this.push(bq, 1n);
		if(enPassantTarget){
			this.push(1n, 1n);
			this.push(enPassantTarget, 6n);
		} else this.push(0n, 1n);
		this.board(board);
	}
}

const hash = new HashWriter();