src/evaluate.rs

use crate::position::Position;
use crate::types::{PieceType, Color};
use crate::bitboard::{pop_lsb, EMPTY};

const MG_WEIGHTS: [i32; 7] = [0, 82, 337, 365, 477, 1025, 20000];

const PAWN_PST: [i32; 64] = [
     0,  0,  0,  0,  0,  0,  0,  0,
    50, 50, 50, 50, 50, 50, 50, 50,
    10, 10, 20, 30, 30, 20, 10, 10,
     5,  5, 10, 25, 25, 10,  5,  5,
     0,  0,  0, 20, 20,  0,  0,  0,
     5, -5,-10,  0,  0,-10, -5,  5,
     5, 10, 10,-20,-20, 10, 10,  5,
     0,  0,  0,  0,  0,  0,  0,  0
];

const KNIGHT_PST: [i32; 64] = [
    -50,-40,-30,-30,-30,-30,-40,-50,
    -40,-20,  0,  0,  0,  0,-20,-40,
    -30,  0, 10, 15, 15, 10,  0,-30,
    -30,  5, 15, 20, 20, 15,  5,-30,
    -30,  0, 15, 20, 20, 15,  0,-30,
    -30,  5, 10, 15, 15, 10,  5,-30,
    -40,-20,  0,  5,  5,  0,-20,-40,
    -50,-40,-30,-30,-30,-30,-40,-50
];

const BISHOP_PST: [i32; 64] = [
    -20,-10,-10,-10,-10,-10,-10,-20,
    -10,  0,  0,  0,  0,  0,  0,-10,
    -10,  0,  5, 10, 10,  5,  0,-10,
    -10,  5,  5, 10, 10,  5,  5,-10,
    -10,  0, 10, 10, 10, 10,  0,-10,
    -10, 10, 10, 10, 10, 10, 10,-10,
    -10,  5,  0,  0,  0,  0,  5,-10,
    -20,-10,-10,-10,-10,-10,-10,-20
];

const ROOK_PST: [i32; 64] = [
      0,  0,  0,  0,  0,  0,  0,  0,
      5, 10, 10, 10, 10, 10, 10,  5,
     -5,  0,  0,  0,  0,  0,  0, -5,
     -5,  0,  0,  0,  0,  0,  0, -5,
     -5,  0,  0,  0,  0,  0,  0, -5,
     -5,  0,  0,  0,  0,  0,  0, -5,
     -5,  0,  0,  0,  0,  0,  0, -5,
      0,  0,  0,  5,  5,  0,  0,  0
];

const QUEEN_PST: [i32; 64] = [
    -20,-10,-10, -5, -5,-10,-10,-20,
    -10,  0,  0,  0,  0,  0,  0,-10,
    -10,  0,  5,  5,  5,  5,  0,-10,
     -5,  0,  5,  5,  5,  5,  0, -5,
      0,  0,  5,  5,  5,  5,  0, -5,
    -10,  5,  5,  5,  5,  5,  0,-10,
    -10,  0,  5,  0,  0,  0,  0,-10,
    -20,-10,-10, -5, -5,-10,-10,-20
];

const KING_MG_PST: [i32; 64] = [
    -30,-40,-40,-50,-50,-40,-40,-30,
    -30,-40,-40,-50,-50,-40,-40,-30,
    -30,-40,-40,-50,-50,-40,-40,-30,
    -30,-40,-40,-50,-50,-40,-40,-30,
    -20,-30,-30,-40,-40,-30,-30,-20,
    -10,-20,-20,-20,-20,-20,-20,-10,
     20, 20,  0,  0,  0,  0, 20, 20,
     20, 30, 10,  0,  0, 10, 30, 20
];

fn mirror_sq(sq: usize) -> usize {
    sq ^ 56
}

fn get_pst_score(p_type: PieceType, sq: usize, is_white: bool) -> i32 {
    let index = if is_white { mirror_sq(sq) } else { sq };
    match p_type {
        PieceType::Pawn => PAWN_PST[index],
        PieceType::Knight => KNIGHT_PST[index],
        PieceType::Bishop => BISHOP_PST[index],
        PieceType::Rook => ROOK_PST[index],
        PieceType::Queen => QUEEN_PST[index],
        PieceType::King => KING_MG_PST[index],
        _ => 0,
    }
}

pub fn evaluate(pos: &Position) -> i32 {
    let mut score = 0;
    
    for p in 1..=6 {
        let p_type: PieceType = unsafe { std::mem::transmute(p as u8) };
        
        let mut w_pieces = pos.pieces[p] & pos.colors[Color::White as usize];
        while w_pieces != EMPTY {
            let sq = pop_lsb(&mut w_pieces) as usize;
            score += MG_WEIGHTS[p];
            score += get_pst_score(p_type, sq, true);
        }
        
        let mut b_pieces = pos.pieces[p] & pos.colors[Color::Black as usize];
        while b_pieces != EMPTY {
            let sq = pop_lsb(&mut b_pieces) as usize;
            score -= MG_WEIGHTS[p];
            score -= get_pst_score(p_type, sq, false);
        }
    }

    if pos.side_to_move == Color::White { score } else { -score }
}