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Refactor root history into low ply history
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This patch changes root history to low ply history - butterfly history for plies < 4.
Doubles weight of this history for root, latter plies have lesser effect.
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@Vizvezdenec @PikaCat-OuO
Vizvezdenec authored and PikaCat-OuO committed Oct 4, 2024
1 parent e176dcd commit 3bf3b93
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Showing 4 changed files with 42 additions and 49 deletions.
12 changes: 6 additions & 6 deletions src/movepick.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -82,20 +82,20 @@ MovePicker::MovePicker(const Position& p,
Move ttm,
Depth d,
const ButterflyHistory* mh,
const ButterflyHistory* rh,
const LowPlyHistory* lph,
const CapturePieceToHistory* cph,
const PieceToHistory** ch,
const PawnHistory* ph,
bool rn) :
int pl) :
pos(p),
mainHistory(mh),
rootHistory(rh),
lowPlyHistory(lph),
captureHistory(cph),
continuationHistory(ch),
pawnHistory(ph),
ttMove(ttm),
depth(d),
rootNode(rn) {
ply(pl) {

if (pos.checkers())
stage = EVASION_TT + !(ttm && pos.pseudo_legal(ttm));
Expand Down Expand Up @@ -185,8 +185,8 @@ void MovePicker::score() {
: (pt == KNIGHT || pt == CANNON) && bool(to & threatenedByDefender) ? 25000
: 0);

if (rootNode)
m.value += 4 * (*rootHistory)[pos.side_to_move()][m.from_to()];
if (ply < 4)
m.value += 8 * (*lowPlyHistory)[ply][m.from_to()] / (1 + 2 * ply);
}

else // Type == EVASIONS
Expand Down
12 changes: 8 additions & 4 deletions src/movepick.h
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Original file line number Diff line number Diff line change
Expand Up @@ -135,6 +135,10 @@ enum StatsType {
// see https://www.chessprogramming.org/Butterfly_Boards (~11 elo)
using ButterflyHistory = Stats<int16_t, 7183, COLOR_NB, 1 << 14>;

// LowPlyHistory is adressed by play and move's from and to squares, used
// to improve move ordering near the root
using LowPlyHistory = Stats<int16_t, 7183, 4, int(SQUARE_NB) * int(SQUARE_NB)>;

// CapturePieceToHistory is addressed by a move's [piece][to][captured piece type]
using CapturePieceToHistory = Stats<int16_t, 10692, PIECE_NB, SQUARE_NB, PIECE_TYPE_NB>;

Expand Down Expand Up @@ -195,11 +199,11 @@ class MovePicker {
Move,
Depth,
const ButterflyHistory*,
const ButterflyHistory*,
const LowPlyHistory*,
const CapturePieceToHistory*,
const PieceToHistory**,
const PawnHistory*,
bool);
int);
MovePicker(const Position&, Move, int, const CapturePieceToHistory*);
Move next_move(bool skipQuiets = false);

Expand All @@ -213,7 +217,7 @@ class MovePicker {

const Position& pos;
const ButterflyHistory* mainHistory;
const ButterflyHistory* rootHistory;
const LowPlyHistory* lowPlyHistory;
const CapturePieceToHistory* captureHistory;
const PieceToHistory** continuationHistory;
const PawnHistory* pawnHistory;
Expand All @@ -222,7 +226,7 @@ class MovePicker {
int stage;
int threshold;
Depth depth;
bool rootNode;
int ply;
ExtMove moves[MAX_MOVES];
};

Expand Down
62 changes: 25 additions & 37 deletions src/search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -93,21 +93,16 @@ Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply, int r60c);
void update_pv(Move* pv, Move move, const Move* childPv);
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
void update_quiet_histories(const Position& pos,
Stack* ss,
Search::Worker& workerThread,
Move move,
int bonus,
bool rootNode);
void update_all_stats(const Position& pos,
Stack* ss,
Search::Worker& workerThread,
Move bestMove,
Square prevSq,
ValueList<Move, 32>& quietsSearched,
ValueList<Move, 32>& capturesSearched,
Depth depth,
bool rootNode);
void update_quiet_histories(
const Position& pos, Stack* ss, Search::Worker& workerThread, Move move, int bonus);
void update_all_stats(const Position& pos,
Stack* ss,
Search::Worker& workerThread,
Move bestMove,
Square prevSq,
ValueList<Move, 32>& quietsSearched,
ValueList<Move, 32>& capturesSearched,
Depth depth);

} // namespace

Expand Down Expand Up @@ -251,7 +246,7 @@ void Search::Worker::iterative_deepening() {

int searchAgainCounter = 0;

rootHistory.fill(0);
lowPlyHistory.fill(0);

