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Retire eval margin and gains

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1/ eval margin and gains removed:
 - gains removed by Value(128): search() and qsearch() now behave consistently!

2/ futility_margin()
 - testing showed that there is no added value in this weird (log(depth), movecount)
   formula, and a much simpler linear formula is just as good. In fact, it is most
   likely better, as it is not yet optimally tuned.
 - the new simplified formula also means we get rid of FutilityMargins[], its
   initialization code, and more importantly ss->futilityMoveCount, and the hacky
   code that updates it throughout the search().
 - the current formula gives negative futility margins, and there is a hidden interaction
   between the move coutn pruning formula and the futility margin one: what happens is
   that MCP is supposed to be triggered before we use the non-sensical negative futility
   margins.

3/ unify pre & post futility pruning
 - pre futility pruning (what SF calls value based pruning) used depth < 7 plies,
   while post futility pruning (what SF calls static null move pruning) used depth < 4 plies.
 - also the condition depth < 7 in pre futility pruning was not obvious, and it seemd
   to be depth < 16 (futility_margin() returns an infinite value when 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: 10206576
This commit is contained in:
Lucas Braesch
2013-10-30 11:22:42 +08:00
committed by Marco Costalba
parent 52ae0efccf
commit ecd07e51d0
7 changed files with 47 additions and 112 deletions
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89
src/search.cpp
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@@ -63,13 +63,12 @@ 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]
Value FutilityMargins[14][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;
assert(DEPTH_ZERO <= d && d < 7 * ONE_PLY);
return FutilityMargins[d][std::min(mn, 63)];
}
// Reduction lookup tables (initialized at startup) and their access function
@@ -85,7 +84,6 @@ namespace {
double BestMoveChanges;
Value DrawValue[COLOR_NB];
HistoryStats History;
GainsStats Gains;
CountermovesStats Countermoves;
template <NodeType NT>
@@ -147,8 +145,8 @@ void Search::init() {
}
// 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);
for (d = 0; d < 14; ++d) for (mc = 0; mc < 64; ++mc)
FutilityMargins[d][mc] = Value(112 * int(2.9 * log(d >= 1 ? double(d) : 1.0)) - 8 * mc + 45);
// Init futility move count array
for (d = 0; d < 32; ++d)
@@ -301,7 +299,6 @@ 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 +307,6 @@ namespace {
TT.new_search();
History.clear();
Gains.clear();
Countermoves.clear();
PVSize = Options["MultiPV"];
@@ -499,7 +495,7 @@ 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;
@@ -591,16 +587,15 @@ 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 +604,8 @@ 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)
@@ -642,12 +624,10 @@ 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. post-Futility pruning (skipped when in check)
if ( !PvNode
&& !ss->skipNullMove
&& depth < 4 * ONE_PLY
&& depth < 7 * ONE_PLY
&& eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
&& abs(beta) < VALUE_MATE_IN_MAX_PLY
&& abs(eval) < VALUE_KNOWN_WIN
@@ -854,13 +834,13 @@ 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;
Depth predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
// Step 13. Futility pruning (is omitted in PV nodes)
if ( !PvNode
&& !captureOrPromotion
&& !inCheck
&& !dangerous
/* && move != ttMove Already implicit in the next condition */
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
// Move count based pruning
@@ -874,26 +854,6 @@ 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)
{
bestValue = std::max(bestValue, futilityValue);
if (SpNode)
{
splitPoint->mutex.lock();
if (bestValue > splitPoint->bestValue)
splitPoint->bestValue = bestValue;
}
continue;
}
// Prune moves with negative SEE at low depths
if ( predictedDepth < 4 * ONE_PLY
&& pos.see_sign(move) < 0)
@@ -1079,7 +1039,7 @@ 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 +1132,7 @@ 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 +1140,8 @@ 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 +1149,14 @@ 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 +1164,7 @@ 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 +1253,7 @@ 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 +1268,7 @@ 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 +1531,7 @@ 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]));