From 48b74142efa52f0da9d4e27f9bbcbe9520499524 Mon Sep 17 00:00:00 2001
From: Marco Costalba <mcostalba@gmail.com>
Date: Wed, 23 Sep 2009 21:45:32 +0100
Subject: [PATCH] Micro optimization of generate_piece_moves()

This patch make the piece list always terminated by SQ_NONE,
so that we can use a simpler and faster loop in move
generation.

Speedup is about 0.6%.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---
 src/movegen.cpp  | 8 ++++----
 src/position.cpp | 3 +++
 src/position.h   | 5 +++++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/movegen.cpp b/src/movegen.cpp
index edb36fea..f83dded7 100644
--- a/src/movegen.cpp
+++ b/src/movegen.cpp
@@ -476,10 +476,10 @@ namespace {
 
     Square from;
     Bitboard b;
+    const Square* ptr = pos.piece_list_begin(us, Piece);
 
-    for (int i = 0, e = pos.piece_count(us, Piece); i < e; i++)
+    while ((from = *ptr++) != SQ_NONE)
     {
-        from = pos.piece_list(us, Piece, i);
         b = pos.attacks_from<Piece>(from) & target;
         SERIALIZE_MOVES(b);
     }
@@ -502,10 +502,10 @@ namespace {
                                      Color us, Bitboard target, Bitboard pinned) {
     Square from;
     Bitboard b;
+    const Square* ptr = pos.piece_list_begin(us, Piece);
 
-    for (int i = 0, e = pos.piece_count(us, Piece); i < e; i++)
+    while ((from = *ptr++) != SQ_NONE)
     {
-        from = pos.piece_list(us, Piece, i);
         if (pinned && bit_is_set(pinned, from))
             continue;
 
diff --git a/src/position.cpp b/src/position.cpp
index e759b642..443ba881 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -838,6 +838,7 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
       Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
       index[lastPawnSquare] = index[to];
       pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
+      pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
       index[to] = pieceCount[us][promotion] - 1;
       pieceList[us][promotion][index[to]] = to;
 
@@ -943,6 +944,7 @@ void Position::do_capture_move(Bitboard& key, PieceType capture, Color them, Squ
     Square lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
     index[lastPieceSquare] = index[capsq];
     pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
+    pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
 
     // Reset rule 50 counter
     st->rule50 = 0;
@@ -1099,6 +1101,7 @@ void Position::undo_move(Move m) {
       Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
       index[lastPromotionSquare] = index[to];
       pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
+      pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
       index[to] = pieceCount[us][PAWN] - 1;
       pieceList[us][PAWN][index[to]] = to;
   }
diff --git a/src/position.h b/src/position.h
index 88ee8fe2..370bb1d4 100644
--- a/src/position.h
+++ b/src/position.h
@@ -193,6 +193,7 @@ public:
 
   // Piece lists
   Square piece_list(Color c, PieceType pt, int index) const;
+  const Square* piece_list_begin(Color c, PieceType pt) const;
 
   // Information about attacks to or from a given square
   Bitboard attackers_to(Square s) const;
@@ -403,6 +404,10 @@ inline Square Position::piece_list(Color c, PieceType pt, int index) const {
   return pieceList[c][pt][index];
 }
 
+inline const Square* Position::piece_list_begin(Color c, PieceType pt) const {
+  return pieceList[c][pt];
+}
+
 inline Square Position::ep_square() const {
   return st->epSquare;
 }
-- 
2.39.2