Fix bug in FRC castling for position search

In FRC it is essential that both pieces are taken off the board before
any of them is put back, lest they obliterate each other.

diff --git a/backend.c b/backend.c
index e474fd4..38c3533 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -11515,7 +11515,7 @@ QuickCompare (Board board, int *minCounts, int *maxCounts)
 int
 QuickScan (Board board, Move *move)
 {   // reconstruct game,and compare all positions in it
-    int cnt=0, stretch=0, total = MakePieceList(board, counts);
+    int cnt=0, stretch=0, total = MakePieceList(board, counts), delayedKing = -1;
     do {
        int piece = move->piece;
        int to = move->to, from = pieceList[piece];
@@ -11533,18 +11533,22 @@ QuickScan (Board board, Move *move)
            move++;
            continue;
          } else if(piece <= Q_BCASTL) { // castling, encoded as (Q_XCASTL, king-to) + (rook, rook-to)
+           int rook;
            piece = pieceList[piece]; // first two elements of pieceList contain King numbers
            from  = pieceList[piece]; // so this must be King
            quickBoard[from] = 0;
-           quickBoard[to] = piece;
            pieceList[piece] = to;
-           move++;
-           continue;
+           from = pieceList[(++move)->piece]; // for FRC this has to be done here
+           quickBoard[from] = 0; // rook
+           quickBoard[to] = piece;
+           to = move->to; piece = move->piece;
+           goto aftercastle;
          }
        }
        if(appData.searchMode > 2) counts[pieceType[quickBoard[to]]]--; // account capture
        if((total -= (quickBoard[to] != 0)) < soughtTotal) return -1; // piece count dropped below what we search for
        quickBoard[from] = 0;
+      aftercastle:
        quickBoard[to] = piece;
        pieceList[piece] = to;
        cnt++; turn ^= 3;
@@ -11559,7 +11563,7 @@ QuickScan (Board board, Move *move)
            if(stretch++ == 0) for(i=0; i<EmptySquare; i++) lastCounts[i] = counts[i]; // remember actual material
        } else stretch = 0;
        if(stretch && (appData.searchMode == 1 || stretch >= appData.stretch)) return cnt + 1 - stretch;
-       move++;
+       move++; delayedKing = -1;
     } while(1);
 }