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Compute checkers from scratch
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This micro-optimization only complicates the code and provides no benefit.
Removing it is even a speedup on my machine (i7-3770k, linux, gcc 4.9.1):

stat        test     master    diff
mean   2,403,118  2,390,904  12,214
stdev     12,043     10,620   3,677

speedup       0.51%
P(speedup>0) 100.0%

No functional change.
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@lucasart @mcostalba
lucasart authored and mcostalba committed Feb 15, 2015
1 parent 901bfb1 commit dc13004
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Showing 4 changed files with 17 additions and 41 deletions.
32 changes: 4 additions & 28 deletions src/position.cpp
View file
Expand Up @@ -687,10 +687,10 @@ bool Position::gives_check(Move m, const CheckInfo& ci) const {
void Position::do_move(Move m, StateInfo& newSt) {

CheckInfo ci(*this);
do_move(m, newSt, ci, gives_check(m, ci));
do_move(m, newSt, gives_check(m, ci));
}

void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool givesCheck) {
void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {

assert(is_ok(m));
assert(&newSt != st);
Expand Down Expand Up @@ -848,32 +848,8 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool gives
// Update the key with the final value
st->key = k;

// Update checkers bitboard: piece must be already moved due to attacks_from()
st->checkersBB = 0;

if (givesCheck)
{
if (type_of(m) != NORMAL)
st->checkersBB = attackers_to(king_square(them)) & pieces(us);
else
{
// Direct checks
if (ci.checkSq[pt] & to)
st->checkersBB |= to;

// Discovered checks
if (ci.dcCandidates && (ci.dcCandidates & from))
{
assert(pt != QUEEN);

if (pt != ROOK)
st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(us, QUEEN, ROOK);

if (pt != BISHOP)
st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);
}
}
}
// Calculate checkers bitboard (if move is check)
st->checkersBB = givesCheck ? attackers_to(king_square(them)) & pieces(us) : 0;

sideToMove = ~sideToMove;

Expand Down
2 changes: 1 addition & 1 deletion src/position.h
View file
Expand Up @@ -139,7 +139,7 @@ class Position {

// Doing and undoing moves
void do_move(Move m, StateInfo& st);
void do_move(Move m, StateInfo& st, const CheckInfo& ci, bool givesCheck);
void do_move(Move m, StateInfo& st, bool givesCheck);
void undo_move(Move m);
void do_null_move(StateInfo& st);
void undo_null_move();
Expand Down
8 changes: 4 additions & 4 deletions src/search.cpp
View file
Expand Up @@ -158,7 +158,7 @@ uint64_t Search::perft(Position& pos, Depth depth) {
cnt = 1, nodes++;
else
{
pos.do_move(m, st, ci, pos.gives_check(m, ci));
pos.do_move(m, st, pos.gives_check(m, ci));
cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
nodes += cnt;
pos.undo_move(m);
Expand Down Expand Up @@ -694,7 +694,7 @@ namespace {
if (pos.legal(move, ci.pinned))
{
ss->currentMove = move;
pos.do_move(move, st, ci, pos.gives_check(move, ci));
pos.do_move(move, st, pos.gives_check(move, ci));
value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
pos.undo_move(move);
if (value >= rbeta)
Expand Down Expand Up @@ -886,7 +886,7 @@ namespace {
quietsSearched[quietCount++] = move;

// Step 14. Make the move
pos.do_move(move, st, ci, givesCheck);
pos.do_move(move, st, givesCheck);

// Step 15. Reduced depth search (LMR). If the move fails high it will be
// re-searched at full depth.
Expand Down Expand Up @@ -1247,7 +1247,7 @@ namespace {
ss->currentMove = move;

