Cleanup and simplify NNUE code. A lot of optimizations happend since the NNUE was introduced and since then some parts of the code were left unused. This got to the point where asserts were have to be made just to let people know that modifying something will not have any effects or may even break everything due to the assumptions being made. Removing these parts removes those inexisting "false dependencies". Additionally: * append_changed_indices now takes the king pos and stateinfo explicitly, no more misleading pos parameter * IndexList is removed in favor of a generic ValueList. Feature transformer just instantiates the type it needs. * The update cost and refresh requirement is deferred to the feature set once again, but now doesn't go through the whole FeatureSet machinery and just calls HalfKP directly. * accumulator no longer has a singular dimension. * The PS constants and the PieceSquareIndex array are made local to the HalfKP feature set because they are specific to it and DO differ for other feature sets. * A few names are changed to more descriptive Passed STC non-regression: https://tests.stockfishchess.org/tests/view/608421dd95e7f1852abd2790 LLR: 2.95 (-2.94,2.94) <-2.50,0.50> Total: 180008 W: 16186 L: 16258 D: 147564 Ptnml(0-2): 587, 12593, 63725, 12503, 596 closes https://github.com/official-stockfish/Stockfish/pull/3441 No functional change
Unify naming convention of the NNUE code matches the rest of the stockfish code base closes https://github.com/official-stockfish/Stockfish/pull/3437 No functional change
Add Stockfish namespace. fixes #3350 and is a small cleanup that might make it easier to use SF in separate projects, like a NNUE trainer or similar. closes https://github.com/official-stockfish/Stockfish/pull/3370 No functional change.
Update copyright years No functional change
More incremental accumulator updates This patch was inspired by c065abd which updates the accumulator, if possible, based on the accumulator of two plies back if the accumulator of the preceding ply is not available. With this patch we look back even further in the position history in an attempt to reduce the number of complete recomputations. When we find a usable accumulator for the position N plies back, we also update the accumulator of the position N-1 plies back because that accumulator is most likely to be helpful later when evaluating positions in sibling branches. By not updating all intermediate accumulators immediately, we avoid doing too much work that is not certain to be useful. Overall, roughly 2-3% speedup. This patch makes the code more specific to the net architecture, changing input features of the net will require additional changes to the incremental update code as discussed in the PR #3193 and #3191. Passed STC: https://tests.stockfishchess.org/tests/view/5f9056712c92c7fe3a8c60d0 LLR: 2.94 (-2.94,2.94) {-0.25,1.25} Total: 10040 W: 1116 L: 968 D: 7956 Ptnml(0-2): 42, 722, 3365, 828, 63 closes https://github.com/official-stockfish/Stockfish/pull/3193 No functional change.
Use incremental updates more often Use incremental updates for accumulators for up to 2 plies. Do not copy accumulator. About 2% speedup. Passed STC: LLR: 2.95 (-2.94,2.94) {-0.25,1.25} Total: 21752 W: 2583 L: 2403 D: 16766 Ptnml(0-2): 128, 1761, 6923, 1931, 133 https://tests.stockfishchess.org/tests/view/5f7150cf3b22d6afa5069412 closes https://github.com/official-stockfish/Stockfish/pull/3157 No functional change
Remove EvalList This patch removes the EvalList structure from the Position object and generally simplifies the interface between do_move() and the NNUE code. The NNUE evaluation function first calculates the "accumulator". The accumulator consists of two halves: one for white's perspective, one for black's perspective. If the "friendly king" has moved or the accumulator for the parent position is not available, the accumulator for this half has to be calculated from scratch. To do this, the NNUE node needs to know the positions and types of all non-king pieces and the position of the friendly king. This information can easily be obtained from the Position object. If the "friendly king" has not moved, its half of the accumulator can be calculated by incrementally updating the accumulator for the previous position. For this, the NNUE code needs to know which pieces have been added to which squares and which pieces have been removed from which squares. In principle this information can be derived from the Position object and StateInfo struct (in