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Remove classical evaluation

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since the introduction of NNUE (first released with Stockfish 12), we
have maintained the classical evaluation as part of SF in frozen form.
The idea that this code could lead to further inputs to the NN or
search did not materialize. Now, after five releases, this PR removes
the classical evaluation from SF. Even though this evaluation is
probably the best of its class, it has become unimportant for the
engine's strength, and there is little need to maintain this
code (roughly 25% of SF) going forward, or to expend resources on
trying to improve its integration in the NNUE eval.

Indeed, it had still a very limited use in the current SF, namely
for the evaluation of positions that are nearly decided based on
material difference, where the speed of the classical evaluation
outweights its inaccuracies. This impact on strength is small,
roughly 2Elo, and probably decreasing in importance as the TC grows.

Potentially, removal of this code could lead to the development of
techniques to have faster, but less accurate NN evaluation,
for certain positions.

STC
https://tests.stockfishchess.org/tests/view/64a320173ee09aa549c52157
Elo: -2.35 ± 1.1 (95%) LOS: 0.0%
Total: 100000 W: 24916 L: 25592 D: 49492
Ptnml(0-2): 287, 12123, 25841, 11477, 272
nElo: -4.62 ± 2.2 (95%) PairsRatio: 0.95

LTC
https://tests.stockfishchess.org/tests/view/64a320293ee09aa549c5215b
 Elo: -1.74 ± 1.0 (95%) LOS: 0.0%
Total: 100000 W: 25010 L: 25512 D: 49478
Ptnml(0-2): 44, 11069, 28270, 10579, 38
nElo: -3.72 ± 2.2 (95%) PairsRatio: 0.96

VLTC SMP
https://tests.stockfishchess.org/tests/view/64a3207c3ee09aa549c52168
 Elo: -1.70 ± 0.9 (95%) LOS: 0.0%
Total: 100000 W: 25673 L: 26162 D: 48165
Ptnml(0-2): 8, 9455, 31569, 8954, 14
nElo: -3.95 ± 2.2 (95%) PairsRatio: 0.95

closes https://github.com/official-stockfish/Stockfish/pull/4674

Bench: 1444646
This commit is contained in:
Joost VandeVondele
2023-06-01 08:09:07 +02:00
parent 6a8767a0d5
commit af110e02ec
16 changed files with 37 additions and 2745 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
src/position.cpp
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@@ -751,13 +751,10 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
else
st->nonPawnMaterial[them] -= PieceValue[MG][captured];
if (Eval::useNNUE)
{
dp.dirty_num = 2; // 1 piece moved, 1 piece captured
dp.piece[1] = captured;
dp.from[1] = capsq;
dp.to[1] = SQ_NONE;
}
dp.dirty_num = 2; // 1 piece moved, 1 piece captured
dp.piece[1] = captured;
dp.from[1] = capsq;
dp.to[1] = SQ_NONE;
// Update board and piece lists
remove_piece(capsq);
@@ -765,7 +762,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
// Update material hash key and prefetch access to materialTable
k ^= Zobrist::psq[captured][capsq];
st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
prefetch(thisThread->materialTable[st->materialKey]);
// Reset rule 50 counter
st->rule50 = 0;
@@ -792,12 +788,9 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
// Move the piece. The tricky Chess960 castling is handled earlier
if (type_of(m) != CASTLING)
{
if (Eval::useNNUE)
{
dp.piece[0] = pc;
dp.from[0] = from;
dp.to[0] = to;
}
dp.piece[0] = pc;
dp.from[0] = from;
dp.to[0] = to;
move_piece(from, to);
}
@@ -823,15 +816,12 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
remove_piece(to);
put_piece(promotion, to);
if (Eval::useNNUE)
{
// Promoting pawn to SQ_NONE, promoted piece from SQ_NONE
dp.to[0] = SQ_NONE;
dp.piece[dp.dirty_num] = promotion;
dp.from[dp.dirty_num] = SQ_NONE;
dp.to[dp.dirty_num] = to;
dp.dirty_num++;
}
// Promoting pawn to SQ_NONE, promoted piece from SQ_NONE
dp.to[0] = SQ_NONE;
dp.piece[dp.dirty_num] = promotion;
dp.from[dp.dirty_num] = SQ_NONE;
dp.to[dp.dirty_num] = to;
dp.dirty_num++;
// Update hash keys
k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
@@ -961,7 +951,7 @@ void Position::do_castling(Color us, Square from, Square& to, Square& rfrom, Squ
rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
if (Do && Eval::useNNUE)
if (Do)
{
auto& dp = st->dirtyPiece;
dp.piece[0] = make_piece(us, KING);