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Futility pruning simplification

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1/ eval margin and gains removed:
16bit are now free on TT entries, due to the removal of eval margin. may be useful
in the future :) gains removed: use instead by Value(128). search() and qsearch()
are now consistent in this regard.

2/ futility_margin()
linear formula instead of complex (log(depth), movecount) formula.

3/ unify pre & post futility pruning
pre futility pruning used depth < 7 plies, while post futility pruning used
depth < 4 plies. Now it's always depth < 7.

Tested with fixed number of games both at short TC:
ELO: 0.82 +-2.1 (95%) LOS: 77.3%
Total: 40000 W: 7939 L: 7845 D: 24216

And long TC
ELO: 0.59 +-2.0 (95%) LOS: 71.9%
Total: 40000 W: 6876 L: 6808 D: 26316

bench 7243575
This commit is contained in:
Lucas Braesch 2013-11-08 18:42:22 +08:00 • committed by Marco Costalba
parent 343544f3f7
commit eed508b444
7 changed files with 59 additions and 116 deletions
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38
src/evaluate.cpp
View file

@ -229,7 +229,7 @@ namespace {
// Function prototypes
template<bool Trace>
Value do_evaluate(const Position& pos, Value& margin);
Value do_evaluate(const Position& pos);
template<Color Us>
void init_eval_info(const Position& pos, EvalInfo& ei);
@ -238,7 +238,7 @@ namespace {
Score evaluate_pieces_of_color(const Position& pos, EvalInfo& ei, Score* mobility);
template<Color Us, bool Trace>
Score evaluate_king(const Position& pos, const EvalInfo& ei, Value margins[]);
Score evaluate_king(const Position& pos, const EvalInfo& ei);
template<Color Us, bool Trace>
Score evaluate_threats(const Position& pos, const EvalInfo& ei);
@ -264,8 +264,8 @@ namespace Eval {
/// values, an endgame score and a middle game score, and interpolates
/// between them based on the remaining material.
Value evaluate(const Position& pos, Value& margin) {
return do_evaluate<false>(pos, margin);
Value evaluate(const Position& pos) {
return do_evaluate<false>(pos);
}
@ -307,19 +307,14 @@ namespace Eval {
namespace {
template<bool Trace>
Value do_evaluate(const Position& pos, Value& margin) {
Value do_evaluate(const Position& pos) {
assert(!pos.checkers());
EvalInfo ei;
Value margins[COLOR_NB];
Score score, mobility[2] = { SCORE_ZERO, SCORE_ZERO };
Thread* th = pos.this_thread();
// margins[] store the uncertainty estimation of position's evaluation
// that typically is used by the search for pruning decisions.
margins[WHITE] = margins[BLACK] = VALUE_ZERO;
// Initialize score by reading the incrementally updated scores included
// in the position object (material + piece square tables) and adding
// Tempo bonus. Score is computed from the point of view of white.
@ -332,10 +327,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
// If we have a specialized evaluation function for the current material
// configuration, call it and return.
if (ei.mi->specialized_eval_exists())
{
margin = VALUE_ZERO;
return ei.mi->evaluate(pos);
}
// Probe the pawn hash table
ei.pi = Pawns::probe(pos, th->pawnsTable);
@ -353,8 +345,8 @@ Value do_evaluate(const Position& pos, Value& margin) {
// Evaluate kings after all other pieces because we need complete attack
// information when computing the king safety evaluation.
score += evaluate_king<WHITE, Trace>(pos, ei, margins)
- evaluate_king<BLACK, Trace>(pos, ei, margins);
score += evaluate_king<WHITE, Trace>(pos, ei)
- evaluate_king<BLACK, Trace>(pos, ei);
// Evaluate tactical threats, we need full attack information including king
score += evaluate_threats<WHITE, Trace>(pos, ei)
@ -401,7 +393,6 @@ Value do_evaluate(const Position& pos, Value& margin) {
sf = ScaleFactor(50);
}
margin = margins[pos.side_to_move()];
Value v = interpolate(score, ei.mi->game_phase(), sf);
// In case of tracing add all single evaluation contributions for both white and black
@ -414,9 +405,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
Score b = ei.mi->space_weight() * evaluate_space<BLACK>(pos, ei);
Tracing::add(SPACE, apply_weight(w, Weights[Space]), apply_weight(b, Weights[Space]));
Tracing::add(TOTAL, score);
Tracing::stream << "\nUncertainty margin: White: " << to_cp(margins[WHITE])
<< ", Black: " << to_cp(margins[BLACK])
<< "\nScaling: " << std::noshowpos
Tracing::stream << "\nScaling: " << std::noshowpos
<< std::setw(6) << 100.0 * ei.mi->game_phase() / 128.0 << "% MG, "
<< std::setw(6) << 100.0 * (1.0 - ei.mi->game_phase() / 128.0) << "% * "
<< std::setw(6) << (100.0 * sf) / SCALE_FACTOR_NORMAL << "% EG.\n"
@ -640,7 +629,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
// evaluate_king() assigns bonuses and penalties to a king of a given color
template<Color Us, bool Trace>
Score evaluate_king(const Position& pos, const EvalInfo& ei, Value margins[]) {
Score evaluate_king(const Position& pos, const EvalInfo& ei) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
@ -735,12 +724,8 @@ Value do_evaluate(const Position& pos, Value& margin) {
attackUnits = std::min(99, std::max(0, attackUnits));
// Finally, extract the king danger score from the KingDanger[]
// array and subtract the score from evaluation. Set also margins[]
// value that will be used for pruning because this value can sometimes
// be very big, and so capturing a single attacking piece can therefore
// result in a score change far bigger than the value of the captured piece.
// array and subtract the score from evaluation.
score -= KingDanger[Us == Search::RootColor][attackUnits];
margins[Us] += mg_value(KingDanger[Us == Search::RootColor][attackUnits]);
}
if (Trace)
@ -1024,8 +1009,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
stream << std::showpoint << std::showpos << std::fixed << std::setprecision(2);
std::memset(scores, 0, 2 * (TOTAL + 1) * sizeof(Score));
Value margin;
do_evaluate<true>(pos, margin);
do_evaluate<true>(pos);
std::string totals = stream.str();
stream.str("");

