From ca4e78db8db1288eb5c8deecb9bdf402f53fdc98 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 15 Mar 2009 16:44:12 +0100
Subject: [PATCH] Revert NULL move beta corrections After testing result is bad
 -25 ELO

---
 src/evaluate.cpp | 34 ++++++++++++++++++----------------
 src/evaluate.h   |  1 -
 src/search.cpp   | 20 ++------------------
 3 files changed, 20 insertions(+), 35 deletions(-)

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 4745da02..c397671c 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -289,6 +289,7 @@ namespace {
 
   void evaluate_space(const Position &p, Color us, EvalInfo &ei);
   inline Value apply_weight(Value v, int w);
+  Value scale_by_game_phase(Value mv, Value ev, Phase ph, const ScaleFactor sf[]);
 
   int count_1s_8bit(Bitboard b);
 
@@ -527,22 +528,6 @@ void read_weights(Color us) {
 }
 
 
-/// scale_by_game_phase() interpolates between a middle game and an endgame
-/// score, based on game phase.  It also scales the return value by a
-/// ScaleFactor array.
-
-Value scale_by_game_phase(Value mv, Value ev, Phase ph, const ScaleFactor sf[]) {
-
-  assert(mv > -VALUE_INFINITE && mv < VALUE_INFINITE);
-  assert(ev > -VALUE_INFINITE && ev < VALUE_INFINITE);
-  assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);
-
-  ev = apply_scale_factor(ev, sf[(ev > Value(0) ? WHITE : BLACK)]);
-
-  Value result = Value(int((mv * ph + ev * (128 - ph)) / 128));
-  return Value(int(result) & ~(GrainSize - 1));
-}
-
 namespace {
 
   // evaluate_common() computes terms common to all pieces attack
@@ -1159,6 +1144,23 @@ namespace {
   }
 
 
+  // scale_by_game_phase() interpolates between a middle game and an endgame
+  // score, based on game phase.  It also scales the return value by a
+  // ScaleFactor array.
+
+  Value scale_by_game_phase(Value mv, Value ev, Phase ph, const ScaleFactor sf[]) {
+
+    assert(mv > -VALUE_INFINITE && mv < VALUE_INFINITE);
+    assert(ev > -VALUE_INFINITE && ev < VALUE_INFINITE);
+    assert(ph >= PHASE_ENDGAME && ph <= PHASE_MIDGAME);
+
+    ev = apply_scale_factor(ev, sf[(ev > Value(0) ? WHITE : BLACK)]);
+
+    Value result = Value(int((mv * ph + ev * (128 - ph)) / 128));
+    return Value(int(result) & ~(GrainSize - 1));
+  }
+
+
   // count_1s_8bit() counts the number of nonzero bits in the 8 least
   // significant bits of a Bitboard. This function is used by the king
   // shield evaluation.
diff --git a/src/evaluate.h b/src/evaluate.h
index 1e97fd35..b95aa15d 100644
--- a/src/evaluate.h
+++ b/src/evaluate.h
@@ -105,7 +105,6 @@ extern Value quick_evaluate(const Position &pos);
 extern void init_eval(int threads);
 extern void quit_eval();
 extern void read_weights(Color sideToMove);
-extern Value scale_by_game_phase(Value mv, Value ev, Phase ph, const ScaleFactor sf[]);
 
 
 #endif // !defined(EVALUATE_H_INCLUDED)
diff --git a/src/search.cpp b/src/search.cpp
index 92d2c75e..549f19e2 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -149,16 +149,6 @@ namespace {
   // evaluation of the position is more than NullMoveMargin below beta.
   const Value NullMoveMargin = Value(0x300);
 
-  //Null move search refutes move when Nullvalue >= Beta - Delta. Index is depth
-  //in full plies. Last index is 9+.
-  const Value NullMoveDeltaMidgame[] =
-    { Value(-8), Value( 6), Value(-15), Value( 9), Value(21),
-      Value(34), Value(54), Value( 59), Value(61), Value(61) };
-
-  const Value NullMoveDeltaEndgame[] =
-    { Value( 6), Value( 0), Value(-13), Value(-9), Value(-35),
-      Value(12), Value(24), Value(  9), Value( 5), Value(  5) };
-
   // Pruning criterions.  See the code and comments in ok_to_prune() to
   // understand their precise meaning.
   const bool PruneEscapeMoves = false;
@@ -1207,19 +1197,13 @@ namespace {
         &&  ok_to_do_nullmove(pos)
         &&  approximateEval >= beta - NullMoveMargin)
     {
-        //Calculate correct delta. Idea and tuning from Joona Kiiski.
-        ScaleFactor factor[2] = { SCALE_FACTOR_NORMAL, SCALE_FACTOR_NORMAL };
-        Phase phase = pos.game_phase();
-        int i = Min(depth / OnePly, 9);
-        Value delta = scale_by_game_phase(NullMoveDeltaMidgame[i], NullMoveDeltaEndgame[i], phase, factor);
-
         ss[ply].currentMove = MOVE_NULL;
 
         StateInfo st;
         pos.do_null_move(st);
         int R = (depth >= 4 * OnePly ? 4 : 3); // Null move dynamic reduction
 
-        Value nullValue = -search(pos, ss, -(beta-delta-1), depth-R*OnePly, ply+1, false, threadID);
+        Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
 
         pos.undo_null_move();
 
@@ -1227,7 +1211,7 @@ namespace {
         {
             /* Do not return unproven mates */
         }
-        else if (nullValue >= beta - delta)
+        else if (nullValue >= beta)
         {
             if (depth < 6 * OnePly)
                 return beta;
-- 
2.39.2