improve benchmarks and marginal perf improvements

benches/future_children.rs

@@ -1,5 +1,5 @@
-use criterion::{criterion_group, criterion_main, Criterion};
-use std::hint::black_box;
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, Throughput};
+use std::time::Duration;
 
 // use crate::future_move::FutureMove;
 use othello::{board::Board, future_moves::FutureMoves, piece::Piece};
@@ -15,9 +15,16 @@ fn future_move_bench(depth: usize, expire: usize) {
 }
 
 fn criterion_benchmark(c: &mut Criterion) {
-    c.bench_function("depth 6 expire 4", |b| {
-        b.iter(|| future_move_bench(black_box(6), black_box(4)))
+    let mut group = c.benchmark_group("future_move (expire 4)");
+    group.measurement_time(Duration::from_secs(60));
+
+    for (depth, expire) in [(2, 4), (3, 4), (4, 4), (5, 4), (6, 4)].iter() {
+        group.throughput(Throughput::Elements(*depth as u64));
+        group.bench_with_input(BenchmarkId::from_parameter(depth), depth, |b, depth| {
+            b.iter(|| future_move_bench(*depth, *expire));
         });
+    }
+    group.finish();
 }
 
 criterion_group!(benches, criterion_benchmark);

src/board.rs

@@ -166,7 +166,7 @@ impl Board {
     }
 
     /// Get a reference to a backing [`BitBoard`]
-    pub fn board(&self, color: Piece) -> &BitBoard {
+    pub const fn board(&self, color: Piece) -> &BitBoard {
         match color {
             Piece::Black => &self.black_board,
             Piece::White => &self.white_board,
@@ -174,7 +174,7 @@ impl Board {
     }
 
     /// Get a mutable reference to a backing [`BitBoard`]
-    pub fn board_mut(&mut self, color: Piece) -> &mut BitBoard {
+    pub const fn board_mut(&mut self, color: Piece) -> &mut BitBoard {
         match color {
             Piece::Black => &mut self.black_board,
             Piece::White => &mut self.white_board,
@@ -225,12 +225,13 @@ impl Board {
     }
 
     pub fn place(&mut self, i: usize, j: usize, piece: Piece) -> Result<(), &'static str> {
-        if let Some(what_if_result) = self.what_if(i, j, piece) {
+        let what_if_result = self
+            .what_if(i, j, piece)
+            .ok_or("move would not propegate")?;
+
         *self = what_if_result;
         return Ok(());
     }
-        Err("move would not propegate")
-    }
 
     /// Propegate the board and captures starting from a specific position
     fn propegate_from(&mut self, i: usize, j: usize) -> usize {

src/future_moves.rs

@@ -152,23 +152,24 @@ impl FutureMoves {
         parent_idx: usize,
         lazy_children: bool,
     ) -> Option<impl Iterator<Item = usize>> {
+        let parent = &self.arena[parent_idx];
+
         // early-exit if a winner for the parent already exists
-        if self.arena[parent_idx].winner != Winner::None {
+        if parent.winner != Winner::None {
             return None;
         }
 
-        let new_color = !self.arena[parent_idx].color;
-        let parent_lazy = self.arena[parent_idx].lazy_children;
+        let new_color = !parent.color;
         let mut new: Vec<Move> =
             // use [`Board::all_positions`] here instead of [`Board::possible_moves`]
             // because we use [`Board::what_if`] later and we want to reduce calls to [`Board::propegate_from_dry`]
             Board::all_positions()
-                .flat_map(|(i, j)| self.arena[parent_idx].board.what_if(i, j, new_color).map(|x| (i, j, x)))
+                .flat_map(|(i, j)| parent.board.what_if(i, j, new_color).map(move |x| (i, j, x)))
                 .map(|(i, j, new_board)| Move {
                     i,
                     j,
                     board: new_board,
-                    winner: new_board.game_winner(!self.arena[parent_idx].color),
+                    winner: new_board.game_winner(new_color),
                     parent: Some(parent_idx),
                     children: Vec::new(),
                     value: 0,
@@ -188,7 +189,7 @@ impl FutureMoves {
         }
 
         let start_idx = self.arena.len();
-        if parent_lazy && !lazy_children {
+        if parent.lazy_children && !lazy_children {
             self.arena[parent_idx].lazy_children = false;
             // this move's children are being regenerated after lazy child expiration, don't append first node
             if new.len() > 1 {
@@ -234,15 +235,15 @@ impl FutureMoves {
 
         for (depth, nodes) in by_depth.into_iter().enumerate().rev() {
             for idx in nodes {
-                let self_value =
-                    self.arena[idx].compute_self_value(self.agent_color) / (depth + 1) as i64;
+                let node = &self.arena[idx];
+                let self_value = node.compute_self_value(self.agent_color) / (depth + 1) as i64;
 
-                let children_value = self.arena[idx]
+                let children_value = node
                     .children
                     .iter()
                     .map(|&child| self.arena[child].value)
                     .sum::<i64>()
-                    .checked_div(self.arena[idx].children.len() as i64)
+                    .checked_div(node.children.len() as i64)
                     .unwrap_or(0);
 
                 self.arena[idx].value = self_value + children_value;
@@ -309,8 +310,7 @@ impl FutureMoves {
             .find(|(_, node)| {
                 node.parent == self.current_root
                     && self.current_root.is_some()
-                    && node.i == i
-                    && node.j == j
+                    && node.coords() == (i, j)
             })
             .map(|x| x.0)
             .inspect(|&root| self.update_root_idx(root))