From 1588a4e84695e48e47c5c8b83d14ead285530c45 Mon Sep 17 00:00:00 2001
From: Tord Romstad <tord@cm-84.215.101.133.getinternet.no>
Date: Sun, 24 Jan 2010 16:09:32 +0100
Subject: [PATCH] Fixes a Chess960 bug when playing with more than one search
 thread.

The init_eval() function corrupted the static array castleRightsMask[]
in the Position class, resulting in instant crashes in most Chess960
games. Fixed by repairing the damage directly after the function is
called. Also modified the Position::to_fen() function to display
castle rights correctly for Chess960 positions, and added sanity checks
for uncastled rook files in Position::is_ok().
---
 src/position.cpp | 42 ++++++++++++++++++++++++++++++++++++++----
 src/search.cpp   |  4 ++++
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/src/position.cpp b/src/position.cpp
index fb17f209..7ee63b22 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -271,10 +271,24 @@ const string Position::to_fen() const {
   fen += (sideToMove == WHITE ? "w " : "b ");
   if (st->castleRights != NO_CASTLES)
   {
-    if (can_castle_kingside(WHITE))  fen += 'K';
-    if (can_castle_queenside(WHITE)) fen += 'Q';
-    if (can_castle_kingside(BLACK))  fen += 'k';
-    if (can_castle_queenside(BLACK)) fen += 'q';
+     if (initialKFile == FILE_E && initialQRFile == FILE_A && initialKRFile == FILE_H)
+     {
+        if (can_castle_kingside(WHITE))  fen += 'K';
+        if (can_castle_queenside(WHITE)) fen += 'Q';
+        if (can_castle_kingside(BLACK))  fen += 'k';
+        if (can_castle_queenside(BLACK)) fen += 'q';
+     } 
+     else
+     {
+        if (can_castle_kingside(WHITE)) 
+           fen += toupper(file_to_char(initialKRFile));
+        if (can_castle_queenside(WHITE)) 
+           fen += toupper(file_to_char(initialQRFile));
+        if (can_castle_kingside(BLACK)) 
+           fen += file_to_char(initialKRFile);
+        if (can_castle_queenside(BLACK)) 
+           fen += file_to_char(initialQRFile);
+     }
   } else
       fen += '-';
 
@@ -1850,6 +1864,7 @@ bool Position::is_ok(int* failedStep) const {
   static const bool debugNonPawnMaterial = false;
   static const bool debugPieceCounts = false;
   static const bool debugPieceList = false;
+  static const bool debugCastleSquares = false;
 
   if (failedStep) *failedStep = 1;
 
@@ -1986,6 +2001,25 @@ bool Position::is_ok(int* failedStep) const {
                       return false;
               }
   }
+
+  if (failedStep) (*failedStep)++;
+  if (debugCastleSquares) {
+     for (Color c = WHITE; c <= BLACK; c++) {
+        if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != piece_of_color_and_type(c, ROOK))
+           return false;
+        if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != piece_of_color_and_type(c, ROOK))
+           return false;
+     }
+     if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
+        return false;
+     if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
+        return false;
+     if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
+        return false;
+     if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
+        return false;
+  }
+
   if (failedStep) *failedStep = 0;
   return true;
 }
diff --git a/src/search.cpp b/src/search.cpp
index 65c29bf3..71b974b6 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -442,6 +442,10 @@ bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
   {
       ActiveThreads = newActiveThreads;
       init_eval(ActiveThreads);
+      // HACK: init_eval() destroys the static castleRightsMask[] array in the
+      // Position class. The below line repairs the damage.
+      Position p(pos.to_fen());
+      assert(pos.is_ok());
   }
 
   // Wake up sleeping threads
-- 
2.39.2