2
src/evaluate.h
View file

@ -27,7 +27,7 @@ class Position;
namespace Eval {
extern void init();
extern Value evaluate(const Position& pos, Value& margin);
extern Value evaluate(const Position& pos);
extern std::string trace(const Position& pos);
}

17
src/movepick.h
View file

@ -30,14 +30,13 @@
/// The Stats struct stores moves statistics. According to the template parameter
/// the class can store History, Gains and Countermoves. History records how often
/// the class can store History and Countermoves. History records how often
/// different moves have been successful or unsuccessful during the current search
/// and is used for reduction and move ordering decisions. Gains records the move's
/// best evaluation gain from one ply to the next and is used for pruning decisions.
/// and is used for reduction and move ordering decisions.
/// Countermoves store the move that refute a previous one. Entries are stored
/// according only to moving piece and destination square, hence two moves with
/// different origin but same destination and piece will be considered identical.
template<bool Gain, typename T>
template<typename T>
struct Stats {
static const Value Max = Value(2000);
@ -56,10 +55,7 @@ struct Stats {
void update(Piece p, Square to, Value v) {
if (Gain)
table[p][to] = std::max(v, table[p][to] - 1);
else if (abs(table[p][to] + v) < Max)
if (abs(table[p][to] + v) < Max)
table[p][to] += v;
}
@ -67,9 +63,8 @@ private:
T table[PIECE_NB][SQUARE_NB];
};
typedef Stats< true, Value> GainsStats;
typedef Stats<false, Value> HistoryStats;
typedef Stats<false, std::pair<Move, Move> > CountermovesStats;
typedef Stats<Value> HistoryStats;
typedef Stats<std::pair<Move, Move> > CountermovesStats;
/// MovePicker class is used to pick one pseudo legal move at a time from the

