src/nnue/features/half_ka_v2_hm.cpp

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2026 The Stockfish developers (see AUTHORS file)

  Stockfish is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

//Definition of input features HalfKAv2_hm of NNUE evaluation function

#include "half_ka_v2_hm.h"

#include "../../bitboard.h"
#include "../../position.h"
#include "../../types.h"
#include "../nnue_common.h"

namespace Stockfish::Eval::NNUE::Features {

// Index of a feature for a given king position and another piece on some square

IndexType HalfKAv2_hm::make_index(Color perspective, Square s, Piece pc, Square ksq) {
    const IndexType flip = 56 * perspective;
    return (IndexType(s) ^ OrientTBL[ksq] ^ flip) + PieceSquareIndex[perspective][pc]
         + KingBuckets[int(ksq) ^ flip];
}

// Get a list of indices for active features

void HalfKAv2_hm::append_active_indices(Color perspective, const Position& pos, IndexList& active) {
    Square   ksq = pos.square<KING>(perspective);
    Bitboard bb  = pos.pieces();
    while (bb)
    {
        Square s = pop_lsb(bb);
        active.push_back(make_index(perspective, s, pos.piece_on(s), ksq));
    }
}

// Get a list of indices for recently changed features

void HalfKAv2_hm::append_changed_indices(
  Color perspective, Square ksq, const DiffType& diff, IndexList& removed, IndexList& added) {
    removed.push_back(make_index(perspective, diff.from, diff.pc, ksq));
    if (diff.to != SQ_NONE)
        added.push_back(make_index(perspective, diff.to, diff.pc, ksq));

    if (diff.remove_sq != SQ_NONE)
        removed.push_back(make_index(perspective, diff.remove_sq, diff.remove_pc, ksq));

    if (diff.add_sq != SQ_NONE)
        added.push_back(make_index(perspective, diff.add_sq, diff.add_pc, ksq));
}

bool HalfKAv2_hm::requires_refresh(const DiffType& diff, Color perspective) {
    return diff.pc == make_piece(perspective, KING);
}

}  // namespace Stockfish::Eval::NNUE::Features