feat: stand-pat on quiescence search

gotta remember that not capturing is an option too

contrib/fast-chess-tag.sh

@@ -1,21 +1,30 @@
 #!/bin/sh
 # Runs a fast-chess (https://github.com/Disservin/fastchess) tournament based
-# on two branches of the chess_inator
-# (https://github.com/dogeystamp/chess_inator) engine.
+# on two tags of the chess_inator (https://github.com/dogeystamp/chess_inator)
+# engine.
 #
 # Example usage:
 #
 #	 cd chess_tournaments
-#	 fast-chess-branch.sh quiescence no-quiescence -openings file=8moves_v3.pgn format=pgn order=random -each tc=300+0.1 -rounds 12 -repeat -concurrency 8 -recover -sprt elo0=0 elo1=10 alpha=0.05 beta=0.05
+#	 fast-chess-tag.sh quiescence no-quiescence -openings file=8moves_v3.pgn format=pgn order=random -each tc=300+0.1 -rounds 12 -repeat -concurrency 8 -recover -sprt elo0=0 elo1=10 alpha=0.05 beta=0.05
 #
-# Do not use `main` as a branch, or any other branch already checked out in
-# another directory. You need to be in a chess_inator Git repository to run
-# this script. Ensure that the repository you're in is a throw-away worktree.
-# Create one using
+# You need to be in a chess_inator Git repository to run this script. Ensure
+# that the repository you're in is a throw-away worktree. Create one using:
 #
 # 	git worktree add ../chess_tournaments
 #
 # inside the original chess_inator repo.
+#
+# To create a git tag at the current commit, run
+#
+# 	git tag [tag_name]
+#
+# or to optionally annotate the tag,
+#
+# 	git tag -a [tag_name]
+#
+# which will prompt for a message.
+#
 # Also, get an opening book from Stockfish's books:
 #
 # 	curl -O https://github.com/official-stockfish/books/raw/refs/heads/master/8moves_v3.pgn.zip
@@ -28,43 +37,45 @@
 # errors. The tournament automatically ends when a statistically significant
 # result is obtained.
 #
+# LOS stands for "likelihood of superiority", LLR "log likelihood ratio".
+#
 # By default, a PGN file will be exported with the games played, and the
 # fast-chess SPRT output will be appended. This comment may interfere with
 # importing the PGN. But Lichess will ignore it, so it's probably fine.
 
 set -e
 
-BRANCH1="$1"
-BRANCH2="$2"
+TAG1="$1"
+TAG2="$2"
 
 # if this line fails it's because you don't have enough arguments
 shift 2
 
-COMM1=$(git rev-parse --short "$BRANCH1")
-COMM2=$(git rev-parse --short "$BRANCH2")
+COMM1=$(git rev-parse --short "$TAG1")
+COMM2=$(git rev-parse --short "$TAG2")
 
 mkdir -p games
 
-PGN=games/"$BRANCH1"__"$BRANCH2".pgn
+PGN=games/"$TAG1"__"$TAG2".pgn
 
 rm -f engine1 engine2
 if [ -f "$PGN" ]; then
 	rm -i "$PGN"
 fi
 
-git switch "$BRANCH1"
+git checkout "$TAG1"
 cargo build --release
 cp target/release/chess_inator engine1
 
-git switch "$BRANCH2"
+git checkout "$TAG2"
 cargo build --release
 cp target/release/chess_inator engine2
 
 OUTPUT=$(mktemp)
 
 fastchess \
-	-engine cmd=engine1 name="c_i $BRANCH1 ($COMM1)" \
-	-engine cmd=engine2 name="c_i $BRANCH2 ($COMM2)" \
+	-engine cmd=engine1 name="c_i $TAG1 ($COMM1)" \
+	-engine cmd=engine2 name="c_i $TAG2 ($COMM2)" \
 	-pgnout file="$PGN" \
 	timeleft=true \
 	$@ \

src/eval.rs

@@ -499,6 +499,7 @@ mod tests {
         // set side to move appropriately in the fen
         //
         // otherwise the exchange doesn't work
+        use Piece::*;
         let test_cases = [
             (
                 // fen
@@ -506,12 +507,18 @@ mod tests {
                 // square where exchange happens
                 "d5",
                 // expected (signed) value gain of exchange
-                Piece::Rook.value(),
+                Rook.value(),
+            ),
+            ("8/8/4b3/2kq4/2PKP3/8/8/8 w - - 0 1", "d5", Queen.value()),
+            (
+                "r3k2r/1pq2pbp/6p1/p2Qpb2/1N6/2P3P1/PB2PPBP/R3K2R w KQkq - 0 14",
+                "e5",
+                0,
             ),
             (
-                "8/8/4b3/2kq4/2PKP3/8/8/8 w - - 0 1",
-                "d5",
-                Piece::Queen.value(),
+                "r3k2r/1pq2pbp/6p1/p3p3/P5b1/2P3P1/1BN1PPBP/R2QK2R b KQkq - 0 14",
+                "e2",
+                0,
             ),
         ];
 

