From 8fd34d7763072fc3ec7216729c1f7b7354bfa470 Mon Sep 17 00:00:00 2001
From: VoyagerOne <excelgeek@gmail.com>
Date: Mon, 12 Oct 2015 14:00:54 -0700
Subject: [PATCH] Combination of two ideas:

Apply bonus for the prior CMH that caused a fail low.

Balance Stats: CMH and History bonuses are updated differently.
This eliminates the "fudge" factor weight when scoring moves. Also
eliminated discontinuity in the gravity history stat formula. (i.e. stat
scores will no longer inverse when depth exceeds 22)

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 21802 W: 4107 L: 3887 D: 13808

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 46036 W: 7046 L: 6756 D: 32234

Bench: 7677367
---
 src/movepick.cpp |  2 +-
 src/movepick.h   | 18 ++++++++++++++----
 src/search.cpp   | 23 ++++++++++++++++++-----
 3 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 3d44721b..7cf3e607 100644
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -146,7 +146,7 @@ void MovePicker::score<QUIETS>() {
 
   for (auto& m : *this)
       m.value =  history[pos.moved_piece(m)][to_sq(m)]
-               + cmh[pos.moved_piece(m)][to_sq(m)] * 3;
+               + cmh[pos.moved_piece(m)][to_sq(m)];
 }
 
 template<>
diff --git a/src/movepick.h b/src/movepick.h
index e64ebfad..b488313a 100644
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -39,7 +39,7 @@
 template<typename T>
 struct Stats {
 
-  static const Value Max = Value(1 << 28);
+  static const Value Max = Value(1<<28);
 
   const T* operator[](Piece pc) const { return table[pc]; }
   T* operator[](Piece pc) { return table[pc]; }
@@ -51,10 +51,20 @@ struct Stats {
         table[pc][to] = m;
   }
 
-  void update(Piece pc, Square to, Value v) {
+  void updateH(Piece pc, Square to, Value v) {
 
-    table[pc][to] -= table[pc][to] * std::min(abs(v), 512) / 512;
-    table[pc][to] += v * 64;
+    if (abs(int(v)) >= 324) 
+        return;
+    table[pc][to] -= table[pc][to] * abs(int(v)) / 324;
+    table[pc][to] += int(v) * 32;
+  }
+
+  void updateCMH(Piece pc, Square to, Value v) {
+
+    if (abs(int(v)) >= 324) 
+        return;
+    table[pc][to] -= table[pc][to] * abs(int(v)) / 512;
+    table[pc][to] += int(v) * 64;
   }
 
 private:
diff --git a/src/search.cpp b/src/search.cpp
index efcbdef0..4988dc8e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1132,6 +1132,19 @@ moves_loop: // When in check and at SpNode search starts from here
     else if (bestMove && !pos.capture_or_promotion(bestMove))
         update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount);
 
+    // Bonus for prior countermove that caused the fail low
+    else if (!bestMove)
+    {
+        if (is_ok((ss - 2)->currentMove) && is_ok((ss - 1)->currentMove) && !pos.captured_piece_type() && !inCheck && depth>=3*ONE_PLY)
+        {
+            Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY));
+            Square prevSq = to_sq((ss - 1)->currentMove);
+            Square prevPrevSq = to_sq((ss - 2)->currentMove);
+            HistoryStats& flMoveCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
+            flMoveCmh.updateCMH(pos.piece_on(prevSq), prevSq, bonus);
+        }
+    }
+
     tte->save(posKey, value_to_tt(bestValue, ss->ply),
               bestValue >= beta ? BOUND_LOWER :
               PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
@@ -1405,21 +1418,21 @@ moves_loop: // When in check and at SpNode search starts from here
     Square prevSq = to_sq((ss-1)->currentMove);
     HistoryStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
 
-    History.update(pos.moved_piece(move), to_sq(move), bonus);
+    History.updateH(pos.moved_piece(move), to_sq(move), bonus);
 
     if (is_ok((ss-1)->currentMove))
     {
         Countermoves.update(pos.piece_on(prevSq), prevSq, move);
-        cmh.update(pos.moved_piece(move), to_sq(move), bonus);
+        cmh.updateCMH(pos.moved_piece(move), to_sq(move), bonus);
     }
 
     // Decrease all the other played quiet moves
     for (int i = 0; i < quietsCnt; ++i)
     {
-        History.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+        History.updateH(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);
+            cmh.updateCMH(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
     }
 
     // Extra penalty for PV move in previous ply when it gets refuted
@@ -1427,7 +1440,7 @@ moves_loop: // When in check and at SpNode search starts from here
     {
         Square prevPrevSq = to_sq((ss-2)->currentMove);
         HistoryStats& ttMoveCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
-        ttMoveCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * depth / ONE_PLY - 1);
+        ttMoveCmh.updateCMH(pos.piece_on(prevSq), prevSq, -bonus - 2 * depth / ONE_PLY - 1);
     }
   }
 
-- 
2.39.2