104
src/search.cpp
View file

@ -63,13 +63,10 @@ namespace {
inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
// Futility lookup tables (initialized at startup) and their access functions
Value FutilityMargins[16][64]; // [depth][moveNumber]
int FutilityMoveCounts[2][32]; // [improving][depth]
inline Value futility_margin(Depth d, int mn) {
return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
: 2 * VALUE_INFINITE;
inline Value futility_margin(Depth d) {
return Value(100 * int(d));
}
// Reduction lookup tables (initialized at startup) and their access function
@ -85,7 +82,6 @@ namespace {
double BestMoveChanges;
Value DrawValue[COLOR_NB];
HistoryStats History;
GainsStats Gains;
CountermovesStats Countermoves;
template <NodeType NT>
@ -146,10 +142,6 @@ void Search::init() {
Reductions[0][0][hd][mc] += ONE_PLY / 2;
}
// Init futility margins array
for (d = 1; d < 16; ++d) for (mc = 0; mc < 64; ++mc)
FutilityMargins[d][mc] = Value(112 * int(2.9 * log(double(d))) - 8 * mc + 45);
// Init futility move count array
for (d = 0; d < 32; ++d)
{
@ -301,7 +293,6 @@ namespace {
Value bestValue, alpha, beta, delta;
std::memset(ss-2, 0, 5 * sizeof(Stack));
(ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
depth = 0;
BestMoveChanges = 0;
@ -310,7 +301,6 @@ namespace {
TT.new_search();
History.clear();
Gains.clear();
Countermoves.clear();
PVSize = Options["MultiPV"];
@ -499,7 +489,7 @@ namespace {
Move ttMove, move, excludedMove, bestMove, threatMove;
Depth ext, newDepth;
Value bestValue, value, ttValue;
Value eval, nullValue, futilityValue;
Value eval, nullValue;
bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
bool captureOrPromotion, dangerous, doFullDepthSearch;
int moveCount, quietCount;
@ -527,7 +517,6 @@ namespace {
bestValue = -VALUE_INFINITE;
ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
ss->ply = (ss-1)->ply + 1;
ss->futilityMoveCount = 0;
(ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
@ -591,16 +580,15 @@ namespace {
// Step 5. Evaluate the position statically and update parent's gain statistics
if (inCheck)
{
ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
ss->staticEval = eval = VALUE_NONE;
goto moves_loop;
}
else if (tte)
{
// Never assume anything on values stored in TT
if ( (ss->staticEval = eval = tte->eval_value()) == VALUE_NONE
||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
eval = ss->staticEval = evaluate(pos, ss->evalMargin);
if ((ss->staticEval = eval = tte->eval_value()) == VALUE_NONE)
eval = ss->staticEval = evaluate(pos);
// Can ttValue be used as a better position evaluation?
if (ttValue != VALUE_NONE)
@ -609,21 +597,8 @@ namespace {
}
else
{
eval = ss->staticEval = evaluate(pos, ss->evalMargin);
TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
ss->staticEval, ss->evalMargin);
}
// Update gain for the parent non-capture move given the static position
// evaluation before and after the move.
if ( !pos.captured_piece_type()
&& ss->staticEval != VALUE_NONE
&& (ss-1)->staticEval != VALUE_NONE
&& (move = (ss-1)->currentMove) != MOVE_NULL
&& type_of(move) == NORMAL)
{
Square to = to_sq(move);
Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
eval = ss->staticEval = evaluate(pos);
TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval);
}
// Step 6. Razoring (skipped when in check)
@ -642,17 +617,15 @@ namespace {
return v;
}
// Step 7. Static null move pruning (skipped when in check)
// We're betting that the opponent doesn't have a move that will reduce
// the score by more than futility_margin(depth) if we do a null move.
// Step 7. Futility pruning: child node (skipped when in check)
if ( !PvNode
&& !ss->skipNullMove
&& depth < 4 * ONE_PLY
&& eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
&& depth < 7 * ONE_PLY
&& eval - futility_margin(depth) >= beta
&& abs(beta) < VALUE_MATE_IN_MAX_PLY
&& abs(eval) < VALUE_KNOWN_WIN
&& pos.non_pawn_material(pos.side_to_move()))
return eval - futility_margin(depth, (ss-1)->futilityMoveCount);
return eval - futility_margin(depth);
// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
@ -855,7 +828,7 @@ moves_loop: // When in check and at SpNode search starts from here
// Update current move (this must be done after singular extension search)
newDepth = depth - ONE_PLY + ext;
// Step 13. Futility pruning (is omitted in PV nodes)
// Step 13. Pruning at shallow depth (exclude PV nodes)
if ( !PvNode
&& !captureOrPromotion
&& !inCheck
@ -874,24 +847,25 @@ moves_loop: // When in check and at SpNode search starts from here
continue;
}
// Value based pruning
// We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
// but fixing this made program slightly weaker.
Depth predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
futilityValue = ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
+ Gains[pos.moved_piece(move)][to_sq(move)];
if (futilityValue < beta)
// Futility pruning: parent node
if (predictedDepth < 7 * ONE_PLY)
{
bestValue = std::max(bestValue, futilityValue);
Value futilityValue = ss->staticEval + futility_margin(predictedDepth) + Value(128);
if (SpNode)
if (futilityValue <= alpha)
{
splitPoint->mutex.lock();
if (bestValue > splitPoint->bestValue)
splitPoint->bestValue = bestValue;
bestValue = std::max(bestValue, futilityValue);
if (SpNode)
{
splitPoint->mutex.lock();
if (bestValue > splitPoint->bestValue)
splitPoint->bestValue = bestValue;
}
continue;
}
continue;
}
// Prune moves with negative SEE at low depths
@ -904,12 +878,7 @@ moves_loop: // When in check and at SpNode search starts from here
continue;
}
// We have not pruned the move that will be searched, but remember how
// far in the move list we are to be more aggressive in the child node.
ss->futilityMoveCount = moveCount;
}
else
ss->futilityMoveCount = 0;
// Check for legality only before to do the move
if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
@ -1079,7 +1048,7 @@ moves_loop: // When in check and at SpNode search starts from here
TT.store(posKey, value_to_tt(bestValue, ss->ply),
bestValue >= beta ? BOUND_LOWER :
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
depth, bestMove, ss->staticEval, ss->evalMargin);
depth, bestMove, ss->staticEval);
// Quiet best move: update killers, history and countermoves
if ( bestValue >= beta
@ -1172,7 +1141,7 @@ moves_loop: // When in check and at SpNode search starts from here
// Evaluate the position statically
if (InCheck)
{
ss->staticEval = ss->evalMargin = VALUE_NONE;
ss->staticEval = VALUE_NONE;
bestValue = futilityBase = -VALUE_INFINITE;
}
else
@ -1180,9 +1149,8 @@ moves_loop: // When in check and at SpNode search starts from here
if (tte)
{
// Never assume anything on values stored in TT
if ( (ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE
||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
if ((ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos);
// Can ttValue be used as a better position evaluation?
if (ttValue != VALUE_NONE)
@ -1190,14 +1158,14 @@ moves_loop: // When in check and at SpNode search starts from here
bestValue = ttValue;
}
else
ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
ss->staticEval = bestValue = evaluate(pos);
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
if (!tte)
TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
DEPTH_NONE, MOVE_NONE, ss->staticEval, ss->evalMargin);
DEPTH_NONE, MOVE_NONE, ss->staticEval);
return bestValue;
}
@ -1205,7 +1173,7 @@ moves_loop: // When in check and at SpNode search starts from here
if (PvNode && bestValue > alpha)
alpha = bestValue;
futilityBase = bestValue + ss->evalMargin + Value(128);
futilityBase = bestValue + Value(128);
}
// Initialize a MovePicker object for the current position, and prepare
@ -1294,7 +1262,7 @@ moves_loop: // When in check and at SpNode search starts from here
else // Fail high
{
TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
ttDepth, move, ss->staticEval, ss->evalMargin);
ttDepth, move, ss->staticEval);
return value;
}
@ -1309,7 +1277,7 @@ moves_loop: // When in check and at SpNode search starts from here
TT.store(posKey, value_to_tt(bestValue, ss->ply),
PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
ttDepth, bestMove, ss->staticEval, ss->evalMargin);
ttDepth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
@ -1572,7 +1540,7 @@ void RootMove::insert_pv_in_tt(Position& pos) {
tte = TT.probe(pos.key());
if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE, VALUE_NONE);
TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE);
assert(MoveList<LEGAL>(pos).contains(pv[ply]));

