feat: tapered eval for endgame
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@ -99,10 +99,7 @@ fn cmd_go(mut _tokens: std::str::SplitWhitespace<'_>, board: &mut Board) {
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match eval {
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SearchEval::Checkmate(n) => println!("info score mate {}", n / 2),
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SearchEval::Centipawns(eval) => {
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println!(
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"info score cp {}",
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eval,
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)
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println!("info score cp {}", eval,)
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}
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}
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match chosen {
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157
src/eval.rs
157
src/eval.rs
@ -14,6 +14,7 @@ Copyright © 2024 dogeystamp <dogeystamp@disroot.org>
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//! Position evaluation.
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use crate::{Board, Color, Piece, Square, N_COLORS, N_PIECES, N_SQUARES};
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use core::cmp::max;
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use core::ops::Index;
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/// Signed centipawn type.
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@ -31,7 +32,7 @@ pub trait Eval {
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pub(crate) mod eval_score {
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//! Opaque "score" counters to be used in the board.
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use super::{EvalInt, Pst};
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use super::{EvalInt, PST_ENDGAME, PST_MIDGAME};
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use crate::{ColPiece, Square};
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/// Internal score-keeping for a board.
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@ -43,6 +44,43 @@ pub(crate) mod eval_score {
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pub midgame: EvalScore,
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/// End-game perspective evaluation of this board.
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pub endgame: EvalScore,
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/// Non-pawn/king piece count, used to determine when the endgame has begun.
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pub min_maj_pieces: u8,
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}
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impl EvalScores {
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/// Add/remove the value of a piece based on the PST.
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///
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/// Use +1 as sign to add, -1 to delete.
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fn change_piece(&mut self, pc: ColPiece, sq: Square, sign: i8) {
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assert!(sign == 1 || sign == -1);
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let tables = [
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(&mut self.midgame, PST_MIDGAME),
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(&mut self.endgame, PST_ENDGAME),
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];
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for (phase, pst) in tables {
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phase.score += pst[pc.pc][pc.col][sq] * EvalInt::from(pc.col.sign() * sign);
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}
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use crate::Piece::*;
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if matches!(pc.pc, Rook | Queen | Knight | Bishop) {
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match sign {
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-1 => self.min_maj_pieces -= 1,
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1 => self.min_maj_pieces += 1,
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_ => panic!(),
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}
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}
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}
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/// Remove the value of a piece on a square.
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pub fn del_piece(&mut self, pc: ColPiece, sq: Square) {
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self.change_piece(pc, sq, -1);
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}
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/// Add the value of a piece on a square.
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pub fn add_piece(&mut self, pc: ColPiece, sq: Square) {
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self.change_piece(pc, sq, 1);
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}
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}
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/// Score from a given perspective (e.g. midgame, endgame).
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@ -51,18 +89,6 @@ pub(crate) mod eval_score {
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/// Signed score.
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pub score: EvalInt,
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}
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impl EvalScore {
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/// Remove the value of a piece on a square.
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pub fn del_piece(&mut self, pc: ColPiece, sq: Square, pst: &Pst) {
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self.score -= pst[pc.pc][pc.col][sq] * EvalInt::from(pc.col.sign());
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}
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/// Add the value of a piece on a square.
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pub fn add_piece(&mut self, pc: ColPiece, sq: Square, pst: &Pst) {
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self.score += pst[pc.pc][pc.col][sq] * EvalInt::from(pc.col.sign());
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}
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}
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}
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/// The main piece-square-table (PST) type that assigns scores to pieces on given squares.
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@ -237,22 +263,97 @@ pub const PST_MIDGAME: Pst = Pst([
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], 100),
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]);
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/// Calculate evaluation without incremental updates.
