// Roughly orders moves in order of most likely to be good to least.
// Examines all checks first, followed by captures, followed by good moves.
// "Good moves" are sorted by their board evaluation after they are played.
// If quiescence is set to true, then only checks and captures are returned.
func orderedMoves(b *engine.Board, quiescence bool) []*engine.Move {
checks := make([]*engine.Move, 0)
captures := make([]*engine.Move, 0)
rest := make([]*engine.Move, 0)
// parentscore := EvalBoard(b)
for _, move := range b.AllLegalMoves() {
b.ForceMove(move)
if b.IsCheck(b.Turn) {
checks = append(checks, move)
} else if move.Capture != 0 {
captures = append(captures, move)
} else if !quiescence {
childscore := EvalBoard(b) * float64(b.Turn*-1)
// if (b.Turn == -1 && childscore > parentscore) || (b.Turn == 1 && childscore < parentscore) {
move.Score = childscore
rest = append(rest, move)
// }
}
b.UndoMove(move)
}
if !quiescence {
sort.Sort(sort.Reverse(ByScore(rest)))
}
orderedmoves := make([]*engine.Move, len(checks)+len(captures)+len(rest))
index := 0
for _, l := range [][]*engine.Move{checks, captures, rest} {
for _, m := range l {
m.Score = 0
orderedmoves[index] = m
index++
}
}
return orderedmoves
}
// Returns the score from the point of view of the person whose turn it is.
// Positive numbers indicate a stronger position.
func EvalBoard(b *engine.Board) (score float64) {
if over := b.IsOver(); over != 0 {
if over == 1 {
return DRAW
} else {
return float64(WIN / 2 * over * b.Turn)
}
}
attackarray := [8][8]int{}
mypawns := [8]int{}
opppawns := [8]int{}
var heavies int // count of opponent's queens and rooks
for _, piece := range b.Board {
// add piece value to score and update attack array
score += float64(VALUES[piece.Name] * piece.Color * b.Turn)
updateAttackArray(b, piece, &attackarray)
if piece.Name == 'p' {
if piece.Color == b.Turn {
mypawns[piece.Position.X-1] += 1
} else {
opppawns[piece.Position.X-1] += 1
}
} else if (piece.Name == 'q' || piece.Name == 'r') && piece.Color == b.Turn*-1 {
heavies += 1
}
}
score += pawnStructureAnalysis(mypawns)
score -= pawnStructureAnalysis(opppawns)
for _, piece := range b.Board {
if piece.Name == 'k' {
if heavies > 1 {
if piece.Color == b.Turn {
score += checkKingSafety(piece.Position.X, mypawns)
} else {
score -= checkKingSafety(piece.Position.X, opppawns)
}
} else {
// endgame stuff
}
} else if piece.Name == 'p' {
} else {
}
}
return score
}
// Child-level negamax search function.
// Unlike NegaMax(), only returns score, not full move.
func NegaMaxChild(b *engine.Board, depth int) float64 {
if b.IsOver() != 0 || depth == 0 {
return EvalBoard(b)
}
var score float64 = LOSS
var childscore float64
for _, board := range b.NewGen() {
childscore = -NegaMaxChild(board, depth-1)
if childscore > score {
score = childscore
if score == WIN {
return score
}
}
}
return score
}
// Measures how many squares a piece can attack in a given direction
func AttackRay(p *engine.Piece, b *engine.Board, dir [2]int) int {
if p.Captured {
return 0
}
if !p.Infinite_direction {
return 1
}
for n := 1; n < 8; n++ {
s := &engine.Square{
X: p.Position.X + dir[0]*n,
Y: p.Position.Y + dir[1]*n,
}
if occupied, _ := b.Occupied(s); occupied != 0 {
if occupied == -2 {
return n - 1
}
return n
}
}
return 7
}
// Child level NegaScout search function.
