feat: better move ordering

use transposition table as the primary heuristic

src/lib.rs

@@ -69,7 +69,7 @@ impl From<Color> for char {
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
-enum Piece {
+pub enum Piece {
     Rook,
     Bishop,
     Knight,

src/main.rs

@@ -135,18 +135,26 @@ fn cmd_go(mut tokens: std::str::SplitWhitespace<'_>, state: &mut MainState) {
         }
     }
 
-    let (ourtime_ms, theirtime_ms) = if state.board.get_turn() == Color::White {
+    let (mut ourtime_ms, theirtime_ms) = if state.board.get_turn() == Color::White {
         (wtime, btime)
     } else {
         (btime, wtime)
     };
 
+    if ourtime_ms == 0 {
+        ourtime_ms = 300_000
+    }
+
     state
         .tx_engine
         .send(MsgToEngine::Go(Box::new(GoMessage {
             board: state.board,
             config: state.config,
-            time_lims: TimeLimits::from_ourtime_theirtime(ourtime_ms, theirtime_ms),
+            time_lims: TimeLimits::from_ourtime_theirtime(
+                ourtime_ms,
+                theirtime_ms,
+                eval_metrics(&state.board),
+            ),
         })))
         .unwrap();
 }
@@ -217,7 +225,7 @@ fn outp_bestmove(bestmove: MsgBestmove) {
     );
     match bestmove.eval {
         SearchEval::Checkmate(n) => println!("info score mate {}", n / 2),
-        SearchEval::Centipawns(eval) => {
+        SearchEval::Exact(eval) | SearchEval::Lower(eval) | SearchEval::Upper(eval) => {
             println!("info score cp {}", eval,)
         }
         SearchEval::Stopped => {

src/prelude.rs

@@ -13,9 +13,9 @@ Copyright © 2024 dogeystamp <dogeystamp@disroot.org>
 
 //! Prelude that you can import entirely to use the library conveniently.
 
-pub use crate::eval::{eval_metrics, EvalMetrics};
+pub use crate::eval::{eval_metrics, EvalMetrics, EvalInt, Eval};
 pub use crate::fen::{FromFen, ToFen};
 pub use crate::movegen::{FromUCIAlgebraic, Move, MoveGen, ToUCIAlgebraic};
 pub use crate::search::{best_line, best_move, SearchEval, TranspositionTable, EngineState, SearchConfig, TimeLimits};
-pub use crate::{Board, Color, BOARD_HEIGHT, BOARD_WIDTH, N_COLORS, N_PIECES, N_SQUARES};
+pub use crate::{Board, Color, BOARD_HEIGHT, BOARD_WIDTH, N_COLORS, N_PIECES, N_SQUARES, ColPiece, Piece};
 pub use crate::coordination::{UCIMode, UCIModeTransition, UCIModeMachine, MsgBestmove, MsgToMain, MsgToEngine, GoMessage};

src/search.rs

@@ -13,14 +13,11 @@ Copyright © 2024 dogeystamp <dogeystamp@disroot.org>
 
 //! Game-tree search.
 
-use crate::coordination::MsgToEngine;
-use crate::eval::{Eval, EvalInt};
 use crate::hash::ZobristTable;
-use crate::movegen::{Move, MoveGen};
-use crate::{Board, Piece};
+use crate::prelude::*;
 use std::cmp::{max, min};
 use std::sync::mpsc;
-use std::time::{Instant, Duration};
+use std::time::{Duration, Instant};
 
 // min can't be represented as positive
 const EVAL_WORST: EvalInt = -(EvalInt::MAX);
@@ -43,8 +40,12 @@ mod test_eval_int {
 pub enum SearchEval {
     /// Mate in |n| - 1 half moves, negative for own mate.
     Checkmate(i8),
-    /// Centipawn score.
-    Centipawns(EvalInt),
+    /// Centipawn score (exact).
+    Exact(EvalInt),
+    /// Centipawn score (lower bound).
+    Lower(EvalInt),
+    /// Centipawn score (upper bound).
+    Upper(EvalInt),
     /// Search was hard-stopped.
     Stopped,
 }
@@ -61,7 +62,9 @@ impl SearchEval {
                     Self::Checkmate(-(n + 1))
                 }
             }
-            SearchEval::Centipawns(eval) => Self::Centipawns(-eval),
+            SearchEval::Exact(eval) => Self::Exact(-eval),
+            SearchEval::Lower(eval) => Self::Upper(-eval),
+            SearchEval::Upper(eval) => Self::Lower(-eval),
             SearchEval::Stopped => SearchEval::Stopped,
         }
     }
@@ -78,7 +81,9 @@ impl From<SearchEval> for EvalInt {
                     EVAL_BEST - EvalInt::from(n)
                 }
             }
-            SearchEval::Centipawns(eval) => eval,
+            SearchEval::Exact(eval) => eval,
+            SearchEval::Lower(eval) => eval,
+            SearchEval::Upper(eval) => eval,
             SearchEval::Stopped => panic!("Attempted to evaluate a halted search"),
         }
     }
@@ -123,14 +128,6 @@ impl Default for SearchConfig {
     }
 }
 
