From 4f4c1c75e743b95ba4e5062d46fcd7af106ccec6 Mon Sep 17 00:00:00 2001
From: Peter Osterlund <peterosterlund2@gmail.com>
Date: Sun, 4 Mar 2012 19:00:09 +0000
Subject: [PATCH] CuckooChess: Don't use LMP when alpha or beta is a mate
 score.

---
 CuckooChessEngine/src/chess/Evaluate.java    |  1 +
 CuckooChessEngine/src/chess/Player.java      |  2 +-
 CuckooChessEngine/src/chess/Search.java      | 18 ++++++++++--------
 CuckooChessEngine/src/chess/TextIO.java      |  2 +-
 CuckooChessEngine/test/chess/SearchTest.java | 15 +++++++++++++--
 5 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/CuckooChessEngine/src/chess/Evaluate.java b/CuckooChessEngine/src/chess/Evaluate.java
index eec2bcd..c553021 100644
--- a/CuckooChessEngine/src/chess/Evaluate.java
+++ b/CuckooChessEngine/src/chess/Evaluate.java
@@ -756,6 +756,7 @@ public class Evaluate {
     }
 
     private int threatBonus(Position pos) {
+        // FIXME!! Try higher weight for attacks on more valuable pieces.
         int score = 0;
 
         // Sum values for all black pieces under attack
diff --git a/CuckooChessEngine/src/chess/Player.java b/CuckooChessEngine/src/chess/Player.java
index 4b24aee..0530f51 100644
--- a/CuckooChessEngine/src/chess/Player.java
+++ b/CuckooChessEngine/src/chess/Player.java
@@ -53,7 +53,7 @@ public interface Player {
 
     /** 
      * Inform player that the transposition table should be cleared.
-     * Of coarse, a human player has a hard time implementing this.
+     * Of course, a human player has a hard time implementing this.
      */
     public void clearTT();
 }
diff --git a/CuckooChessEngine/src/chess/Search.java b/CuckooChessEngine/src/chess/Search.java
index 62f4eaf..9770cb9 100644
--- a/CuckooChessEngine/src/chess/Search.java
+++ b/CuckooChessEngine/src/chess/Search.java
@@ -734,14 +734,16 @@ public class Search {
             boolean givesCheck = MoveGen.givesCheck(pos, m); 
             boolean doFutility = false;
             if (mayReduce && haveLegalMoves && !givesCheck && !passedPawnPush(pos, m)) {
-                int moveCountLimit;
-                if (depth <= plyScale)          moveCountLimit = 3;
-                else if (depth <= 2 * plyScale) moveCountLimit = 6;
-                else if (depth <= 3 * plyScale) moveCountLimit = 12;
-                else if (depth <= 4 * plyScale) moveCountLimit = 24;
-                else moveCountLimit = 256;
-                if (mi >= moveCountLimit)
-                    continue; // Late move pruning
+                if ((Math.abs(alpha) <= MATE0 / 2) && (Math.abs(beta) <= MATE0 / 2)) {
+                    int moveCountLimit;
+                    if (depth <= plyScale)          moveCountLimit = 3;
+                    else if (depth <= 2 * plyScale) moveCountLimit = 6;
+                    else if (depth <= 3 * plyScale) moveCountLimit = 12;
+                    else if (depth <= 4 * plyScale) moveCountLimit = 24;
+                    else moveCountLimit = 256;
+                    if (mi >= moveCountLimit)
+                        continue; // Late move pruning
+                }
                 if (futilityPrune)
                     doFutility = true;
             }
diff --git a/CuckooChessEngine/src/chess/TextIO.java b/CuckooChessEngine/src/chess/TextIO.java
index 402856d..9283314 100644
--- a/CuckooChessEngine/src/chess/TextIO.java
+++ b/CuckooChessEngine/src/chess/TextIO.java
@@ -290,7 +290,7 @@ public class TextIO {
                 ret.append("O-O-O");
             }
         } else if (move.from == bKingOrigPos && pos.getPiece(bKingOrigPos) == Piece.BKING) {
-            // Check white castle
+            // Check black castle
             if (move.to == Position.getSquare(6, 7)) {
                 ret.append("O-O");
             } else if (move.to == Position.getSquare(2, 7)) {
diff --git a/CuckooChessEngine/test/chess/SearchTest.java b/CuckooChessEngine/test/chess/SearchTest.java
index 244776b..45bbf96 100644
--- a/CuckooChessEngine/test/chess/SearchTest.java
+++ b/CuckooChessEngine/test/chess/SearchTest.java
@@ -204,7 +204,18 @@ public class SearchTest {
         Move bestM = idSearch(sc, 28);
         assertEquals(TextIO.stringToMove(pos, "Kb1"), new Move(bestM));
     }
-    
+
+    /**
+     * Late move pruning must not be used in mate search.
+     */
+    @Test
+    public void testLMP() throws ChessParseError {
+        Position pos = TextIO.readFEN("2r2rk1/6p1/p3pq1p/1p1b1p2/3P1n2/PP3N2/3N1PPP/1Q2RR1K b");  // WAC 174
+        Search sc = new Search(pos, nullHist, 0, tt);
+        Move bestM = idSearch(sc, 2);
+        assertTrue(bestM.score < Search.MATE0 / 2);
+    }
+
     @Test
     public void testCheckEvasion() throws ChessParseError {
         System.out.println("check evasion");
@@ -234,7 +245,7 @@ public class SearchTest {
         System.out.println("kqkrNullMove");
         Position pos = TextIO.readFEN("7K/6R1/5k2/3q4/8/8/8/8 b - - 0 1");
         Search sc = new Search(pos, nullHist, 0, tt);
-        Move bestM = idSearch(sc, 9);
+        Move bestM = idSearch(sc, 10);
         assertEquals(Search.MATE0-18, bestM.score);
     }