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Fix bug in positive tt cutoff and rewrite to use mate/d in max ply #166

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Merged
dallinson merged 1 commit into from
Apr 6, 2026
Merged

Fix bug in positive tt cutoff and rewrite to use mate/d in max ply #166

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4 changes: 2 additions & 2 deletions src/evaluation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,6 @@ Score Evaluation::evaluate_board(const Position& board) {
const auto mg_phase = std::min(board.get_mg_phase(), (uint8_t) 24);
const auto eg_phase = 24 - mg_phase;

return std::clamp((((mg_score * mg_phase) + (eg_score * eg_phase)) / 24) + 5, MagicNumbers::NegativeInfinity + MAX_PLY + 1,
MagicNumbers::PositiveInfinity - MAX_PLY - 1);
return std::clamp((((mg_score * mg_phase) + (eg_score * eg_phase)) / 24) + 5, MATED_IN_MAX_PLY + 1,
MATE_IN_MAX_PLY - 1);
}
2 changes: 1 addition & 1 deletion src/history.cpp
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Expand Up @@ -87,7 +87,7 @@ Score HistoryTable::corrhist_score(const Position& pos, const Score static_eval,

const i32 adjusted_score = static_eval + (entry * std::abs(entry)) / 16384;

return std::clamp(adjusted_score, -MATE_FOUND + 1, MATE_FOUND - 1);
return std::clamp(adjusted_score, MATED_IN_MAX_PLY + 1, MATE_IN_MAX_PLY - 1);
}

void HistoryTable::update_corrhist_score(const Position& pos, const Score static_eval, const Score search_score, const int depth, const BoardHistory& hist) {
Expand Down
3 changes: 2 additions & 1 deletion src/magic_numbers.hpp
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Expand Up @@ -38,4 +38,5 @@ namespace MagicNumbers {
// int32_t so a known constant size
} // namespace MagicNumbers

constexpr static int MATE_FOUND = MagicNumbers::PositiveInfinity - MAX_PLY;
constexpr static int MATE_IN_MAX_PLY = MagicNumbers::PositiveInfinity - MAX_PLY;
constexpr static int MATED_IN_MAX_PLY = MagicNumbers::NegativeInfinity + MAX_PLY;
26 changes: 13 additions & 13 deletions src/search.cpp
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Expand Up @@ -251,9 +251,9 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
// Negative infinity is being mated at this square
// A mate score is therefore greater than (positive_infinity - max_ply) or
// less than (negative_infinity + max_ply)
if (entry->get().score() == MagicNumbers::PositiveInfinity) {
if (entry->get().score() >= MATE_IN_MAX_PLY) {
return MagicNumbers::PositiveInfinity - ply;
} else if (entry->get().score() <= (MagicNumbers::NegativeInfinity + MAX_PLY)) {
} else if (entry->get().score() <= MATED_IN_MAX_PLY) {
return MagicNumbers::NegativeInfinity + ply;
}
return entry->get().score();
Expand All @@ -274,7 +274,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
const auto raw_eval = [&]() {
if (old_pos.in_check()) {
return MagicNumbers::NegativeInfinity;
} else if (tt_hit && entry->get().static_eval() > (MagicNumbers::NegativeInfinity + MAX_PLY)) {
} else if (tt_hit && entry->get().static_eval() > MATED_IN_MAX_PLY) {
return entry->get().static_eval();
} else {
return Evaluation::evaluate_board(old_pos);
Expand All @@ -290,7 +290,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
}();

const auto static_eval = [&]() {
if (tt_hit && entry->get().score() > (MagicNumbers::NegativeInfinity + MAX_PLY)
if (tt_hit && entry->get().score() > MATED_IN_MAX_PLY
&& (entry->get().bound_type() == BoundTypes::EXACT_BOUND
|| (entry->get().bound_type() == BoundTypes::LOWER_BOUND && entry->get().score() > raw_eval)
|| (entry->get().bound_type() == BoundTypes::UPPER_BOUND && entry->get().score() < raw_eval))) {
Expand Down Expand Up @@ -342,7 +342,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be

board_hist.pop_board();
if (null_score >= beta) {
if (null_score > MagicNumbers::PositiveInfinity - MAX_PLY) {
if (null_score > MATE_IN_MAX_PLY) {
return beta;
} else {
return null_score;
Expand Down Expand Up @@ -392,7 +392,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
}

