Threefold repetition rule

fdomig · fdomig · commit 62922d4f64db · 2016-03-22T23:48:23.000+01:00
diff --git a/engine/search.go b/engine/search.go
@@ -107,7 +107,7 @@ func (pv *pvSearch) alphaBeta(depth, alpha, beta int) int {
 	}
 
 	// repetition
-	if pv.board.ply > 0 && pv.board.repetitions() > 0 {
+	if pv.board.ply > 0 && pv.board.repetitions() >= 3 {
 		return scoreDraw
 	}
 
diff --git a/engine/search_test.go b/engine/search_test.go
@@ -0,0 +1,15 @@
+package engine
+
+import "testing"
+
+func TestBestMoveForEndgamePosition(t *testing.T) {
+
+	board := NewBoard("4k3/2R5/4p2b/4Pb1P/8/5K2/8/8 w - - 16 70")
+
+	best := Search(board)
+
+	if best.From == C7 && best.To == G7 {
+		t.Errorf("Expected best move to not be: %s", best.String())
+	}
+
+}

Original file line number	Diff line number	Diff line change
`@@ -107,7 +107,7 @@ func (pv *pvSearch) alphaBeta(depth, alpha, beta int) int {`
`107`	`107`	`}`
`108`	`108`
`109`	`109`	`// repetition`
`110`		`- if pv.board.ply > 0 && pv.board.repetitions() > 0 {`
	`110`	`+ if pv.board.ply > 0 && pv.board.repetitions() >= 3 {`
`111`	`111`	`return scoreDraw`
`112`	`112`	`}`
`113`	`113`