chessfriend/position/src/perft.rs

// Eryn Wells <eryn@erynwells.me>

use crate::{GeneratedMove, Position, ValidateMove};

pub trait Perft {
    fn perft(&mut self, depth: usize) -> u64;
}

impl Perft for Position {
    fn perft(&mut self, depth: usize) -> u64 {
        if depth == 0 {
            return 1;
        }

        let mut total_nodes_counted = 0u64;

        let legal_moves: Vec<GeneratedMove> = self.all_legal_moves(None).collect();

        for generated_ply in legal_moves {
            let ply = generated_ply.ply();

            let has_seen_position = self
                .make_move(ply, ValidateMove::No)
                .expect("unable to make generated move");

            // Do not recursive into trees where board positions repeat.
            let nodes_counted = if has_seen_position {
                1
            } else {
                self.perft(depth - 1)
            };

            total_nodes_counted += nodes_counted;

            self.unmake_last_move().expect("unable to unmake last move");
        }

        total_nodes_counted
    }
}

impl Position {
    fn perft_recursive(&mut self, depth: usize) -> u64 {
        if depth == 0 {
            return 1;
        }

        let mut total_nodes_counted: u64 = 0;

        let legal_moves: Vec<GeneratedMove> = self.all_legal_moves(None).collect();

        for generated_ply in legal_moves {
            let ply = generated_ply.ply();

            self.make_move(ply, ValidateMove::No)
                .expect("unable to make generated move");

            let nodes_counted = self.perft_recursive(depth - 1);

            total_nodes_counted += nodes_counted;

            self.unmake_last_move().expect("unable to unmake last move");
        }

        total_nodes_counted
    }
}