// futility pruning
if (!old_pos.in_check() && best_score > (MagicNumbers::NegativeInfinity + MAX_PLY) && !move.move.is_noisy() && depth <= fp_depth
if (!old_pos.in_check() && best_score > MATED_IN_MAX_PLY && !move.move.is_noisy() && depth <= fp_depth
&& static_eval + fp_multi * depth < alpha) {
skip_quiets = true;
continue;
Expand All @@ -408,7 +408,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
}
}

if (depth <= see_prune_depth && best_score > (MagicNumbers::NegativeInfinity + MAX_PLY)
if (depth <= see_prune_depth && best_score > MATED_IN_MAX_PLY
&& !Search::static_exchange_evaluation(
old_pos, move.move, move.move.is_noisy() ? (noisy_see_prune_multi * depth * depth) : (quiet_see_prune_multi * depth))) {
continue;
Expand All @@ -423,7 +423,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
if constexpr (node_type == NodeTypes::ROOT_NODE) return false;
if (tt_hit && depth >= 8 && move.move == entry->get().move() && !in_singular_search
&& entry->get().depth() + 4 >= depth && entry->get().bound_type() != BoundTypes::UPPER_BOUND
&& std::abs(entry->get().score()) < (MagicNumbers::PositiveInfinity - MAX_PLY)) {
&& std::abs(entry->get().score()) < MATE_IN_MAX_PLY) {
// Do SE
const auto se_depth = (depth - 1) / 2;
const auto se_beta = entry->get().score() - (3 * depth);
Expand Down Expand Up @@ -526,7 +526,7 @@ Score SearchHandler::negamax_step(const Position& old_pos, Score alpha, Score be
const BoundTypes bound_type =
(best_score >= beta ? BoundTypes::LOWER_BOUND : (alpha != original_alpha ? BoundTypes::EXACT_BOUND : BoundTypes::UPPER_BOUND));

if (!old_pos.in_check() && std::abs(best_score) < MATE_FOUND && (best_move.is_null_move() || best_move.is_quiet())
if (!old_pos.in_check() && std::abs(best_score) < MATE_IN_MAX_PLY && (best_move.is_null_move() || best_move.is_quiet())
&& !(bound_type == BoundTypes::LOWER_BOUND && best_score <= adjusted_eval)
&& !(bound_type == BoundTypes::UPPER_BOUND && best_score >= adjusted_eval)) {
history_table.update_corrhist_score(old_pos, adjusted_eval, best_score, depth, board_hist);
Expand Down Expand Up @@ -555,7 +555,7 @@ Score SearchHandler::quiescent_search(const Position& old_pos, Score alpha, Scor
const auto raw_eval = [&]() {
if (old_pos.in_check()) {
return MagicNumbers::NegativeInfinity;
} else if (tt_hit && entry->get().static_eval() > (MagicNumbers::NegativeInfinity + MAX_PLY)) {
} else if (tt_hit && entry->get().static_eval() > MATED_IN_MAX_PLY) {
return entry->get().static_eval();
} else {
return Evaluation::evaluate_board(old_pos);
Expand Down Expand Up @@ -588,7 +588,7 @@ Score SearchHandler::quiescent_search(const Position& old_pos, Score alpha, Scor
Move best_move = Move::NULL_MOVE();
std::optional<ScoredMove> opt_move;
auto found_move = false;
while ((opt_move = mp.next(best_score > (MagicNumbers::NegativeInfinity + MAX_PLY))).has_value()) {
while ((opt_move = mp.next(best_score > MATED_IN_MAX_PLY)).has_value()) {
if (search_cancelled) {
break;
}
Expand Down Expand Up @@ -716,7 +716,7 @@ Move SearchHandler::run_iterative_deepening_search() {
if (!search_cancelled && print_info) {
const auto nps = static_cast<uint64_t>(node_count / (static_cast<float>(time_so_far) / 1000));
fmt::print("info depth {} nodes {} nps {} score ", depth, node_count, nps);
if ((std::abs(current_score) >= (MagicNumbers::PositiveInfinity - MAX_PLY))) {
if ((std::abs(current_score) >= MATE_IN_MAX_PLY)) {
fmt::print("mate {} ", ((current_score / std::abs(current_score)) * (depth + 1)) / 2);
} else {
fmt::print("cp {} ", current_score);
Expand All @@ -728,7 +728,7 @@ Move SearchHandler::run_iterative_deepening_search() {
fmt::println("");
}

if (current_score >= (MagicNumbers::PositiveInfinity - MAX_PLY)) {
if (current_score >= MATE_IN_MAX_PLY) {
return pv_move;
}

Expand Down
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