From 2097cd12217a0e18c59bd88424ca613572e6feb2 Mon Sep 17 00:00:00 2001
From: Joona Kiiski <joona.kiiski@gmail.com>
Date: Sat, 30 Mar 2013 19:49:49 +0000
Subject: [PATCH] Introduce asymmetric SEE.

No functional change
---
 src/position.cpp | 20 ++++++++++++++++++++
 src/position.h   |  2 ++
 2 files changed, 22 insertions(+)

diff --git a/src/position.cpp b/src/position.cpp
index ad699cc0..22c17173 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1148,6 +1148,16 @@ int Position::see_sign(Move m) const {
 }
 
 int Position::see(Move m) const {
+  return do_see<false>(m, 0);
+}
+
+int Position::see_asymm(Move m, int asymmThreshold) const
+{
+  return do_see<true>(m, asymmThreshold);
+}
+
+template <bool Asymmetric>
+int Position::do_see(Move m, int asymmThreshold) const {
 
   Square from, to;
   Bitboard occupied, attackers, stmAttackers;
@@ -1224,6 +1234,16 @@ int Position::see(Move m) const {
 
   } while (stmAttackers);
 
+  // FIXME: Document
+  if (Asymmetric)
+  {
+      for (int i = 0; i < slIndex ; slIndex += 2)
+      {
+          if (swapList[slIndex] < asymmThreshold)
+               swapList[slIndex] = - QueenValueMg * 16;
+      }
+  }
+
   // Having built the swap list, we negamax through it to find the best
   // achievable score from the point of view of the side to move.
   while (--slIndex)
diff --git a/src/position.h b/src/position.h
index 8d15f266..2ad9294f 100644
--- a/src/position.h
+++ b/src/position.h
@@ -160,6 +160,8 @@ public:
   // Static exchange evaluation
   int see(Move m) const;
   int see_sign(Move m) const;
+  int see_asymm(Move m, int asymmThreshold) const;
+  template <bool Asymmetric> int do_see(Move m, int asymmThreshold) const; //FIXME: private!!
 
   // Accessing hash keys
   Key key() const;
-- 
2.39.2