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chess.js
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chess.js
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
//(c)2010 Oscar Toledo G.
// Chessboard structure (array "board"):
// 0 1 2 3 4 5 6 7 8 9
// 00 -- -- -- -- -- -- -- -- -- --
// 10 -- -- -- -- -- -- -- -- -- --
// 20 -- A8 B8 C8 D8 E8 F8 G8 H8 --
// 30 -- A7 B7 C7 D7 E7 F7 G7 H7 --
// 40 -- A6 B6 C6 D6 E6 F6 G6 H6 --
// 50 -- A5 B5 C5 D5 E5 F5 G5 H5 --
// 60 -- A4 B4 C4 D4 E4 F4 G4 H4 --
// 70 -- A3 B3 C3 D3 E3 F3 G3 H3 --
// 80 -- A2 B2 C2 D2 E2 F2 G2 H2 --
// 90 -- A1 B1 C1 D1 E1 F1 G1 H1 --
// 100 -- -- -- -- -- -- -- -- -- --
// 110 -- -- -- -- -- -- -- -- -- --
//
// Piece codes:
// 1 - pawn 4 - bishop
// 2 - king 5 - rook
// 3 - knight 6 - queen
//
// White pieces or'ed with 0x08, pieces that wasn't moved or'ed with 0x10.
// So, for example, white king has code 0x1A and after it's first move becomes 0x0A.
// Area outside of the chessboard filled with 0x07, empty cells contain 0x00.
var B, // source position of the move
i, // current piece code
y, // current player: 0 - white, 8 - black
u, // position of pawn after two-square move, 0 after any other move
b, // target position of the move
I = [],
board = [], // chessboard (12 rows x 10 columns, see wiki for more info)
G = 120,
x = 10, // just ten ;)
z = 15, // just fifteen ;)
M = 10000,
piecesCosts = [0,99,0,306,297,495,846], // cost of the pieces (empty,pawn,king,knight,bishop,rook,queen)
rowsCosts = [-1,0,1,2,2,1,0,-1]; // cost of the rows/columns
function movesForPiece(piece) {
var moves = [
[9,11,10,20], // black pawn
[-1,1,-10,10,-11,-9,9,11], // king
[-21,-19,-12,-8,8,12,19,21], // knight
[-11,-9,9,11], // bishop
[-1,1,-10,10], // rook
[-1,1,-10,10,-11,-9,9,11] // queen
];
// for white pawn
if ((piece & 15) == 9)
return [-9,-11,-10, -20];
// for other pieces
return moves[(piece & 7) - 1];
}
function executeMove(O, p, n, m, g) {
board[p] = n;
if (m) {
board[g] = board[m];
board[m] = 0;
} else if (g) {
board[g] = 0;
}
board[O] = 0;
}
function undoMove(O, p, o, r, m, g) {
board[O] = o;
board[p] = r;
if (m) {
board[m] = board[g];
board[g] = 0;
} else if (g) {
board[g] = 9 ^ y;
}
}
// When w=0 function scans all possible moves, otherwise just that ends up at w
// c - cutoff threshold. Function returns if h>0 and move with heuristic greater than c found
// h - current depth (starts with 0)
// e - cell from which moves enumeration starts (usually 21, "A8")
// S - position of pawn after two-square move, 0 after any other move
// s - scan depth (1 - verify B -> b and execute it,
// 0 - used for check checking (returns above 70k when opponent's king under attack)
function X(w,c,h,e,S,s) {
var t,
o, // board?
L, // heuristic of the current move
E, // also board?
d, //magic setting
O = e,
N = -M*M, // heuristic of the best move
K = (78 - h) << x, // cost of the check
p,
g, // "en passant" or castling target position
n,
m, // castling source position
q,
r,
C,
J,
a = y ? -x : x, // +10 for white, -10 for black
moves;
y ^= 8;
G++;
//magic settings
d = w || (s && s>=h && X(0,0,0,21,0,0) > M);
// loop for all cells starting with e (usually 21, "A8") and finishing just before e
// O - current cell, read-only inside loop
do {
p = O; // current position
o = board[p]; // current piece code (or'ed with 16) or 0 or 7
if (o) { // if cell doesn't empty
q = o & z ^ y; // current piece code (1..6 for current player, 9..14 for opponent, 7 or 15 - outside)
if (q < 7) {
q--;
moves = movesForPiece(o);
C = 0;
// q decreased: 0 pawn, 1 king, 2 knight, 3 bishop, 4 rook, 5 queen
// check each possible move of the current piece
// C,q,o are read-only inside loop
do {
p += moves[C]; // target cell position
r = board[p]; // piece code at the target cell, read-only below
if (!w | p == w) { // required target cell not specified or equals to current target
g = (q == 0 && p + a == S) ? S : 0; // en passant
if ((!r & (!!q | C>1 || !!g)) || ((r+1&z^y)>9 && (q | C<2))) {
m = !(r - 2 & 7); // king on the target cell, check!
