From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 20 Jul 2013 12:24:23 +0000 (+0200)
Subject: Fix critical SEE bug (take 2)
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=3e95800814d70587fb6b12efb33faea4c7228f88

Fix critical SEE bug (take 2)

It is somewhat unbilievable but our SEE is broken !

    If the first SEE move is a king capture and square is
    defended then SEE continues instead of breaking.

    The bug shows only on normal SEE, not see_sign() so
    probing with a:

    dbg_hit_on_c(slIndex==1, captured == KING);

    reports just a tiny:

    Total 3465656 Hits 6646 hit rate (%) 0

    Bug was there since Retire seeValues[] and move PieceValue[] out of Position of 26/6/2011 (!)
    although for some reason didn't show immediately, indeed the
    bougous patch was a "No functional change" (!!)

    bench: 4699504
---

diff --git a/src/position.cpp b/src/position.cpp
index 8ea3f00a..cecdcbf8 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1195,6 +1195,12 @@ int Position::see(Move m, int asymmThreshold) const {
   do {
       assert(slIndex < 32);
 
+      if (captured == KING) // Stop before processing a king capture
+      {
+          swapList[slIndex++] = QueenValueMg * 16;
+          break;
+      }
+
       // Add the new entry to the swap list
       swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
       slIndex++;
@@ -1205,15 +1211,6 @@ int Position::see(Move m, int asymmThreshold) const {
       stm = ~stm;
       stmAttackers = attackers & pieces(stm);
 
-      if (captured == KING)
-      {
-          // Stop before processing a king capture
-          if (stmAttackers)
-              swapList[slIndex++] = QueenValueMg * 16;
-
-          break;
-      }
-
   } while (stmAttackers);
 
   // If we are doing asymmetric SEE evaluation and the same side does the first