// Unlike its parent, only returns score and not full move
func NegaScoutChild(b *engine.Board, depth int, alpha, beta float64) float64 {
if b.IsOver() != 0 || depth == 0 {
return EvalBoard(b)
}
// not indended for actual use
orderedmoves := b.AllLegalMoves()
var score float64
for i, m := range orderedmoves {
childboard := b.CopyBoard()
childboard.Move(m)
if i != 0 {
score = -NegaScoutChild(childboard, depth-1, -alpha-1, -alpha)
if alpha < score && score < beta {
score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
}
} else {
score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
}
alpha = math.Max(alpha, score)
if alpha >= beta {
break
}
}
return alpha
}
// First-level NegaScout search function.
// When called, alpha and beta should be set to the lowest and highest values possible.
func NegaScout(b *engine.Board, depth int, alpha, beta float64) *engine.Move {
if b.IsOver() != 0 || depth == 0 {
b.Lastmove.Score = EvalBoard(b)
return &b.Lastmove
}
var move engine.Move
// not indended for actual use
orderedmoves := b.AllLegalMoves()
var score float64
for i, m := range orderedmoves {
childboard := b.CopyBoard()
childboard.Move(m)
if i != 0 {
score = -NegaScoutChild(childboard, depth-1, -alpha-1, -alpha)
if alpha < score && score < beta {
score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
}
} else {
score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
}
alpha = math.Max(alpha, score)
if alpha >= beta {
move = *m.CopyMove()
move.Score = alpha
break
}
}
return &move
}
// First-level negamax search function.
func NegaMax(b *engine.Board, depth int) *engine.Move {
if b.IsOver() != 0 || depth == 0 {
b.Lastmove.Score = EvalBoard(b)
return &b.Lastmove
}
var move engine.Move
move.Score = LOSS
for _, m := range b.AllLegalMoves() {
childboard := b.CopyBoard()
childboard.Move(m)
childscore := -NegaMaxChild(childboard, depth-1)
if childscore > move.Score {
move = *m.CopyMove()
move.Score = childscore
if move.Score == WIN {
return &move
}
}
}
return &move
}
// Child level returns an evaluation
func AlphaBetaChild(b *engine.Board, depth int, alpha, beta float64, volatile bool) float64 {
var movelist []*engine.Move
if b.IsOver() != 0 {
return EvalBoard(b)
} else if depth == 0 {
if !volatile {
return EvalBoard(b)
}
depth += 1
movelist = orderedMoves(b, true)
} else {
movelist = orderedMoves(b, false)
}
var score float64
if b.Turn == 1 {
for _, move := range movelist {
b.ForceMove(move)
if !volatile && (move.Capture != 0 || b.IsCheck(b.Turn)) {
score = AlphaBetaChild(b, depth-1, alpha, beta, true)
} else {
score = AlphaBetaChild(b, depth-1, alpha, beta, false)
}
b.UndoMove(move)
if score > alpha {
alpha = score
}
if alpha >= beta {
return alpha
}
}
return alpha
} else {
for _, move := range movelist {
b.ForceMove(move)
if !volatile && (move.Capture != 0 || b.IsCheck(b.Turn)) {
score = AlphaBetaChild(b, depth-1, alpha, beta, true)
} else {
score = AlphaBetaChild(b, depth-1, alpha, beta, false)
}
b.UndoMove(move)
if score < beta {
beta = score
}
if beta <= alpha {
return beta
}
}
return beta
}
return 0
}
// Standard minmax search with alpha beta pruning.
// Initial call: alpha set to lowest value, beta set to highest.
// Top level returns a move.