// Iterative deepening loop until requested to stop or the target depth is reached
while (++rootDepth < MAX_PLY && !threads.stop
Expand Down Expand Up @@ -455,7 +450,7 @@ void Search::Worker::iterative_deepening() {
// Reset histories, usually before a new game
void Search::Worker::clear() {
mainHistory.fill(0);
rootHistory.fill(0);
lowPlyHistory.fill(0);
captureHistory.fill(-771);
pawnHistory.fill(-1353);
pawnCorrectionHistory.fill(0);
Expand Down Expand Up @@ -601,7 +596,7 @@ Value Search::Worker::search(
{
// Bonus for a quiet ttMove that fails high (~2 Elo)
if (!ttCapture)
update_quiet_histories(pos, ss, *this, ttData.move, stat_bonus(depth), rootNode);
update_quiet_histories(pos, ss, *this, ttData.move, stat_bonus(depth));

// Extra penalty for early quiet moves of
// the previous ply (~1 Elo on STC, ~2 Elo on LTC)
Expand Down Expand Up @@ -836,8 +831,8 @@ Value Search::Worker::search(
(ss - 6)->continuationHistory};


MovePicker mp(pos, ttData.move, depth, &thisThread->mainHistory, &thisThread->rootHistory,
&thisThread->captureHistory, contHist, &thisThread->pawnHistory, rootNode);
MovePicker mp(pos, ttData.move, depth, &thisThread->mainHistory, &thisThread->lowPlyHistory,
&thisThread->captureHistory, contHist, &thisThread->pawnHistory, ss->ply);

value = bestValue;

Expand Down Expand Up @@ -1263,8 +1258,7 @@ Value Search::Worker::search(
// If there is a move that produces search value greater than alpha,
// we update the stats of searched moves.
else if (bestMove)
update_all_stats(pos, ss, *this, bestMove, prevSq, quietsSearched, capturesSearched, depth,
rootNode);
update_all_stats(pos, ss, *this, bestMove, prevSq, quietsSearched, capturesSearched, depth);

// Bonus for prior countermove that caused the fail low
else if (!priorCapture && prevSq != SQ_NONE)
Expand Down Expand Up @@ -1476,9 +1470,8 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta)
// Initialize a MovePicker object for the current position, and prepare to search
// the moves. We presently use two stages of move generator in quiescence search:
// captures, or evasions only when in check.
MovePicker mp(pos, ttData.move, DEPTH_QS, &thisThread->mainHistory, &thisThread->rootHistory,
&thisThread->captureHistory, contHist, &thisThread->pawnHistory,
nodeType == Root);
MovePicker mp(pos, ttData.move, DEPTH_QS, &thisThread->mainHistory, &thisThread->lowPlyHistory,
&thisThread->captureHistory, contHist, &thisThread->pawnHistory, ss->ply);

// Step 5. Loop through all pseudo-legal moves until no moves remain or a beta
// cutoff occurs.
Expand Down Expand Up @@ -1668,8 +1661,7 @@ void update_all_stats(const Position& pos,
Square prevSq,
ValueList<Move, 32>& quietsSearched,
ValueList<Move, 32>& capturesSearched,
Depth depth,
bool rootNode) {
Depth depth) {

CapturePieceToHistory& captureHistory = workerThread.captureHistory;
Piece moved_piece = pos.moved_piece(bestMove);
Expand All @@ -1680,11 +1672,11 @@ void update_all_stats(const Position& pos,

if (!pos.capture(bestMove))
{
update_quiet_histories(pos, ss, workerThread, bestMove, quietMoveBonus, rootNode);
update_quiet_histories(pos, ss, workerThread, bestMove, quietMoveBonus);

// Decrease stats for all non-best quiet moves
for (Move move : quietsSearched)
update_quiet_histories(pos, ss, workerThread, move, -quietMoveMalus, rootNode);
update_quiet_histories(pos, ss, workerThread, move, -quietMoveMalus);
}
else
{
Expand Down Expand Up @@ -1726,17 +1718,13 @@ void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {

// Updates move sorting heuristics

void update_quiet_histories(const Position& pos,
Stack* ss,
Search::Worker& workerThread,
Move move,
int bonus,
bool rootNode) {
void update_quiet_histories(
const Position& pos, Stack* ss, Search::Worker& workerThread, Move move, int bonus) {

Color us = pos.side_to_move();
workerThread.mainHistory[us][move.from_to()] << bonus;
if (rootNode)
workerThread.rootHistory[us][move.from_to()] << bonus;
if (ss->ply < 4)
workerThread.lowPlyHistory[ss->ply][move.from_to()] << bonus;

update_continuation_histories(ss, pos.moved_piece(move), move.to_sq(), bonus);

Expand Down
5 changes: 3 additions & 2 deletions src/search.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -245,8 +245,9 @@ class Worker {
void ensure_network_replicated();

// Public because they need to be updatable by the stats
ButterflyHistory mainHistory;
ButterflyHistory rootHistory;
ButterflyHistory mainHistory;
LowPlyHistory lowPlyHistory;

CapturePieceToHistory captureHistory;
ContinuationHistory continuationHistory[2][2];
PawnHistory pawnHistory;
Expand Down

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