From c9f9262a499131ed169035f0faa943fed3ece153 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Fri, 5 Oct 2012 08:23:56 +0200
Subject: [PATCH] Add experimental contempt factor

This is very crude and very basic: simply in case
of a draw for repetition or 50 moves rule return
a negative score instead of zero according to the
contempt factor (in centipawns). If contempt is
positive engine will try to avoid draws (to use
with weaker opponents), if negative engine will
try to draw. If zero (default) there are no changes.

No functional change.
---
 src/evaluate.cpp  | 3 +++
 src/evaluate.h    | 1 +
 src/search.cpp    | 4 ++--
 src/ucioption.cpp | 1 +
 4 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index b5b51d2c..fdfacc10 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -268,6 +268,7 @@ namespace {
 namespace Eval {
 
   Color RootColor;
+  Value ValueDrawContempt;
 
   /// evaluate() is the main evaluation function. It always computes two
   /// values, an endgame score and a middle game score, and interpolates
@@ -307,6 +308,8 @@ namespace Eval {
         KingDangerTable[1][i] = apply_weight(make_score(t, 0), Weights[KingDangerUs]);
         KingDangerTable[0][i] = apply_weight(make_score(t, 0), Weights[KingDangerThem]);
     }
+
+    ValueDrawContempt = VALUE_DRAW - Options["Contempt Factor"] * PawnValueMg / 100;
   }
 
 
diff --git a/src/evaluate.h b/src/evaluate.h
index a0418b79..9c2b2a61 100644
--- a/src/evaluate.h
+++ b/src/evaluate.h
@@ -27,6 +27,7 @@ class Position;
 namespace Eval {
 
 extern Color RootColor;
+extern Value ValueDrawContempt;
 
 extern void init();
 extern Value evaluate(const Position& pos, Value& margin);
diff --git a/src/search.cpp b/src/search.cpp
index 31edcc2f..77300708 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -546,7 +546,7 @@ namespace {
     {
         // Step 2. Check for aborted search and immediate draw
         if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
-            return VALUE_DRAW;
+            return Eval::ValueDrawContempt;
 
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
         // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
@@ -1101,7 +1101,7 @@ split_point_start: // At split points actual search starts from here
 
     // Check for an instant draw or maximum ply reached
     if (pos.is_draw<true>() || ss->ply > MAX_PLY)
-        return VALUE_DRAW;
+        return Eval::ValueDrawContempt;
 
     // Decide whether or not to include checks, this fixes also the type of
     // TT entry depth that we are going to use. Note that in qsearch we use
diff --git a/src/ucioption.cpp b/src/ucioption.cpp
index bbbbbbf9..1cdd4f2b 100644
--- a/src/ucioption.cpp
+++ b/src/ucioption.cpp
@@ -64,6 +64,7 @@ void init(OptionsMap& o) {
   o["Search Log Filename"]         = Option("SearchLog.txt");
   o["Book File"]                   = Option("book.bin");
   o["Best Book Move"]              = Option(false);
+  o["Contempt Factor"]             = Option(0, -50,  50, on_eval);
   o["Mobility (Middle Game)"]      = Option(100, 0, 200, on_eval);
   o["Mobility (Endgame)"]          = Option(100, 0, 200, on_eval);
   o["Passed Pawns (Middle Game)"]  = Option(100, 0, 200, on_eval);
-- 
2.39.2