2
src/search.h
View file

@ -45,9 +45,7 @@ struct Stack {
Move killers[2];
Depth reduction;
Value staticEval;
Value evalMargin;
int skipNullMove;
int futilityMoveCount;
};

4
src/tt.cpp
View file

@ -89,7 +89,7 @@ const TTEntry* TranspositionTable::probe(const Key key) const {
/// more valuable than a TTEntry t2 if t1 is from the current search and t2 is from
/// a previous search, or if the depth of t1 is bigger than the depth of t2.
void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m, Value statV, Value evalM) {
void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m, Value statV) {
int c1, c2, c3;
TTEntry *tte, *replace;
@ -117,5 +117,5 @@ void TranspositionTable::store(const Key key, Value v, Bound b, Depth d, Move m,
replace = tte;
}
replace->save(key32, v, b, d, m, generation, statV, evalM);
replace->save(key32, v, b, d, m, generation, statV);
}

8
src/tt.h
View file

@ -36,7 +36,7 @@
struct TTEntry {
void save(uint32_t k, Value v, Bound b, Depth d, Move m, int g, Value ev, Value em) {
void save(uint32_t k, Value v, Bound b, Depth d, Move m, int g, Value ev) {
key32 = (uint32_t)k;
move16 = (uint16_t)m;
@ -45,7 +45,6 @@ struct TTEntry {
value16 = (int16_t)v;
depth16 = (int16_t)d;
evalValue = (int16_t)ev;
evalMargin = (int16_t)em;
}
void set_generation(uint8_t g) { generation8 = g; }
@ -56,13 +55,12 @@ struct TTEntry {
Bound bound() const { return (Bound)bound8; }
int generation() const { return (int)generation8; }
Value eval_value() const { return (Value)evalValue; }
Value eval_margin() const { return (Value)evalMargin; }
private:
uint32_t key32;
uint16_t move16;
uint8_t bound8, generation8;
int16_t value16, depth16, evalValue, evalMargin;
int16_t value16, depth16, evalValue;
};
@ -85,7 +83,7 @@ public:
void refresh(const TTEntry* tte) const;
void set_size(size_t mbSize);
void clear();
void store(const Key key, Value v, Bound type, Depth d, Move m, Value statV, Value kingD);
void store(const Key key, Value v, Bound type, Depth d, Move m, Value statV);
private:
uint32_t hashMask;