From 4b703b142946ae03f03ca75738d927fd44a69b39 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Tue, 9 Jul 2013 08:01:51 +0200
Subject: [PATCH] Revert previous patch

Unfortunatly a reverse test at long TC failed:

master^ vs master
LLR: 1.37 (-2.94,2.94)
Total: 33682 W: 6294 L: 6071 D: 21317

So becuase short TC score is 50% there is a good
possibility patch is not scalable.

So revert it.

bench: 4507288
---
 src/search.cpp | 53 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 4 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index f24f33b9..220fff5e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -100,6 +100,7 @@ namespace {
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);
   bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta);
+  bool allows(const Position& pos, Move first, Move second);
   bool refutes(const Position& pos, Move first, Move second);
   string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
 
@@ -689,15 +690,18 @@ namespace {
         else
         {
             // The null move failed low, which means that we may be faced with
-            // some kind of threat. If the previous move was reduced return a fail
+            // some kind of threat. If the previous move was reduced, check if
+            // the move that refuted the null move was somehow connected to the
+            // move which was reduced. If a connection is found, return a fail
             // low score (which will cause the reduced move to fail high in the
             // parent node, which will trigger a re-search with full depth).
+            threatMove = (ss+1)->currentMove;
+
             if (   depth < 5 * ONE_PLY
                 && (ss-1)->reduction
-                && nullValue < beta - Value(128))
+                && threatMove != MOVE_NONE
+                && allows(pos, (ss-1)->currentMove, threatMove))
                 return alpha;
-
-            threatMove = (ss+1)->currentMove;
         }
     }
 
@@ -1373,6 +1377,47 @@ split_point_start: // At split points actual search starts from here
   }
 
 
+  // allows() tests whether the 'first' move at previous ply somehow makes the
+  // 'second' move possible, for instance if the moving piece is the same in
+  // both moves. Normally the second move is the threat (the best move returned
+  // from a null search that fails low).
+
+  bool allows(const Position& pos, Move first, Move second) {
+
+    assert(is_ok(first));
+    assert(is_ok(second));
+    assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
+    assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
+
+    Square m1from = from_sq(first);
+    Square m2from = from_sq(second);
+    Square m1to = to_sq(first);
+    Square m2to = to_sq(second);
+
+    // The piece is the same or second's destination was vacated by the first move
+    if (m1to == m2from || m2to == m1from)
+        return true;
+
+    // Second one moves through the square vacated by first one
+    if (between_bb(m2from, m2to) & m1from)
+      return true;
+
+    // Second's destination is defended by the first move's piece
+    Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
+    if (m1att & m2to)
+        return true;
+
+    // Second move gives a discovered check through the first's checking piece
+    if (m1att & pos.king_square(pos.side_to_move()))
+    {
+        assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
+        return true;
+    }
+
+    return false;
+  }
+
+
   // refutes() tests whether a 'first' move is able to defend against a 'second'
   // opponent's move. In this case will not be pruned. Normally the second move
   // is the threat (the best move returned from a null search that fails low).
-- 
2.39.2