the same way as undo_move() does this). However, it is probably a bit faster to prepare this information in do_move(), so I have kept the DirtyPiece struct. Since the DirtyPiece struct now stores the squares rather than "PieceSquare" indices, there are now at most three "dirty pieces" (previously two). A promotion move that captures a piece removes the capturing pawn and the captured piece from the board (to SQ_NONE) and moves the promoted piece to the promotion square (from SQ_NONE). An STC test has confirmed a small speedup: https://tests.stockfishchess.org/tests/view/5f43f06b5089a564a10d850a LLR: 2.94 (-2.94,2.94) {-0.25,1.25} Total: 87704 W: 9763 L: 9500 D: 68441 Ptnml(0-2): 426, 6950, 28845, 7197, 434 closes https://github.com/official-stockfish/Stockfish/pull/3068 No functional change
Add NNUE evaluation This patch ports the efficiently updatable neural network (NNUE) evaluation to Stockfish. Both the NNUE and the classical evaluations are available, and can be used to assign a value to a position that is later used in alpha-beta (PVS) search to find the best move. The classical evaluation computes this value as a function of various chess concepts, handcrafted by experts, tested and tuned using fishtest. The NNUE evaluation computes this value with a neural network based on basic inputs. The network is optimized and trained on the evalutions of millions of positions at moderate search depth. The NNUE evaluation was first introduced in shogi, and ported to Stockfish afterward. It can be evaluated efficiently on CPUs, and exploits the fact that only parts of the neural network need to be updated after a typical chess move. [The nodchip repository](https://github.com/nodchip/Stockfish) provides additional tools to train and develop the NNUE networks. This patch is the result of contributions of various authors, from various communities, including: nodchip, ynasu87, yaneurao (initial port and NNUE authors), domschl, FireFather, rqs, xXH4CKST3RXx, tttak, zz4032, joergoster, mstembera, nguyenpham, erbsenzaehler, dorzechowski, and vondele. This new evaluation needed various changes to fishtest and the corresponding infrastructure, for which tomtor, ppigazzini, noobpwnftw, daylen, and vondele are gratefully acknowledged. The first networks have been provided by gekkehenker and sergiovieri, with the latter net (nn-97f742aaefcd.nnue) being the current default. The evaluation function can be selected at run time with the `Use NNUE` (true/false) UCI option, provided the `EvalFile` option points the the network file (depending on the GUI, with full path). The performance of the NNUE evaluation relative to the classical evaluation depends somewhat on the hardware, and is expected to improve quickly, but is currently on > 80 Elo on fishtest: 60000 @ 10+0.1 th 1 https://tests.stockfishchess.org/tests/view/5f28fe6ea5abc164f05e4c4c ELO: 92.77 +-2.1 (95%) LOS: 100.0% Total: 60000 W: 24193 L: 8543 D: 27264 Ptnml(0-2): 609, 3850, 9708, 10948, 4885 40000 @ 20+0.2 th 8 https://tests.stockfishchess.org/tests/view/5f290229a5abc164f05e4c58 ELO: 89.47 +-2.0 (95%) LOS: 100.0% Total: 40000 W: 12756 L: 2677 D: 24567 Ptnml(0-2): 74, 1583, 8550, 7776, 2017 At the same time, the impact on the classical evaluation remains minimal, causing no significant regression: sprt @ 10+0.1 th 1 https://tests.stockfishchess.org/tests/view/5f2906a2a5abc164f05e4c5b LLR: 2.94 (-2.94,2.94) {-6.00,-4.00} Total: 34936 W: 6502 L: 6825 D: 21609 Ptnml(0-2): 571, 4082, 8434, 3861, 520 sprt @ 60+0.6 th 1 https://tests.stockfishchess.org/tests/view/5f2906cfa5abc164f05e4c5d LLR: 2.93 (-2.94,2.94) {-6.00,-4.00} Total: 10088 W: 1232 L: 1265 D: 7591 Ptnml(0-2): 49, 914, 3170, 843, 68 The needed networks can be found at https://tests.stockfishchess.org/nns It is recommended to use the default one as indicated by the `EvalFile` UCI option. Guidelines for testing new nets can be found at https://github.com/glinscott/fishtest/wiki/Creating-my-first-test#nnue-net-tests Integration has been discussed in various issues: https://github.com/official-stockfish/Stockfish/issues/2823 https://github.com/official-stockfish/Stockfish/issues/2728 The integration branch will be closed after the merge: https://github.com/official-stockfish/Stockfish/pull/2825 https://github.com/official-stockfish/Stockfish/tree/nnue-player-wip closes https://github.com/official-stockfish/Stockfish/pull/2912 This will be an exciting time for computer chess, looking forward to seeing the evolution of this approach. Bench: 4746616