Introduce scale factor in pawn evaluation

[stockfish] / src / material.cpp

diff --git a/src/material.cpp b/src/material.cpp
index a3d9f7c8a73958ca7c8235e6f62c81ec85479d58..f0ee5f682d02cada44957745849684613f3e4196 100644 (file)
--- a/src/material.cpp
+++ b/src/material.cpp
@@ -1,7 +1,7 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2009 Marco Costalba
+  Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -37,10 +37,15 @@ using namespace std;
 
 namespace {
 
+  // Values modified by Joona Kiiski
+  const Value MidgameLimit = Value(15581);
+  const Value EndgameLimit = Value(3998);
+
   // Polynomial material balance parameters
   const Value RedundantQueenPenalty = Value(320);
   const Value RedundantRookPenalty  = Value(554);
-  const int LinearCoefficients[6]   = { 1617, -162, -1172, -190, 105, 26 };
+
+  const int LinearCoefficients[6] = { 1617, -162, -1172, -190, 105, 26 };
 
   const int QuadraticCoefficientsSameColor[][6] = {
   { 7, 7, 7, 7, 7, 7 }, { 39, 2, 7, 7, 7, 7 }, { 35, 271, -4, 7, 7, 7 },
@@ -129,6 +134,22 @@ MaterialInfoTable::~MaterialInfoTable() {
 }
 
 
+/// MaterialInfoTable::game_phase() calculates the phase given the current
+/// position. Because the phase is strictly a function of the material, it
+/// is stored in MaterialInfo.
+
+Phase MaterialInfoTable::game_phase(const Position& pos) {
+
+  Value npm = pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK);
+
+  if (npm >= MidgameLimit)
+      return PHASE_MIDGAME;
+  else if (npm <= EndgameLimit)
+      return PHASE_ENDGAME;
+
+  return Phase(((npm - EndgameLimit) * 128) / (MidgameLimit - EndgameLimit));
+}
+
 /// MaterialInfoTable::get_material_info() takes a position object as input,
 /// computes or looks up a MaterialInfo object, and returns a pointer to it.
 /// If the material configuration is not already present in the table, it
@@ -151,6 +172,9 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
   mi->clear();
   mi->key = key;
 
+  // Store game phase
+  mi->gamePhase = MaterialInfoTable::game_phase(pos);
+
   // Let's look if we have a specialized evaluation function for this
   // particular material configuration. First we look for a fixed
   // configuration one, then a generic one if previous search failed.
@@ -269,8 +293,8 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
                                  { pos.piece_count(BLACK, BISHOP) > 1, pos.piece_count(BLACK, PAWN), pos.piece_count(BLACK, KNIGHT),
                                    pos.piece_count(BLACK, BISHOP), pos.piece_count(BLACK, ROOK), pos.piece_count(BLACK, QUEEN) } };
   Color c, them;
-  int sign;
-  int matValue = 0;
+  int sign, pt1, pt2, pc;
+  int v, vv, matValue = 0;
 
   for (c = WHITE, sign = 1; c <= BLACK; c++, sign = -sign)
   {
@@ -280,7 +304,7 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
     {
         if (   pos.non_pawn_material(c) == pos.non_pawn_material(opposite_color(c))
             || pos.non_pawn_material(c) < RookValueMidgame)
-            mi->factor[c] = 0;
+            mi->factor[c] = SCALE_FACTOR_ZERO;
         else
         {
             switch (pos.piece_count(c, BISHOP)) {
@@ -304,25 +328,27 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
         matValue -= sign * ((pieceCount[c][ROOK] - 1) * RedundantRookPenalty + pieceCount[c][QUEEN] * RedundantQueenPenalty);
 
     them = opposite_color(c);
+    v = 0;
 
     // Second-degree polynomial material imbalance by Tord Romstad
     //
     // We use NO_PIECE_TYPE as a place holder for the bishop pair "extended piece",
     // this allow us to be more flexible in defining bishop pair bonuses.
-    for (int pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
+    for (pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
     {
-        int c1 = sign * pieceCount[c][pt1];
-        if (!c1)
+        pc = pieceCount[c][pt1];
+        if (!pc)
             continue;
 
-        matValue += c1 * LinearCoefficients[pt1];
+        vv = LinearCoefficients[pt1];
 
-        for (int pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
-        {
-            matValue += c1 * pieceCount[c][pt2] * QuadraticCoefficientsSameColor[pt1][pt2];
-            matValue += c1 * pieceCount[them][pt2] * QuadraticCoefficientsOppositeColor[pt1][pt2];
-        }
+        for (pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
+            vv +=  pieceCount[c][pt2] * QuadraticCoefficientsSameColor[pt1][pt2]
+                 + pieceCount[them][pt2] * QuadraticCoefficientsOppositeColor[pt1][pt2];
+
+        v += pc * vv;
     }
+    matValue += sign * v;
   }
   mi->value = int16_t(matValue / 16);
   return mi;
@@ -348,7 +374,6 @@ EndgameFunctions::EndgameFunctions() {
   add<ScalingFunction<KBPPKB>  >("KBPPKB");
   add<ScalingFunction<KBPKN>   >("KBPKN");
   add<ScalingFunction<KRPPKRP> >("KRPPKRP");
-  add<ScalingFunction<KRPPKRP> >("KRPPKRP");
 }
 
 EndgameFunctions::~EndgameFunctions() {