bench: add board place benchmark

Cargo.toml

@@ -42,6 +42,10 @@ criterion = { version = "0.5", features = [ "html_reports" ] }
 name = "future_children"
 harness = false
 
+[[bench]]
+name = "board"
+harness = false
+
 [lints.rust]
 # fix weird warnings about `test` not being expected
 unexpected_cfgs = { level = "allow", check-cfg = ['cfg(test)'] }

benches/board.rs

@@ -0,0 +1,29 @@
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
+use othello::repr::{Board, Piece};
+
+fn fill_board(loops: usize) {
+    let mut board = Board::new();
+    board.place_unchecked((0, 1).into(), Piece::White);
+    board.place_unchecked((0, 2).into(), Piece::Black);
+    board.place_unchecked((0, 3).into(), Piece::Black);
+    board.place_unchecked((0, 4).into(), Piece::Black);
+    for _ in 0..loops {
+        let mut board = board;
+        let _ = board.place((0, 5).into(), Piece::White);
+    }
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let mut group = c.benchmark_group("board");
+
+    const LOOPS: usize = 1000;
+
+    group.throughput(Throughput::Elements(LOOPS as u64));
+    group.bench_function("board_place", |b| {
+        b.iter(|| fill_board(LOOPS));
+    });
+    group.finish();
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

benches/future_children.rs

@@ -22,7 +22,7 @@ fn criterion_benchmark(c: &mut Criterion) {
     let mut group = c.benchmark_group("extend_layer (no pruning)");
     const ARENA_SIZE: usize = 10_000_000;
 
-    for depth in 1..8 {
+    for depth in 6..8 {
         group.throughput(Throughput::Elements(
             extend_layers_no_pruning(depth, ARENA_SIZE) as u64,
         ));

src/repr/board.rs

@@ -162,8 +162,9 @@ impl Board {
     }
 
     /// Place a piece without checking for propegation of validity
+    /// only pub for setting up benchmark
     #[const_fn(cfg(not(feature = "bitvec")))]
-    const fn place_unchecked(&mut self, coord: CoordPair, piece: Piece) {
+    pub const fn place_unchecked(&mut self, coord: CoordPair, piece: Piece) {
         self.board_mut(piece).set(coord, true);
         self.board_mut(piece.flip()).set(coord, false);
     }

src/repr/chains.rs

@@ -84,7 +84,7 @@ pub fn gen_adj_lookup() -> PosMap<ChainCollection> {
                                 .map(Iterator::collect),
                         )
                         .chain(diag_raw(i_chain, j_chain).map(Iterator::collect))
-                        .filter(|x: &Vec<(u8, u8)>| !x.is_empty()) // PERF! filter out empty chains +~10-12% perf boost
+                        .filter(|x: &Vec<(u8, u8)>| !x.is_empty()) // PERF! filter out empty chains +~5% perf boost (in [`Board::place`])
                         .map(|x: Vec<(u8, u8)>| x.into_iter().map(|x| x.into()).collect()),
                 );