From: Marco Costalba <mcostalba@gmail.com>
Date: Tue, 25 Dec 2012 10:22:55 +0000 (+0100)
Subject: Small tweak in is_pseudo_legal()
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=423c6d8a8a36fcc56d421caf0bbc12f53ba62c30;ds=inline

Small tweak in is_pseudo_legal()

This is difficult code becuase a bug here could lead
to very subtle crashes in case of SMP games where we
have TT move corruption due to concurrent access.

Anyhow I have fully verified te code throwing at it
random moves. It shoudl work.

No functional change.
---

diff --git a/src/position.cpp b/src/position.cpp
index 0ed2fff4..045b10ca 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -542,7 +542,6 @@ bool Position::move_is_legal(const Move m) const {
 bool Position::is_pseudo_legal(const Move m) const {
 
   Color us = sideToMove;
-  Color them = ~sideToMove;
   Square from = from_sq(m);
   Square to = to_sq(m);
   Piece pc = piece_moved(m);
@@ -587,7 +586,7 @@ bool Position::is_pseudo_legal(const Move m) const {
       case DELTA_SE:
       // Capture. The destination square must be occupied by an enemy
       // piece (en passant captures was handled earlier).
-      if (piece_on(to) == NO_PIECE || color_of(piece_on(to)) != them)
+      if (piece_on(to) == NO_PIECE || color_of(piece_on(to)) != ~us)
           return false;
 
       // From and to files must be one file apart, avoids a7h5
@@ -636,14 +635,12 @@ bool Position::is_pseudo_legal(const Move m) const {
   {
       if (type_of(pc) != KING)
       {
-          Bitboard b = checkers();
-          Square checksq = pop_lsb(&b);
-
-          if (b) // double check ? In this case a king move is required
+          // Double check? In this case a king move is required
+          if (more_than_one(checkers()))
               return false;
 
           // Our move must be a blocking evasion or a capture of the checking piece
-          if (!((between_bb(checksq, king_square(us)) | checkers()) & to))
+          if (!((between_bb(lsb(checkers()), king_square(us)) | checkers()) & to))
               return false;
       }
       // In case of king moves under check we have to remove king so to catch