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pub(crate) fn refresh_eval(board: &Board) -> EvalInt {
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let mut eval: EvalInt = 0;
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for sq in Board::squares() {
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if let Some(pc) = board.get_piece(sq) {
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eval += PST_MIDGAME[pc.pc][pc.col][sq] * EvalInt::from(pc.col.sign());
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}
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}
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eval
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}
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#[rustfmt::skip]
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pub const PST_ENDGAME: Pst = Pst([
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// rook
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make_pst([
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0, 0, 0, 0, 0, 0, 0, 0, // 8
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0, 0, 0, 0, 0, 0, 0, 0, // 7
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1, 2, 3, 1, 2, 1, 2, 1, // 6
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1, 2, 1, 2, 1, 1, 1, 1, // 5
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1, 1, 2, 1, 1, 1, 2, 1, // 4
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2, 1, 1, 0, 0, 0, 0, 0, // 3
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0, 0, 0, 0, 0, 0, 0, 0, // 2
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0, 0, 0, 0, 0, 0, 0, 0, // 1
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// a b c d e f g h
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], 500),
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// bishop
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make_pst([
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0, 0, 0, 0, 0, 0, 0, 0, // 8
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0, 0, 0, 0, 0, 0, 0, 0, // 7
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0, 0, 0, 0, 0, 0, 0, 0, // 6
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0, 0, 0, 0, 0, 0, 0, 0, // 5
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0, 0, 0, 0, 0, 0, 0, 0, // 4
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0, 0, 0, 0, 0, 0, 0, 0, // 3
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0, 0, 0, 0, 0, 0, 0, 0, // 2
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0, 0, 0, 0, 0, 0, 0, 0, // 1
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// a b c d e f g h
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], 300),
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// knight
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make_pst([
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-5, -5, -5, -5, -5, -5, -5, -5, // 8
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-5, 0, 0, 0, 0, 0, 0, -5, // 7
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-5, 0, 0, 0, 0, 0, 0, -5, // 6
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-5, 0, 0, 0, 0, 0, 0, -5, // 5
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-5, 0, 0, 0, 0, 0, 0, -5, // 4
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-5, 0, 0, 0, 0, 0, 0, -5, // 3
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-5, 0, 0, 0, 0, 0, 0, -5, // 2
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-5, -5, -5, -5, -5, -5, -5, -5, // 1
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// a b c d e f g h
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], 300),
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// king
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make_pst([
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-50, -50, -50, -50, -50, -50, -50, -50, // 8
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-50, -10, -10, -10, -10, -10, -10, -50, // 7
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-50, -10, 0, 0, 0, 0, -10, -50, // 6
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-50, -10, 0, 4, 4, 0, -10, -50, // 5
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-50, -10, 0, 4, 4, 0, -10, -50, // 4
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-50, -10, 0, 0, 0, 0, -10, -50, // 3
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-50, -10, -10, -10, -10, -10, -10, -50, // 2
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-50, -50, -50, -50, -50, -50, -50, -50, // 1
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// a b c d e f g h
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], 20_000),
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// queen
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make_pst([
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0, 0, 0, 0, 0, 0, 0, 0, // 8
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0, 0, 0, 0, 0, 0, 0, 0, // 7
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0, 0, 0, 0, 0, 0, 0, 0, // 6
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0, 0, 0, 0, 0, 0, 0, 0, // 5
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0, 0, 0, 0, 0, 0, 0, 0, // 4
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0, 0, 0, 0, 0, 0, 0, 0, // 3
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0, 0, 0, 0, 0, 0, 0, 0, // 2
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0, 0, 0, 0, 0, 0, 0, 0, // 1
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// a b c d e f g h
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], 900),
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// pawn
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make_pst([
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10, 10, 10, 10, 10, 10, 10, 10, // 8
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39, 39, 39, 39, 39, 39, 39, 39, // 7
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38, 38, 38, 38, 38, 38, 38, 38, // 6
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37, 37, 37, 38, 38, 37, 37, 37, // 5
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36, 36, 36, 36, 36, 36, 36, 36, // 4
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32, 32, 32, 34, 34, 30, 32, 30, // 3
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0, 0, 0, 0, 0, 0, 0, 0, // 2
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0, 0, 0, 0, 0, 0, 0, 0, // 1
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// a b c d e f g h
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], 100),
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]);
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impl Eval for Board {
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fn eval(&self) -> EvalInt {
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let score_incremental = self.eval.midgame.score;
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debug_assert_eq!(refresh_eval(self), score_incremental);
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self.eval.midgame.score
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// we'll define endgame as the moment when there are 7 non pawn/king pieces left on the
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// board in total.
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//
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// `phase` will range from 7 (game start) to 0 (endgame).
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let phase = i32::from(self.eval.min_maj_pieces.saturating_sub(7));
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let eval = i32::from(self.eval.midgame.score) * phase / 7
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+ i32::from(self.eval.endgame.score) * max(7 - phase, 0) / 7;
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eval.try_into().unwrap()
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}
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}
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@ -269,7 +370,7 @@ mod tests {
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let board2 = Board::from_fen("rnbqkbnr/pppppppp/8/8/8/8/8/4K3 w kq - 0 1").unwrap();
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let eval2 = board2.eval();
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assert!(eval1 > 0, "got eval {eval1}");
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assert!(eval2 < 0, "got eval {eval2}");
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assert!(eval1 > 0, "got eval {eval1} ({:?})", board1.eval);
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assert!(eval2 < 0, "got eval {eval2} ({:?})", board2.eval);
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}
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}
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@ -24,7 +24,6 @@ pub mod search;
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use crate::fen::{FromFen, ToFen, START_POSITION};
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use eval::eval_score::EvalScores;
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use eval::PST_MIDGAME;
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const BOARD_WIDTH: usize = 8;
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const BOARD_HEIGHT: usize = 8;
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@ -469,7 +468,7 @@ impl Board {
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let pl = &mut self[pc.col];
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pl[pc.into()].on_sq(sq);
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*self.mail.sq_mut(sq) = Some(pc);
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self.eval.midgame.add_piece(pc, sq, &PST_MIDGAME);
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self.eval.add_piece(pc, sq);
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dest_pc
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}
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@ -487,7 +486,7 @@ impl Board {
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let pl = &mut self[pc.col];
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pl[pc.into()].off_sq(sq);
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*self.mail.sq_mut(sq) = None;
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self.eval.midgame.del_piece(pc, sq, &PST_MIDGAME);
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self.eval.del_piece(pc, sq);
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Some(pc)
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} else {
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None
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