stellar

UCI Chess engine written in C++20
git clone git://git.dimitrijedobrota.com/stellar.git
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commit05d6b505d3935ba4ee5fe030f649aa138b9b8c6b
parent7bb17c1e229bb64c927a65833273bd21fe07e2bd
authorDimitrije Dobrota <mail@dimitrijedobrota.com>
dateSat, 5 Aug 2023 13:57:42 +0200

Late Move Reduction

Diffstat:
MCMakeLists.txt|+-
Msrc/engine/engine.c|++++++++++++++++++++++++++----------

2 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt

@@ -3,7 +3,7 @@ set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

project(
Stellar
VERSION 0.0.11
VERSION 0.0.12
DESCRIPTION "Chess engine written in C"
HOMEPAGE_URL https://git.dimitrijedobrota.com/stellar.git
LANGUAGES C

diff --git a/src/engine/engine.c b/src/engine/engine.c

@@ -14,6 +14,8 @@

#include <cul/mem.h>
#define MAX_PLY 64
#define FULL_DEPTH 4
#define REDUCTION_LIMIT 3
typedef struct Stats Stats;
struct Stats {

@@ -153,7 +155,7 @@ int negamax(Stats *stats, const Board *board, int alpha, int beta, int depth) {

move_list_sort(stats, &list);
int legal_moves = 0;
int found_pv = 0;
int searched = 0;
for (int i = 0; i < move_list_size(&list); i++) {
Move move = move_list_move(&list, i);

@@ -161,19 +163,34 @@ int negamax(Stats *stats, const Board *board, int alpha, int beta, int depth) {

if (move_make(move, &copy, 0) == 0) {
continue;
}
int makeCheck = board_isCheck(&copy);
stats->ply++;
int score = alpha;
if (found_pv)
score = -negamax(stats, &copy, -alpha - 1, -alpha, depth - 1);
// no PVS or the last one failed
if (!found_pv || (score > alpha) && (score < beta))
int score;
if (!searched) {
score = -negamax(stats, &copy, -beta, -alpha, depth - 1);
} else {
// Late Move Reduction
if (searched >= FULL_DEPTH && depth >= REDUCTION_LIMIT &&
!isCheck && !makeCheck && !move_capture(move) &&
!move_promote(move)) {
score = -negamax(stats, &copy, -alpha - 1, -alpha, depth - 2);
} else
score = alpha + 1;
// found better move
if (score > alpha) {
score = -negamax(stats, &copy, -alpha - 1, -alpha, depth - 1);
// if fail research
if (score > alpha && score < beta)
score = -negamax(stats, &copy, -beta, -alpha, depth - 1);
}
}
stats->ply--;
legal_moves++;
searched++;
if (score >= beta) {
if (!move_capture(move)) {

@@ -188,7 +205,6 @@ int negamax(Stats *stats, const Board *board, int alpha, int beta, int depth) {

stats->history_moves[piece_index(move_piece(move))]
[move_target(move)] += depth;
alpha = score;
found_pv = 1;
stats->pv_table[ply][ply] = move;
for (int i = stats->ply + 1; i < stats->pv_length[ply + 1]; i++)
stats->pv_table[ply][i] = stats->pv_table[ply + 1][i];

@@ -220,7 +236,7 @@ void search_position(const Board *board, int depth) {

int score = negamax(&stats, board, -50000, 50000, crnt);
printf("info score cp %d depth %d nodes %ld pv ", score, crnt,
printf("info score cp %4d depth %2d nodes %10ld pv ", score, crnt,
stats.nodes);
for (int i = 0; i < stats.pv_length[0]; i++) {