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Improve comments about DEPTH constants

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Also "fix" movepicker to allow depths between CHECKS and NO_CHECKS,
which makes them easier to tweak (not that they get tweaked hardly ever)
(This was more beneficial when there was a third stage to DEPTH_QS, but
it's still an improvement now)

closes https://github.com/official-stockfish/Stockfish/pull/5205

No functional change
This commit is contained in:
Dubslow
2023-04-04 22:55:52 -05:00
committed by Disservin
parent c14b69790a
commit ed79745bb9
5 changed files with 43 additions and 26 deletions
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31
src/search.cpp
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@@ -733,7 +733,7 @@ Value Search::Worker::search(
ss->staticEval = eval = to_corrected_static_eval(unadjustedStaticEval, *thisThread, pos);
// Static evaluation is saved as it was before adjustment by correction history
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, Move::none(),
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_UNSEARCHED, Move::none(),
unadjustedStaticEval, tt.generation());
}
@@ -1387,8 +1387,11 @@ moves_loop: // When in check, search starts here
}
// Quiescence search function, which is called by the main search
// function with zero depth, or recursively with further decreasing depth per call.
// Quiescence search function, which is called by the main search function with zero depth, or
// recursively with further decreasing depth per call. With depth <= 0, we "should" be using
// static eval only, but tactical moves may confuse the static eval. To fight this horizon effect,
// we implement this qsearch of tactical moves only.
// See https://www.chessprogramming.org/Horizon_Effect and https://www.chessprogramming.org/Quiescence_Search
// (~155 Elo)
template<NodeType nodeType>
Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
@@ -1446,8 +1449,10 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta,
assert(0 <= ss->ply && ss->ply < MAX_PLY);
// Decide the replacement and cutoff priority of the qsearch TT entries
ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS;
// Note that unlike regular search, which stores literal depth, in QS we only store the
// current movegen stage. If in check, we search all evasions and thus store
// DEPTH_QS_CHECKS. (Evasions may be quiet, and _CHECKS includes quiets.)
ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NORMAL;
// Step 3. Transposition table lookup
posKey = pos.key();
@@ -1499,8 +1504,8 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta,
if (std::abs(bestValue) < VALUE_TB_WIN_IN_MAX_PLY && !PvNode)
bestValue = (3 * bestValue + beta) / 4;
if (!ss->ttHit)
tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER, DEPTH_NONE,
Move::none(), unadjustedStaticEval, tt.generation());
tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER,
DEPTH_UNSEARCHED, Move::none(), unadjustedStaticEval, tt.generation());
return bestValue;
}
@@ -1514,16 +1519,16 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta,
const PieceToHistory* contHist[] = {(ss - 1)->continuationHistory,
(ss - 2)->continuationHistory};
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
// will be generated.
// Initialize a MovePicker object for the current position, and prepare to search the moves.
// We presently use two stages of qs movegen, first captures+checks, then captures only.
// (When in check, we simply search all evasions.)
// (Presently, having the checks stage is worth only 1 Elo, and may be removable in the near future,
// which would result in only a single stage of QS movegen.)
Square prevSq = ((ss - 1)->currentMove).is_ok() ? ((ss - 1)->currentMove).to_sq() : SQ_NONE;
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory,
contHist, &thisThread->pawnHistory);
// Step 5. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
// Step 5. Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs.
while ((move = mp.next_move()) != Move::none())
{
assert(move.is_ok());