Add mobility evaluation

Author: ArcticXWolf

README.md

@@ -37,7 +37,8 @@ implemented.
     * Tempo evaluation
     * Pair bonus
     * Rook on (half-)open files bonus
-    * Passed pawn bonus
+    * Passed pawn evaluation
+    * Mobility evaluation
 * Simple search algorithm using
     * Negamax with alpha-beta-pruning
     * Quiescence search
@@ -62,6 +63,7 @@ implemented.
 * [chess-ai](https://github.com/xtreemtg/Chess_AI)
 * [sunfish](https://github.com/thomasahle/sunfish)
 * [Adam Berent Blog](https://adamberent.com/2019/03/02/chess-board-evaluation/)
+* [Dragontooth](https://github.com/dylhunn/dragontooth)
 * [Dragontoothmg](https://github.com/dylhunn/dragontoothmg)
 * [CounterGo](https://github.com/ChizhovVadim/CounterGo)
 * Several blogposts/stackoverflow questions found via Google

evaluation/evaluation.go

@@ -18,6 +18,7 @@ type EvaluationPart struct {
 	BlockedPiecesModifier   int
 	KingShieldModifier      int
 	PassedPawnModifier      int
+	MobilityModifier        int
 }
 
 type Evaluation struct {
@@ -86,6 +87,8 @@ func (e *Evaluation) updateTotal() {
 	e.TotalScore -= e.Black.KingShieldModifier
 	e.TotalScore += e.White.PassedPawnModifier
 	e.TotalScore -= e.Black.PassedPawnModifier
+	e.TotalScore += e.White.MobilityModifier
+	e.TotalScore -= e.Black.MobilityModifier
 
 	e.TotalScorePerspective = e.TotalScore
 	if !e.Game.Position.Wtomove {
@@ -104,6 +107,7 @@ func calculateEvaluationPart(g *game.Game, color game.PlayerColor) EvaluationPar
 		TempoModifier:           calculateTempoModifier(g, color),
 		RookFileModifier:        calculateRookModifier(g, color),
 		PassedPawnModifier:      calculatePassedPawns(g, color),
+		MobilityModifier:        calculateMobilityModifier(g, color),
 	}
 	return evalPart
 }
@@ -160,6 +164,8 @@ func getBitboardByPieceType(bbs *dragontoothmg.Bitboards, pieceType dragontoothm
 func calculateMaterialScoreForPieceType(g *game.Game, color game.PlayerColor, pieceType dragontoothmg.Piece, bitboard uint64) (int, int, int) {
 	var x uint64
 	ps, pstMid, pstEnd := 0, 0, 0
+
+	// Thanks to https://github.com/dylhunn/dragontooth for the extract pieces from bitboard pattern
 	for x = bitboard; x != 0; x &= x - 1 {
 		square := bits.TrailingZeros64(x)
 
@@ -242,3 +248,43 @@ func calculatePassedPawns(g *game.Game, color game.PlayerColor) (result int) {
 	}
 	return
 }
+
+func calculateMobilityModifier(g *game.Game, color game.PlayerColor) (result int) {
+	return calculateDiagonalMobilityModifier(g, color) + calculateLinearMobilityModifier(g, color)
+}
+
+func calculateDiagonalMobilityModifier(g *game.Game, color game.PlayerColor) (result int) {
+	diagonalBB := g.Position.White.Bishops | g.Position.White.Queens
+	ownBB := g.Position.White.All
+	if color == game.Black {
+		diagonalBB = g.Position.Black.Bishops | g.Position.Black.Queens
+		ownBB = g.Position.Black.All
+	}
+	allBB := g.Position.White.All | g.Position.Black.All
+
+	for x := diagonalBB; x != 0; x &= x - 1 {
+		square := bits.TrailingZeros64(x)
+		movableSquares := dragontoothmg.CalculateBishopMoveBitboard(uint8(square), allBB) & ^ownBB
+		result += bits.OnesCount64(movableSquares) * weights[color].AdditionalModifier.DiagonalMobilityModifier
+	}
+
+	return
+}
+
+func calculateLinearMobilityModifier(g *game.Game, color game.PlayerColor) (result int) {
+	linearBB := g.Position.White.Rooks | g.Position.White.Queens
+	ownBB := g.Position.White.All
+	if color == game.Black {
+		linearBB = g.Position.Black.Rooks | g.Position.Black.Queens
+		ownBB = g.Position.Black.All
+	}
+	allBB := g.Position.White.All | g.Position.Black.All
+
+	for x := linearBB; x != 0; x &= x - 1 {
+		square := bits.TrailingZeros64(x)
+		movableSquares := dragontoothmg.CalculateRookMoveBitboard(uint8(square), allBB) & ^ownBB
+		result += bits.OnesCount64(movableSquares) * weights[color].AdditionalModifier.LinearMobilityModifier
+	}
+
+	return
+}