// Make and search the move
pos.do_move(move, st, ci, givesCheck);
pos.do_move(move, st, givesCheck);
value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
: -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
pos.undo_move(move);
Expand Down
16 changes: 8 additions & 8 deletions src/syzygy/tbprobe.cpp
View file
Expand Up @@ -369,7 +369,7 @@ static int probe_ab(Position& pos, int alpha, int beta, int *success)
if (!pos.capture(capture) || type_of(capture) == ENPASSANT
|| !pos.legal(capture, ci.pinned))
continue;
pos.do_move(capture, st, ci, pos.gives_check(capture, ci));
pos.do_move(capture, st, pos.gives_check(capture, ci));
v = -probe_ab(pos, -beta, -alpha, success);
pos.undo_move(capture);
if (*success == 0) return 0;
Expand Down Expand Up @@ -432,7 +432,7 @@ int Tablebases::probe_wdl(Position& pos, int *success)
if (type_of(capture) != ENPASSANT
|| !pos.legal(capture, ci.pinned))
continue;
pos.do_move(capture, st, ci, pos.gives_check(capture, ci));
pos.do_move(capture, st, pos.gives_check(capture, ci));
int v0 = -probe_ab(pos, -2, 2, success);
pos.undo_move(capture);
if (*success == 0) return 0;
Expand Down Expand Up @@ -495,7 +495,7 @@ static int probe_dtz_no_ep(Position& pos, int *success)
if (type_of(pos.moved_piece(move)) != PAWN || pos.capture(move)
|| !pos.legal(move, ci.pinned))
continue;
pos.do_move(move, st, ci, pos.gives_check(move, ci));
pos.do_move(move, st, pos.gives_check(move, ci));
int v = -probe_ab(pos, -2, -wdl + 1, success);
pos.undo_move(move);
if (*success == 0) return 0;
Expand All @@ -517,7 +517,7 @@ static int probe_dtz_no_ep(Position& pos, int *success)
if (pos.capture(move) || type_of(pos.moved_piece(move)) == PAWN
|| !pos.legal(move, ci.pinned))
continue;
pos.do_move(move, st, ci, pos.gives_check(move, ci));
pos.do_move(move, st, pos.gives_check(move, ci));
int v = -Tablebases::probe_dtz(pos, success);
pos.undo_move(move);
if (*success == 0) return 0;
Expand All @@ -536,7 +536,7 @@ static int probe_dtz_no_ep(Position& pos, int *success)
Move move = moves->move;
if (!pos.legal(move, ci.pinned))
continue;
pos.do_move(move, st, ci, pos.gives_check(move, ci));
pos.do_move(move, st, pos.gives_check(move, ci));
if (st.rule50 == 0) {
if (wdl == -2) v = -1;
else {
Expand Down Expand Up @@ -612,7 +612,7 @@ int Tablebases::probe_dtz(Position& pos, int *success)
if (type_of(capture) != ENPASSANT
|| !pos.legal(capture, ci.pinned))
continue;
pos.do_move(capture, st, ci, pos.gives_check(capture, ci));
pos.do_move(capture, st, pos.gives_check(capture, ci));
int v0 = -probe_ab(pos, -2, 2, success);
pos.undo_move(capture);
if (*success == 0) return 0;
Expand Down Expand Up @@ -702,7 +702,7 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoveVector& rootMoves, Va
// Probe each move.
for (size_t i = 0; i < rootMoves.size(); i++) {
Move move = rootMoves[i].pv[0];
pos.do_move(move, st, ci, pos.gives_check(move, ci));
pos.do_move(move, st, pos.gives_check(move, ci));
int v = 0;
if (pos.checkers() && dtz > 0) {
ExtMove s[192];
Expand Down Expand Up @@ -812,7 +812,7 @@ bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoveVector& rootMoves
// Probe each move.
for (size_t i = 0; i < rootMoves.size(); i++) {
Move move = rootMoves[i].pv[0];
pos.do_move(move, st, ci, pos.gives_check(move, ci));
pos.do_move(move, st, pos.gives_check(move, ci));
int v = -Tablebases::probe_wdl(pos, &success);
pos.undo_move(move);
if (!success) return false;
Expand Down

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