func AlphaBeta(b *engine.Board, depth int, alpha, beta float64) *engine.Move {
if b.IsOver() != 0 || depth == 0 {
return nil
}
var bestmove *engine.Move = nil
var result float64
movelist := orderedMoves(b, false)
if b.Turn == 1 {
for _, move := range movelist {
b.ForceMove(move)
if move.Capture != 0 || b.IsCheck(b.Turn) {
result = AlphaBetaChild(b, depth-1, alpha, beta, true)
} else {
result = AlphaBetaChild(b, depth-1, alpha, beta, false)
}
b.UndoMove(move)
if result > alpha {
alpha = result
bestmove = move
bestmove.Score = alpha
}
if alpha >= beta {
bestmove = move
bestmove.Score = alpha
return bestmove
}
}
if bestmove == nil {
return b.AllLegalMoves()[0]
}
return bestmove
} else {
for _, move := range movelist {
b.ForceMove(move)
if move.Capture != 0 || b.IsCheck(b.Turn) {
result = AlphaBetaChild(b, depth-1, alpha, beta, true)
} else {
result = AlphaBetaChild(b, depth-1, alpha, beta, false)
}
if LOG {
fmt.Println(move.ToString(), result)
}
b.UndoMove(move)
if result < beta {
beta = result
bestmove = move
bestmove.Score = beta
}
if beta <= alpha {
bestmove = move
bestmove.Score = beta
return bestmove
}
}
if bestmove == nil {
return b.AllLegalMoves()[0]
}
return bestmove
}
if bestmove == nil {
return b.AllLegalMoves()[0]
}
return bestmove
}
// Returns the score from the point of view of the person whose turn it is.
// Positive numbers indicate a stronger position.
func EvalBoard(b *engine.Board) float64 {
if over := b.IsOver(); over != 0 {
if over == 1 {
return DRAW
} else {
if over > 0 {
return WHITEWIN
} else {
return BLACKWIN
}
}
}
attackarray := [8][8]int{}
whitepawns := []engine.Square{}
blackpawns := []engine.Square{}
var score float64
for _, piece := range b.Board {
if !piece.Captured {
score += float64(VALUES[piece.Name] * piece.Color)
updateAttackArray(b, piece, &attackarray)
if piece.Name == 'p' {
if piece.Color == 1 {
whitepawns = append(whitepawns, piece.Position)
} else {
blackpawns = append(blackpawns, piece.Position)
}
}
}
}
score += pawnStructureAnalysis(whitepawns, 1)
score -= pawnStructureAnalysis(blackpawns, -1)
whiterooks := []engine.Square{}
blackrooks := []engine.Square{}
for _, piece := range b.Board {
if !piece.Captured {
if piece.Name != 'q' && piece.Name != 'k' {
if attackarray[piece.Position.X-1][piece.Position.Y-1]*piece.Color < 1 {
score += float64(piece.Color) * HUNGPIECE
}
}
switch piece.Name {
case 'k':
if piece.Color == 1 {
score += checkKingSafety(piece.Position.X, whitepawns)
} else {
score -= checkKingSafety(piece.Position.X, blackpawns)
}
case 'p':
// reward passed pawns
if piece.Color == 1 {
if pawnIsPassed(piece, blackpawns) {
score += PASSEDPAWN
}
} else {
if pawnIsPassed(piece, whitepawns) {
score -= PASSEDPAWN
}
}
case 'n':
if piece.Position.X >= 3 && piece.Position.X <= 6 && piece.Position.Y >= 3 && piece.Position.Y <= 6 {
score += float64(piece.Color) * CENTRALKNIGHT
}
case 'b':
var numattacking int
for _, dir := range piece.Directions {
numattacking += AttackRay(piece, b, dir)
}
score += float64(piece.Color*numattacking) * BISHOPSQUARES
case 'r':
if (piece.Color == -1 && piece.Position.Y == 2) || (piece.Color == 1 && piece.Position.Y == 7) {
score += float64(piece.Color) * ROOKONSEVENTH
}
if piece.Color == 1 {
whiterooks = append(whiterooks, piece.Position)
} else {
blackrooks = append(blackrooks, piece.Position)
}
}
}
}
score += rookAnalysis(whiterooks)
score -= rookAnalysis(blackrooks)
for x := 0; x < 8; x++ {
for y := 0; y < 8; y++ {
if attackarray[x][y] > 0 {
if x >= 2 && x <= 5 && y >= 2 && y <= 5 {
score += IMPORTANTSQUARE
} else {
score += WEAKSQUARE
}
} else if attackarray[x][y] < 0 {
if x >= 2 && x <= 5 && y >= 2 && y <= 5 {
score -= IMPORTANTSQUARE
} else {
score -= WEAKSQUARE
}
}
}
}
return score
}