evaluation/evaluation_test.go

@@ -305,3 +305,27 @@ func Test_calculatePassedPawns(t *testing.T) {
 		})
 	}
 }
+
+func Test_calculateMobilityModifier(t *testing.T) {
+	type args struct {
+		g     *game.Game
+		color game.PlayerColor
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{"GameStart White", args{game.NewFromFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"), game.White}, 0},
+		{"GameStart Black", args{game.NewFromFen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"), game.Black}, 0},
+		{"OpenBishop White", args{game.NewFromFen("rnbqkbnr/pppppppp/8/8/6P1/8/PPPPPP1P/RNBQKBNR b KQkq - 0 1"), game.White}, 4},
+		{"OpenRook Black", args{game.NewFromFen("rnbqkbnr/ppppppp1/8/7p/6P1/8/PPPPPP1P/RNBQKBNR w KQkq - 0 2"), game.Black}, 8},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := calculateMobilityModifier(tt.args.g, tt.args.color); got != tt.want {
+				t.Errorf("calculateMobilityModifier() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

evaluation/weights.go

@@ -15,6 +15,8 @@ type AdditionalModifier struct {
 	KingShieldRank2Modifier   int
 	KingShieldRank3Modifier   int
 	RookBlockedByKingModifier int
+	DiagonalMobilityModifier  int
+	LinearMobilityModifier    int
 }
 
 type GamephaseWeights struct {
@@ -40,6 +42,8 @@ var (
 		KingShieldRank2Modifier:   10,
 		KingShieldRank3Modifier:   5,
 		RookBlockedByKingModifier: 24,
+		DiagonalMobilityModifier:  2,
+		LinearMobilityModifier:    4,
 	}
 	weightsForAllPhases = GamephaseWeights{
 		Material: map[dragontoothmg.Piece]int{

search/search_test.go

@@ -106,8 +106,9 @@ func TestSearch_SearchBestMove(t *testing.T) {
 		{"Mate in 1 - White", fields{game.NewFromFen("4k3/pp3p1p/3Kp3/3P2r1/2r5/3q4/5PPP/4b2R b - - 5 29"), 3, 2}, []dragontoothmg.Move{getMove("c4c6")}, []dragontoothmg.Move{0}},
 		{"Avoid Nullmove from Issue #2", fields{game.NewFromFen("1r4k1/2p4p/B5pP/P2p1p2/3PpP2/1nP1PnQP/q5K1/B1R5 w - - 1 40"), 3, 2}, []dragontoothmg.Move{}, []dragontoothmg.Move{0}},
 		{"Mate in 1 from Issue #2", fields{game.NewFromFen("2rq1rk1/1Rp3pp/p2pN3/3Nn3/b3pb1P/2B3Q1/2PP1PP1/1R4K1 w - - 0 23"), 3, 2}, []dragontoothmg.Move{getMove("g3g7")}, []dragontoothmg.Move{0}},
-		{"Avoid mate in 1 from https://lichess.org/9FeZycDP/black#65", fields{game.NewFromFen("1r3k1R/5p2/5p2/4rQ2/p3p3/n1b3P1/4qP1P/5RK1 b - - 4 33"), 6, 3}, []dragontoothmg.Move{}, []dragontoothmg.Move{0, getMove("f8g7")}},
+		{"Avoid mate in 1 from https://lichess.org/9FeZycDP/black#65", fields{game.NewFromFen("1r3k1R/5p2/5p2/4rQ2/p3p3/n1b3P1/4qP1P/5RK1 b - - 4 33"), 3, 3}, []dragontoothmg.Move{}, []dragontoothmg.Move{0, getMove("f8g7")}},
 		{"Avoid mate in 1 from #6", fields{game.NewFromFen("3r2k1/rp1n3p/2pb2p1/p1n3P1/2PBP3/P1N3q1/1PQ1B3/3R1R1K w - - 4 35"), 3, 3}, []dragontoothmg.Move{}, []dragontoothmg.Move{0, getMove("d4f2")}},
+		{"Avoid queen loss in 2 from #8", fields{game.NewFromFen("r2r3k/3q3p/1RnN2pB/2P1pp1n/P7/6P1/Q3PP1P/6K1 b - - 0 28"), 5, 3}, []dragontoothmg.Move{getMove("a8a7")}, []dragontoothmg.Move{}},
 	}
 	logger := log.New(os.Stdout, "", log.LstdFlags)
 	evaluator := evaluation.Evaluation{}