62 lines
1.8 KiB
Rust
62 lines
1.8 KiB
Rust
// Eryn Wells <eryn@erynwells.me>
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use chessfriend_board::Board;
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use chessfriend_core::{Color, Piece, Shape, score::Score};
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struct Evaluator;
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impl Evaluator {
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pub fn evaluate_symmetric_unwrapped(board: &Board, color: Color) -> Score {
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let material_balance = Self::material_balance(board, color);
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let to_move_factor = color.score_factor();
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to_move_factor * material_balance
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}
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/// Evaluate a board using the symmetric evaluation algorithm defined by
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/// Claude Shannon.
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fn material_balance(board: &Board, color: Color) -> Score {
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let other_color = color.other();
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Shape::into_iter().fold(Score::ZERO, |acc, shape| {
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let (active_pieces, other_pieces) = (
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i32::from(board.count_piece(&Piece::new(color, shape))),
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i32::from(board.count_piece(&Piece::new(other_color, shape))),
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);
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let factor = shape.score() * (active_pieces - other_pieces);
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acc + factor
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})
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use chessfriend_board::fen;
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#[test]
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fn pawn_material_balance() -> Result<(), Box<dyn std::error::Error>> {
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let board = fen!("8/8/8/8/8/3P4/8/8 w - - 0 1")?;
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assert_eq!(
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Evaluator::material_balance(&board, Color::White),
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100i32.into()
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);
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let board = fen!("8/8/3p4/8/8/3P4/8/8 w - - 0 1")?;
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assert_eq!(Evaluator::material_balance(&board, Color::White), 0.into());
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Ok(())
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}
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#[test]
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fn starting_position_is_even() {
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let board = Board::starting(None);
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assert_eq!(
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Evaluator::evaluate_symmetric_unwrapped(&board, Color::White),
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Evaluator::evaluate_symmetric_unwrapped(&board, Color::Black)
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);
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}
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}
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