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Late move reduction #44

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3 changes: 3 additions & 0 deletions engine/src/opts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,9 @@ pub struct Opts {
/// Internal iterative deepening lower depth limit.
#[uci(kind = "spin", min = "5", max = "10", default = "5")]
pub iid_depth_lower_bound: Depth,
/// Late move reduction move number threshold.
#[uci(kind = "spin", min = "1", max = "256", default = "3")]
pub lmr_move_threshold: usize,

// Move ordering options:
//
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9 changes: 8 additions & 1 deletion engine/src/search/negamax.rs
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Expand Up @@ -7,6 +7,7 @@ use crate::{
evaluate::Evaluate,
movelist::MoveVec,
newtypes::{Depth, Ply, Value},
opts::OPTS,
tt::{Bound, EntryWriterOpts},
};

Expand Down Expand Up @@ -78,7 +79,13 @@ impl Searcher<'_> {
for (mv_nr, mv) in moves.iter().map(|entry| entry.mv).enumerate() {
self.make_move(board, mv, &mut new_board, ply);

let value = self.pv_search::<PV>(&new_board, depth, alpha, beta, ply, mv_nr);
let mut new_depth = depth;

if mv_nr > OPTS.lmr_move_threshold && !new_board.in_check() {
new_depth = new_depth.decrement();
}

let value = self.pv_search::<PV>(&new_board, new_depth, alpha, beta, ply, mv_nr);

if self.should_stop() {
// If we're stopping, we don't trust the value, because it was likely cut off.
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