From 0734b1fa82b9d50181e3d0a1c327d6c2673c6506 Mon Sep 17 00:00:00 2001
From: Calcitem <calcitem@outlook.com>
Date: Sun, 10 Jan 2021 21:08:01 +0800
Subject: [PATCH] repetition: refactor: Add has_repeated() and has_game_cycle()

---
 src/position.cpp | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/position.h   |  4 ++++
 src/search.cpp   | 38 +++++---------------------------------
 3 files changed, 57 insertions(+), 33 deletions(-)

diff --git a/src/position.cpp b/src/position.cpp
index b3b8428d..97215c56 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -475,6 +475,54 @@ out:
 }
 
 
+#ifdef THREEFOLD_REPETITION
+// Position::has_repeated() tests whether there has been at least one repetition
+// of positions since the last remove.
+
+bool Position::has_repeated(Sanmill::Stack<Position> &ss) const
+{
+    for (int i = (int)posKeyHistory.size() - 2; i >= 0; i--) {
+        if (key() == posKeyHistory[i]) {
+            return true;
+        }
+    }
+
+    int size = ss.size();
+
+    for (int i = size - 1; i >= 0; i--) {
+        if (type_of(ss[i].move) == MOVETYPE_REMOVE) {
+            break;
+        }
+        if (key() == ss[i].st.key) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+
+/// Position::has_game_cycle() tests if the position has a move which draws by repetition.
+
+int repetition;
+
+bool Position::has_game_cycle() const
+{
+    for (auto i : posKeyHistory) {
+        if (key() == i) {
+            repetition++;
+            if (repetition == 3) {
+                repetition = 0;
+                return true;
+            }
+        }
+    }
+
+    return false;
+}
+#endif // THREEFOLD_REPETITION
+
+
 /// Mill Game
 
 #ifdef THREEFOLD_REPETITION
diff --git a/src/position.h b/src/position.h
index f143c945..8e40385c 100644
--- a/src/position.h
+++ b/src/position.h
@@ -90,6 +90,10 @@ public:
     Color side_to_move() const;
     int game_ply() const;
     Thread *this_thread() const;
+#ifdef THREEFOLD_REPETITION
+    bool has_game_cycle() const;
+    bool has_repeated(Sanmill::Stack<Position> &ss) const;
+#endif // THREEFOLD_REPETITION
     int rule50_count() const;
 
 
diff --git a/src/search.cpp b/src/search.cpp
index e1229ae8..136e0358 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -66,9 +66,6 @@ void Search::clear()
     Threads.clear();
 }
 
-#ifdef THREEFOLD_REPETITION
-int repetition;
-#endif // THREEFOLD_REPETITION
 
 /// Thread::search() is the main iterative deepening loop. It calls search()
 /// repeatedly with increasing depth until the allocated thinking time has been
@@ -97,21 +94,12 @@ int Thread::search()
 
 #ifdef THREEFOLD_REPETITION
     if (rootPos->get_phase() == Phase::moving) {
-        const Key key = rootPos->key();
-
-        for (auto i : posKeyHistory) {
-            if (key == i)
-            {
-                repetition++;
-                if (repetition == 3) {
-                    repetition = 0;
-                    return 3;
-                }
-            }
+        if (rootPos->has_game_cycle()) {
+            return 3;
         }
 
 #if defined(UCI_DO_BEST_MOVE) || defined(QT_GUI_LIB)
-        posKeyHistory.push_back(key);
+        posKeyHistory.push_back(rootPos->key());
 #endif // UCI_DO_BEST_MOVE
 
         assert(posKeyHistory.size() < 256);
@@ -319,24 +307,8 @@ Value search(Position *pos, Sanmill::Stack<Position> &ss, Depth depth, Depth ori
     // to pick a move and can't simply return VALUE_DRAW) then check to
     // see if the position is a repeat. if so, we can assume that
     // this line is a draw and return VALUE_DRAW.
-
-    if (depth != originDepth) {
-        for (int i = (int)posKeyHistory.size() - 2; i >= 0; i--) {
-            if (posKey == posKeyHistory[i]) {
-                return VALUE_DRAW;
-            }
-        }
-
-        int size = ss.size();
-
-        for (int i = size - 1; i >= 0; i--) {
-            if (type_of(ss[i].move) == MOVETYPE_REMOVE) {
-                break;
-            }
-            if (posKey == ss[i].st.key) {
-                return VALUE_DRAW;
-            }
-        }
+    if (depth != originDepth && pos->has_repeated(ss)) {
+        return VALUE_DRAW;
     }
 #endif // THREEFOLD_REPETITION