Add followup moves history for move ordering

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 7955 W: 1538 L: 1378 D: 5039

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 5323 W: 778 L: 642 D: 3903

Bench: 8261839

Resolves #599

src/movepick.cpp

@@ -68,8 +68,8 @@ namespace {
 /// ordering is at the current node.
 
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h,
-                       const CounterMoveStats& cmh, Move cm, Search::Stack* s)
-           : pos(p), history(h), counterMoveHistory(&cmh), ss(s), countermove(cm), depth(d) {
+                       const CounterMoveStats& cmh, const CounterMoveStats& fmh, Move cm, Search::Stack* s)
+           : pos(p), history(h), counterMoveHistory(&cmh), followupMoveHistory(&fmh), ss(s), countermove(cm), depth(d) {
 
   assert(d > DEPTH_ZERO);
 
@@ -80,7 +80,7 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats&
 
 MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
                        const HistoryStats& h, Square s)
-           : pos(p), history(h), counterMoveHistory(nullptr) {
+           : pos(p), history(h), counterMoveHistory(nullptr), followupMoveHistory(nullptr) {
 
   assert(d <= DEPTH_ZERO);
 
@@ -105,7 +105,7 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
 }
 
 MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, Value th)
-           : pos(p), history(h), counterMoveHistory(nullptr), threshold(th) {
+           : pos(p), history(h), counterMoveHistory(nullptr), followupMoveHistory(nullptr), threshold(th) {
 
   assert(!pos.checkers());
 
@@ -142,7 +142,8 @@ void MovePicker::score<QUIETS>() {
 
   for (auto& m : *this)
       m.value =  history[pos.moved_piece(m)][to_sq(m)]
-               + (*counterMoveHistory)[pos.moved_piece(m)][to_sq(m)];
+               + (*counterMoveHistory)[pos.moved_piece(m)][to_sq(m)]
+               + (*followupMoveHistory)[pos.moved_piece(m)][to_sq(m)];
 }
 
 template<>

src/movepick.h

@@ -85,7 +85,7 @@ class MovePicker {
 
   MovePicker(const Position&, Move, Depth, const HistoryStats&, Square);
   MovePicker(const Position&, Move, const HistoryStats&, Value);
-  MovePicker(const Position&, Move, Depth, const HistoryStats&, const CounterMoveStats&, Move, Search::Stack*);
+  MovePicker(const Position&, Move, Depth, const HistoryStats&, const CounterMoveStats&, const CounterMoveStats&, Move, Search::Stack*);
 
   Move next_move();
 
@@ -98,6 +98,7 @@ class MovePicker {
   const Position& pos;
   const HistoryStats& history;
   const CounterMoveStats* counterMoveHistory;
+  const CounterMoveStats* followupMoveHistory;
   Search::Stack* ss;
   Move countermove;
   Depth depth;

src/search.cpp

@@ -870,10 +870,12 @@ namespace {
 moves_loop: // When in check search starts from here
 
     Square prevSq = to_sq((ss-1)->currentMove);
+    Square ownPrevSq = to_sq((ss-2)->currentMove);
     Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
     const CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq];
+    const CounterMoveStats& fmh = CounterMoveHistory[pos.piece_on(ownPrevSq)][ownPrevSq];
 
-    MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss);
+    MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, fmh, cm, ss);
     CheckInfo ci(pos);
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     improving =   ss->staticEval >= (ss-2)->staticEval
@@ -1442,7 +1444,9 @@ namespace {
     Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
 
     Square prevSq = to_sq((ss-1)->currentMove);
+    Square ownPrevSq = to_sq((ss-2)->currentMove);
     CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq];
+    CounterMoveStats& fmh = CounterMoveHistory[pos.piece_on(ownPrevSq)][ownPrevSq];
     Thread* thisThread = pos.this_thread();
 
     thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
@@ -1453,13 +1457,19 @@ namespace {
         cmh.update(pos.moved_piece(move), to_sq(move), bonus);
     }
 
+    if (is_ok((ss-2)->currentMove))
+        fmh.update(pos.moved_piece(move), to_sq(move), bonus);
+
     // Decrease all the other played quiet moves
     for (int i = 0; i < quietsCnt; ++i)
     {
         thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
 
         if (is_ok((ss-1)->currentMove))
             cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+
+        if (is_ok((ss-2)->currentMove))
+            fmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
     }
 
     // Extra penalty for a quiet TT move in previous ply when it gets refuted