Skip to content

Commit

Permalink
do not reduce or extend at the root
Browse files Browse the repository at this point in the history
  • Loading branch information
@brunocodutra
brunocodutra committed Nov 20, 2024
1 parent 143d977 commit 975efe0
Showing 1 changed file with 39 additions and 72 deletions.
111 changes: 39 additions & 72 deletions lib/search/engine.rs
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use crate::nnue::{Evaluator, Value};
use crate::search::*;
use crate::util::{Assume, Counter, Integer, Timer, Trigger};
use crate::{chess::Outcome, search::*};
use arrayvec::ArrayVec;
use std::{cell::RefCell, ops::Range, time::Duration};

Expand Down Expand Up @@ -108,17 +108,6 @@ impl Engine {
Some(depth - r - (depth - ply) / 4)
}

/// A full alpha-beta search.
fn fw(
&self,
pos: &Evaluator,
depth: Depth,
ply: Ply,
ctrl: &Control,
) -> Result<Pv, Interrupted> {
self.pvs(pos, Score::lower()..Score::upper(), depth, ply, ctrl)
}

/// A [zero-window] alpha-beta search.
///
/// [zero-window]: https://www.chessprogramming.org/Null_Window
Expand Down Expand Up @@ -148,19 +137,22 @@ impl Engine {
debug_assert!(!bounds.is_empty());

ctrl.interrupted()?;
let is_root = ply == 0;
let (alpha, beta) = match pos.outcome() {
None => self.mdp(ply, &bounds),
Some(Outcome::DrawByThreefoldRepetition) if is_root => self.mdp(ply, &bounds),
Some(o) if o.is_draw() => return Ok(Pv::new(Score::new(0), None)),
Some(_) => return Ok(Pv::new(Score::lower().normalize(ply), None)),
};

let (alpha, beta) = self.mdp(ply, &bounds);
if alpha >= beta {
return Ok(Pv::new(alpha, None));
}

let transposition = match pos.outcome() {
Some(o) if o.is_draw() => return Ok(Pv::new(Score::new(0), None)),
Some(_) => return Ok(Pv::new(Score::lower().normalize(ply), None)),
None => self.tt.get(pos.zobrist()),
};

let transposition = self.tt.get(pos.zobrist());
let depth = match transposition {
_ if is_root => depth,

#[cfg(not(test))]
// Extensions are not exact.
Some(_) if pos.is_check() => depth + 1,
Expand Down Expand Up @@ -294,48 +286,46 @@ impl Engine {
) -> Pv {
let ctrl = Control::Limited(Counter::new(nodes), Timer::new(time.end), interrupter);
let mut pv = Pv::new(Score::new(0), None);
let mut depth = Depth::new(0);

while depth < Depth::upper() {
use Control::*;
pv = self.fw(pos, depth, Ply::new(0), &Unlimited).assume();
depth = depth + 1;
if pv.is_some() {
break;
}
}

'id: for d in depth.get()..=limit.get() {
'id: for depth in Depth::iter() {
let mut overtime = time.end - time.start;
let mut depth = Depth::new(d);
let mut delta: i16 = 5;
let mut draft = depth;
let mut delta = 5i16;

let (mut lower, mut upper) = match d {
let (mut lower, mut upper) = match depth.get() {
..=4 => (Score::lower(), Score::upper()),
_ => (pv.score() - delta, pv.score() + delta),
};

let ctrl = if pv.is_none() {
&Control::Unlimited
} else if depth < limit {
&ctrl
} else {
break;
};

pv = 'aw: loop {
delta = delta.saturating_mul(2);
if ctrl.timer().remaining() < Some(overtime) {
break 'id;
}

let Ok(partial) = self.pvs(pos, lower..upper, depth, Ply::new(0), &ctrl) else {
let Ok(partial) = self.pvs(pos, lower..upper, draft, Ply::new(0), ctrl) else {
break 'id;
};

match partial.score() {
score if (-lower..Score::upper()).contains(&-score) => {
overtime /= 2;
depth = Depth::new(d);
draft = depth;
upper = lower / 2 + upper / 2;
lower = score - delta;
}

score if (upper..Score::upper()).contains(&score) => {
overtime = time.end - time.start;
depth = depth - 1;
draft = draft - 1;
upper = score + delta;
pv = partial;
}
Expand Down Expand Up @@ -408,10 +398,6 @@ mod tests {
alpha
}

fn negamax(pos: &Evaluator, depth: Depth, ply: Ply) -> Score {
alphabeta(pos, Score::lower()..Score::upper(), depth, ply)
}

#[proptest]
fn hash_is_an_upper_limit_for_table_size(o: Options) {
let e = Engine::with_options(&o);
Expand Down Expand Up @@ -475,17 +461,19 @@ mod tests {
) {
e.tt.set(pos.zobrist(), Transposition::exact(d, sc, m));

let ctrl = Control::Unlimited;
assert_eq!(e.nw(&pos, b, d, p, &ctrl), Ok(Pv::new(sc, Some(m))));
assert_eq!(
e.nw(&pos, b, d, p, &Control::Unlimited),
Ok(Pv::new(sc, Some(m)))
);
}

#[proptest]
fn nw_finds_score_bound(
e: Engine,
#[by_ref] e: Engine,
pos: Evaluator,
#[filter((Value::lower()..Value::upper()).contains(&#b))] b: Score,
d: Depth,
#[filter(#p >= 0)] p: Ply,
#[filter(#p > 0)] p: Ply,
) {
assert_eq!(
e.nw(&pos, b, d, p, &Control::Unlimited)? < b,
Expand Down Expand Up @@ -564,11 +552,11 @@ mod tests {

#[proptest]
fn pvs_returns_drawn_score_if_game_ends_in_a_draw(
e: Engine,
#[by_ref] e: Engine,
#[filter(#pos.outcome().is_some_and(|o| o.is_draw()))] pos: Evaluator,
#[filter(!#b.is_empty())] b: Range<Score>,
d: Depth,
p: Ply,
#[filter(#p > 0 || #pos.outcome() != Some(Outcome::DrawByThreefoldRepetition))] p: Ply,
) {
assert_eq!(
e.pvs(&pos, b, d, p, &Control::Unlimited),
Expand All @@ -590,39 +578,18 @@ mod tests {
);
}

#[proptest]
fn fw_finds_best_score(e: Engine, pos: Evaluator, d: Depth, #[filter(#p >= 0)] p: Ply) {
assert_eq!(e.fw(&pos, d, p, &Control::Unlimited)?, negamax(&pos, d, p));
}

#[proptest]
fn fw_does_not_depend_on_configuration(
x: Options,
y: Options,
pos: Evaluator,
d: Depth,
#[filter(#p >= 0)] p: Ply,
) {
let x = Engine::with_options(&x);
let y = Engine::with_options(&y);

let ctrl = Control::Unlimited;

assert_eq!(
x.fw(&pos, d, p, &ctrl)?.score(),
y.fw(&pos, d, p, &ctrl)?.score()
);
}

#[proptest]
fn search_finds_the_principal_variation(
mut e: Engine,
pos: Evaluator,
#[filter(#d > 1)] d: Depth,
) {
let interrupter = Trigger::armed();
let time = Duration::MAX..Duration::MAX;

assert_eq!(
e.search(&pos, &Limits::Depth(d), &Trigger::armed()).score(),
e.fw(&pos, d, Ply::new(0), &Control::Unlimited)?.score()
e.search(&pos, &Limits::Depth(d), &interrupter).score(),
e.aw(&pos, d, u64::MAX, &time, &interrupter).score()
);
}

Expand Down

0 comments on commit 975efe0

Please sign in to comment.