From e0bd0f250b861bfd4ee2999fc518eaf9b0a58941 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Tue, 11 Sep 2012 20:00:58 +0200
Subject: [PATCH] Speed-up generate<LEGAL>

The trick here is to check for legality only in the
(rare) cases we have pinned pieces or a king move
or an en-passant.

This trick is able to increase the speed of perft
of more then 20%!

No functional change.
---
 src/movegen.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/movegen.cpp b/src/movegen.cpp
index 0b46298b..4a190345 100644
--- a/src/movegen.cpp
+++ b/src/movegen.cpp
@@ -420,11 +420,13 @@ MoveStack* generate<LEGAL>(const Position& pos, MoveStack* mlist) {
 
   MoveStack *end, *cur = mlist;
   Bitboard pinned = pos.pinned_pieces();
+  Square ksq = pos.king_square(pos.side_to_move());
 
   end = pos.in_check() ? generate<EVASIONS>(pos, mlist)
                        : generate<NON_EVASIONS>(pos, mlist);
   while (cur != end)
-      if (!pos.pl_move_is_legal(cur->move, pinned))
+      if (   (pinned || from_sq(cur->move) == ksq || type_of(cur->move) == ENPASSANT)
+          && !pos.pl_move_is_legal(cur->move, pinned))
           cur->move = (--end)->move;
       else
           cur++;
-- 
2.39.2