-/// If a move is a capture, return which piece is capturing what.
-fn move_get_capture(board: &mut Board, mv: &Move) -> Option<(Piece, Piece)> {
-    // TODO: en passant
-    board
-        .get_piece(mv.dest)
-        .map(|cap_pc| (board.get_piece(mv.src).unwrap().into(), cap_pc.into()))
-}
-
 /// Least valuable victim, most valuable attacker heuristic for captures.
 fn lvv_mva_eval(src_pc: Piece, cap_pc: Piece) -> EvalInt {
     let pc_values = [500, 300, 300, 20000, 900, 100];
@@ -138,14 +135,23 @@ fn lvv_mva_eval(src_pc: Piece, cap_pc: Piece) -> EvalInt {
 }
 
 /// Assign a priority to a move based on how promising it is.
-fn move_priority(board: &mut Board, mv: &Move) -> EvalInt {
+fn move_priority(board: &mut Board, mv: &Move, state: &mut EngineState) -> EvalInt {
     // move eval
     let mut eval: EvalInt = 0;
-    if let Some((src_pc, cap_pc)) = move_get_capture(board, mv) {
+    let src_pc = board.get_piece(mv.src).unwrap();
+    let anti_mv = mv.make(board);
+
+    if state.config.enable_trans_table {
+        if let Some(entry) = &state.cache[board.zobrist] {
+            eval = entry.eval.into();
+        }
+    } else if let Some(cap_pc) = anti_mv.cap {
         // least valuable victim, most valuable attacker
-        eval += lvv_mva_eval(src_pc, cap_pc)
+        eval += lvv_mva_eval(src_pc.into(), cap_pc)
     }
 
+    anti_mv.unmake(board);
+
     eval
 }
 
@@ -200,7 +206,7 @@ fn minmax(
 
     if depth == 0 {
         let eval = board.eval() * EvalInt::from(board.turn.sign());
-        return (Vec::new(), SearchEval::Centipawns(eval));
+        return (Vec::new(), SearchEval::Exact(eval));
     }
 
     let mut mvs: Vec<_> = board
@@ -208,17 +214,17 @@ fn minmax(
         .into_iter()
         .collect::<Vec<_>>()
         .into_iter()
-        .map(|mv| (move_priority(board, &mv), mv))
+        .map(|mv| (move_priority(board, &mv, state), mv))
         .collect();
 
     // get transposition table entry
     if state.config.enable_trans_table {
         if let Some(entry) = &state.cache[board.zobrist] {
-            // the entry has a deeper knowledge than we do, so follow its best move exactly instead of
-            // just prioritizing what it thinks is best
             if entry.depth >= depth {
-                // we don't save PV line in transposition table, so no information on that
-                return (vec![entry.best_move], entry.eval);
+                if let SearchEval::Exact(_) | SearchEval::Upper(_) = entry.eval {
+                    // no point looking for a better move
+                    return (vec![entry.best_move], entry.eval);
+                }
             }
             mvs.push((EVAL_BEST, entry.best_move));
         }
@@ -227,7 +233,7 @@ fn minmax(
     // sort moves by decreasing priority
     mvs.sort_unstable_by_key(|mv| -mv.0);
 
-    let mut abs_best = SearchEval::Centipawns(EVAL_WORST);
+    let mut abs_best = SearchEval::Exact(EVAL_WORST);
     let mut best_move: Option<Move> = None;
     let mut best_continuation: Vec<Move> = Vec::new();
 
@@ -236,7 +242,7 @@ fn minmax(
             return (Vec::new(), SearchEval::Checkmate(-1));
         } else {
             // stalemate
-            return (Vec::new(), SearchEval::Centipawns(0));
+            return (Vec::new(), SearchEval::Exact(0));
         }
     }
 
@@ -264,6 +270,9 @@ fn minmax(
             // (different moves in the parent node). Alpha > beta means the eval here is _worse_
             // for the other player, so they will never make the move that leads into this branch.
             // Therefore, we stop evaluating this branch at all.
+            if let SearchEval::Upper(eval) | SearchEval::Exact(eval) = abs_best {
+                abs_best = SearchEval::Lower(eval);
+            }
             break;
         }
     }
@@ -345,12 +354,23 @@ pub struct TimeLimits {
 
 impl TimeLimits {
     /// Make time limits based on wtime, btime (but color-independent).
-    pub fn from_ourtime_theirtime(ourtime_ms: u64, _theirtime_ms: u64) -> TimeLimits {
+    ///
+    /// Also takes in eval metrics, for instance to avoid wasting too much time in the opening.
+    pub fn from_ourtime_theirtime(
+        ourtime_ms: u64,
+        _theirtime_ms: u64,
+        eval: EvalMetrics,
+    ) -> TimeLimits {
         // hard timeout (max)
         let mut hard_ms = 100_000;
         // soft timeout (max)
         let mut soft_ms = 1_200;
 
+        // if we have more than 5 minutes, and we're out of the opening, we can afford to think longer
+        if ourtime_ms > 300_000 && eval.phase <= 13 {
+            soft_ms = 4_500
+        }
+
         let factor = if ourtime_ms > 5_000 { 10 } else { 40 };
         hard_ms = min(ourtime_ms / factor, hard_ms);
         soft_ms = min(ourtime_ms / 50, soft_ms);