src/movegen.rs

@@ -1667,25 +1667,23 @@ mod tests {
 
     #[test]
     fn test_capture_movegen() {
-        let test_cases = [(
-            // fen
-            "8/3q4/5N2/8/8/8/8/3K4 w - - 0 1",
-            // expected moves generated
-            "f6d7",
-        ),
-        (
-            "8/8/8/3pP3/2K5/8/8/8 w - d6 0 1",
-            // holy hell
-            "e5d6 c4d5",
-        ),
-        (
-            "8/2q5/3K4/8/8/8/8/8 w - - 0 1",
-            "d6c7",
-        ),
-        (
-            "2Q5/3r2R1/2B1PN2/8/3K4/8/8/8 w - - 0 1",
-            "c6d7 e6d7 c8d7 f6d7 g7d7",
-        ),
+        let test_cases = [
+            (
+                // fen
+                "8/3q4/5N2/8/8/8/8/3K4 w - - 0 1",
+                // expected moves generated
+                "f6d7",
+            ),
+            (
+                "8/8/8/3pP3/2K5/8/8/8 w - d6 0 1",
+                // holy hell
+                "e5d6 c4d5",
+            ),
+            ("8/2q5/3K4/8/8/8/8/8 w - - 0 1", "d6c7"),
+            (
+                "2Q5/3r2R1/2B1PN2/8/3K4/8/8/8 w - - 0 1",
+                "c6d7 e6d7 c8d7 f6d7 g7d7",
+            ),
         ];
 
         for (fen, expected) in test_cases {

src/prelude.rs

@@ -23,5 +23,5 @@ pub use crate::search::{
     best_line, best_move, EngineState, SearchConfig, SearchEval, TimeLimits, TranspositionTable,
 };
 pub use crate::{
-    Board, ColPiece, Color, Piece, BOARD_HEIGHT, BOARD_WIDTH, N_COLORS, N_PIECES, N_SQUARES, Square,
+    Board, ColPiece, Color, Piece, Square, BOARD_HEIGHT, BOARD_WIDTH, N_COLORS, N_PIECES, N_SQUARES,
 };

src/search.rs

@@ -122,9 +122,8 @@ impl Default for SearchConfig {
     fn default() -> Self {
         SearchConfig {
             alpha_beta_on: true,
-            // try to make this even to be more conservative and avoid horizon problem
             depth: 10,
-            qdepth: 3,
+            qdepth: 4,
             enable_trans_table: true,
             transposition_size: 24,
         }
@@ -209,13 +208,20 @@ fn minmax(board: &mut Board, state: &mut EngineState, mm: MinmaxState) -> (Vec<M
         }
     }
 
+    // quiescence stand-pat score (only calculated if needed).
+    // this is where static eval goes.
+    let mut board_eval: Option<EvalInt> = None;
+
+    if mm.quiesce {
+        board_eval = Some(board.eval() * EvalInt::from(board.turn.sign()));
+    }
+
     if mm.depth == 0 {
-        if mm.quiesce || board.recap_sq.is_none() {
-            // if we're done with quiescence, static eval.
-            // if there is no capture, skip straight to static eval.
-            let eval = board.eval() * EvalInt::from(board.turn.sign());
-            return (Vec::new(), SearchEval::Exact(eval));
+        if mm.quiesce {
+            // we hit the limit on quiescence depth
+            return (Vec::new(), SearchEval::Exact(board_eval.unwrap()));
         } else {
+            // enter quiescence search
             return minmax(
                 board,
                 state,
@@ -261,11 +267,15 @@ fn minmax(board: &mut Board, state: &mut EngineState, mm: MinmaxState) -> (Vec<M
     mvs.sort_unstable_by_key(|mv| -mv.0);
 
     let mut abs_best = SearchEval::Exact(EVAL_WORST);
+
+    if mm.quiesce {
+        // stand pat
+        abs_best = SearchEval::Exact(board_eval.unwrap());
+    }
+
     let mut best_move: Option<Move> = None;
     let mut best_continuation: Vec<Move> = Vec::new();
 
-    let n_non_qmoves = mvs.len();
-
     // determine moves that are allowed in quiescence
     if mm.quiesce {
         // use static exchange evaluation to prune moves
@@ -276,7 +286,11 @@ fn minmax(board: &mut Board, state: &mut EngineState, mm: MinmaxState) -> (Vec<M
         });
     }
 
-    if n_non_qmoves == 0 {
+    if mvs.is_empty() {
+        if mm.quiesce {
+            // use stand pat
+            return (Vec::new(), SearchEval::Exact(board_eval.unwrap()));
+        }
         let is_in_check = board.is_check(board.turn);
 
         if is_in_check {
@@ -285,10 +299,6 @@ fn minmax(board: &mut Board, state: &mut EngineState, mm: MinmaxState) -> (Vec<M
             // stalemate
             return (Vec::new(), SearchEval::Exact(0));
         }
-    } else if mvs.is_empty() {
-        // pruned all the moves due to quiescence
-        let eval = board.eval() * EvalInt::from(board.turn.sign());
-        return (Vec::new(), SearchEval::Exact(eval));
     }
 
     for (_priority, mv) in mvs {