Use labels to break from outer loop, group tunable constants

src/search/iterative_deepening.rs

@@ -5,7 +5,10 @@ use crate::{
     movegen::r#move::Move,
 };
 
-use super::{negamax, time::TimeInfo};
+use super::{
+    negamax, time::TimeInfo, ASPIRATION_WINDOW_DEPTH_THRESHOLD, ASPIRATION_WINDOW_EXPANSION,
+    ASPIRATION_WINDOW_INITIAL,
+};
 
 pub fn iterative_deepening(
     game: &mut Game,
@@ -15,51 +18,44 @@ pub fn iterative_deepening(
     let mut best_move = None;
     let mut best_score = MIN_SCORE;
 
-    for depth in 1..=max_depth {
+    'iterative_deepening: for depth in 1..=max_depth {
         if time.exceed_soft_limit() {
             println!("Soft limit exceeded in negamax");
             return Ok(best_move);
         }
 
         let mut nodes = 0;
-
         let mut score;
 
-        if depth < 4 {
+        if depth < ASPIRATION_WINDOW_DEPTH_THRESHOLD {
             score = negamax::negamax(game, MIN_SCORE, MAX_SCORE, depth, 0, time, &mut nodes, true);
         } else {
-            let mut window_size = 20;
+            let mut window_size = ASPIRATION_WINDOW_INITIAL;
             let mut alpha = (best_score - window_size).max(MIN_SCORE);
             let mut beta = (best_score + window_size).min(MAX_SCORE);
-            let mut break_from_aw = true;
 
-            loop {
+            'aspiration_windows: loop {
                 score = negamax::negamax(game, alpha, beta, depth, 0, time, &mut nodes, true);
 
                 let score = match score {
                     Ok(score) => score,
                     Err(ref e) => {
                         println!("Error: {}", Response::Info(e.to_string()));
-                        break_from_aw = false;
-                        break;
+                        break 'iterative_deepening;
                     }
                 };
 
                 if score >= beta {
                     beta = MAX_SCORE.min(beta.saturating_add(window_size));
-                    window_size = window_size.saturating_mul(2);
+                    window_size = window_size.saturating_mul(ASPIRATION_WINDOW_EXPANSION);
                 } else if score <= alpha {
                     alpha = MIN_SCORE.max(alpha.saturating_sub(window_size));
-                    window_size = window_size.saturating_mul(2);
+                    window_size = window_size.saturating_mul(ASPIRATION_WINDOW_EXPANSION);
                 } else {
                     best_score = score;
-                    break;
+                    break 'aspiration_windows;
                 }
             }
-
-            if !break_from_aw {
-                break;
-            }
         }
 
         if let Err(e) = score {

src/search/mod.rs

@@ -13,3 +13,14 @@ pub const HARD_LIMIT_DIVISION: u128 = 3;
 pub const SOFT_LIMIT_DIVISION: u128 = 20;
 pub const TT_SIZE_IN_MB: usize = 64;
 pub const MAX_HISTORY: i16 = 8192;
+pub const ASPIRATION_WINDOW_INITIAL: i16 = 20;
+pub const ASPIRATION_WINDOW_DEPTH_THRESHOLD: u8 = 4;
+pub const ASPIRATION_WINDOW_EXPANSION: i16 = 2;
+pub const LMR_DEPTH_THRESHOLD: u8 = 2;
+pub const LMR_MOVE_COUNT_THRESHOLD: u8 = 3;
+pub const LMR_REDUCTION: u8 = 2;
+pub const NMP_REDUCTION: u8 = 2;
+pub const NMP_DEPTH_THRESHOLD: u8 = 2;
+pub const RFP_DEPTH_LIMIT: u8 = 6;
+pub const RFP_MARGIN: u8 = 75;
+pub const CHECK_EXTENSION: u8 = 1;

src/search/negamax.rs

@@ -10,7 +10,8 @@ use super::{
     quiescence::quiescence,
     time::TimeInfo,
     transposition_table::{NodeType, TTEntry},
-    MAX_HISTORY,
+    CHECK_EXTENSION, LMR_DEPTH_THRESHOLD, LMR_MOVE_COUNT_THRESHOLD, LMR_REDUCTION, MAX_HISTORY,
+    NMP_DEPTH_THRESHOLD, NMP_REDUCTION, RFP_DEPTH_LIMIT, RFP_MARGIN,
 };
 
 pub fn negamax(
@@ -35,7 +36,7 @@ pub fn negamax(
     let in_check = game.board.king_under_check(color);
 
     if in_check {
-        depth += 1;
+        depth += CHECK_EXTENSION;
     }
 
     if depth == 0 {
@@ -55,15 +56,13 @@ pub fn negamax(
         }
     }
 
-    const RFP_DEPTH: u8 = 5;
-    const RFP_MARGIN: u8 = 75;
     let eval = entry
         .map(|entry| entry.score)
         .unwrap_or_else(|| pesto().eval(game));
 
     if !in_check
         && alpha == beta - 1
-        && depth <= RFP_DEPTH
+        && depth < RFP_DEPTH_LIMIT
         && eval > beta
         && eval - (RFP_MARGIN * depth) as i16 > beta
     {
@@ -73,7 +72,7 @@ pub fn negamax(
     if alpha == beta - 1
         && plies != 0
         && !in_check
-        && depth >= 3
+        && depth > NMP_DEPTH_THRESHOLD
         && do_nmp
         && game.board.non_pawn_materials() > 0
     {
@@ -82,7 +81,7 @@ pub fn negamax(
             game,
             -beta,
             -beta + 1,
-            depth - 3,
+            depth - 1 - NMP_REDUCTION,
             plies + 1,
             time,
             nodes,
@@ -124,10 +123,11 @@ pub fn negamax(
         let score = if legal_moves == 1 {
             -negamax(game, -beta, -alpha, depth - 1, plies + 1, time, nodes, true)?
         } else {
-            let mut lmr_reduction = 0;
-            if !in_check && !mv.is_capture() && depth > 2 && legal_moves > 3 {
-                lmr_reduction = 2;
-            }
+            #[rustfmt::skip]
+            let lmr_reduction = if !in_check
+                && !mv.is_capture()
+                && depth > LMR_DEPTH_THRESHOLD
+                && legal_moves > LMR_MOVE_COUNT_THRESHOLD { LMR_REDUCTION } else { 0 };
 
             let mut score = -negamax(
                 game,