if (m) {
y ^= 8;
I[G--] = O;
return K;
}
// m is 0 after this point
J = n = o & z; // J & n - current piece code
E = board[p - a] & z; // piece at the cell above target (for white) or below target (for black)
// for pawn on the last line loop runs from n=3 (or 11) to t=6 (or 14) (promotions)
// for king loop can run two times if castling is possible
// for any other piece loop runs only once with n = t = piece code
t = (q | E-7) ? n : (n+=2,6^y);
while (n <= t) {
// Heuristic:
// For attack moves:
// + attacked piece cost
// pawn: 99, knight: 306, bishop: 297, rook: 495, queen: 846
// - attacker piece cost
// pawn: 0, king: 1, knight: 2, bishop: 3, rook: 4, queen: 5
// - current depth
// For king:
// +9 for castling
// For all except king:
// + for target row
// - for source row
// 1:-1, 2:0, 3:1, 4:2, 5:2, 6:1, 7:0, 8:-1
// + for target column (doubled for pawns)
// - for source column
// A:-1, B:0, C:1, D:2, E:2, F:1, G:0, H:-1
// +8 if piece doesn't moved before
// For pawn:
// -99 if current move isn't "en passant"
// +1 if have own pawn to the left/right of the target cell
// + for promotion:
// knight: 306, bishop: 297, rook: 495, queen: 846
// +1 for two-square move
// For all:
// +1 for blocking opponent's pawn
L = r ? piecesCosts[r&7]-h-q : 0; // value of the attacked piece (0 for empty cell)
if (s) {
L+=((1-q) ? rowsCosts[(p-p%x)/x-2] - rowsCosts[(O-O%x)/x-2] +
rowsCosts[p%x-1]*(q?1:2) - rowsCosts[O%x-1] + (o&16)/2
: !!m * 9) +
(!q ? !(board[p-1]^n) + !(board[p+1]^n) + piecesCosts[n&7] - 99 + !!g * 99 + (C == 3)
: 0) +
!(E ^ y ^ 9);
}
if ((s > h) || ((1<s & s==h) && (L>z | d))) {
// execute move
executeMove(O, p, n, m, g);
// find opponent's best move
J = (q | C<3) ? 0 : p;
L -= X((s > h | d) ? 0 : p,
L - N,
h + 1,
I[G+1],
J,
s);
// if we in check mode (s==1) and current move (O,p,n) same as player's (B,b,i)
// and move is possible then update chessboard and return
if (!h && s == 1 && B == O && i == n && p == b && L >= -M) {
DrawPieces();
G--;
u = J;
return u;
}
// is castling possible?
J = (q-1 | C>1) || m || (!s | d | r | o<z) || X(0,0,0,21,0,0) > M;
// undo move
undoMove(O, p, o, r, m, g);
}
// if current move has better heuristic
if (L>N || (s>1 && L==N && !h && Math.random()<.5)) {
I[G] = O;
if (s > 1) {
// cutoff
if (h && L > c) {
y ^= 8;
G--;
return L;
}
// output this move
if (!h) {
i = n;
B = O;
b = p;
}
}
N = L;
}
// try castling if J == 0
n += J || (g = p,
m = (p < O) ? g-3 : g+2,
(board[m] < z | board[m+O-p]) || board[p+=p-O]) ? 1 : 0;
}
}
}
// If target cell was empty and current piece is rook, queen or bishop -
// try to move further in same direction. otherwise try next move from table
// skip two-square move for pawn if it was moved, or square ahead of it is occupied.
} while ((!r & q>2) || (p=O, (q | C < 2 | o > z & !r) && (++C < moves.length)));
}
}
} while ((++O > 98) ? O = 20 : e - O);
y ^= 8;
G--;
return (N + M*M && (N > 1924-K | d)) ? N : 0;
}
y = u = 0;
function SetupChessboard() {
var x, y;
var i = 0;
var initial = [
5, 3, 4, 6, 2, 4, 3, 5,
1, 1, 1, 1, 1, 1, 1, 1,
9, 9, 9, 9, 9, 9, 9, 9,
13, 11, 12, 14, 10, 12, 11, 13
];
for (y=0; y<12; y++) {
for (x=0; x<10; x++) {
if (x<1 || y<2 || x>8 || y>9) {
// outside
board[y*10+x] = 7;
} else if (y>=4 && y<=7) {
// empty
board[y*10+x] = 0;
} else {
// pieces
board[y*10+x] = initial[i++] | 16;
}
}
}
}
function CreateChessboardView() {
var x, y, i;
var a = "<table cellspacing=0 align=center>";
for (y=0; y<8; y++) {
a += "<tr>";
for (x=0; x<8; x++) {
i = y*10 + x + 21;
a += "<th width=60 height=60 onclick=OnClick(" + i + ") id=o" + i +
" style='line-height:50px;font-size:50px;border:2px solid #dde' bgcolor=#" +
(((x+y) & 1) ? "c0c0f0>" : "f0f0f0>");
}
a += "</tr>";
}
a += "<tr><th colspan=8><select id=t style='font-size:20px'>";
a += "<option>♛<option>♜<option>♝<option>♞";
a += "</select></tr></table>";
document.write(a);
}
function DrawPieces() {
var pieces = "\xa0\u265f\u265a\u265e\u265d\u265c\u265b \u2659\u2654\u2658\u2657\u2656\u2655";
var p, q;
B=b;
for (p=21; p<99; ++p) {
if (q = document.getElementById("o" + p)) {
q.innerHTML = pieces.charAt(board[p] & 15);
q.style.borderColor = (p == B) ? "red" : "#dde";
}
}
}
var clickLock = false;
function OnClick(s) {
if (clickLock)
return;
i = (board[s] ^ y) & z;
if (i > 8) {
// clicked on the own piece
b = s;
DrawPieces();
} else if (B && i<9) {
// clicked on the opponent piece or empty space
b = s;
i = board[B] & z;
// pawn promotion
if ((i & 7) == 1 & (b < 29 | b > 90))
i = 14 - document.getElementById("t").selectedIndex ^ y;
// verify player move and execute it
X(0,0,0,21,u,1);
// Call A.I. after some delay
if (y) {
clickLock = true;
setTimeout("X(0,0,0,21,u,2/*ply*/);X(0,0,0,21,u,1);clickLock=false;",250);
}
}
}
SetupChessboard();
CreateChessboardView();
DrawPieces();
i = 100;
</script>
</body>
</html>