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Add post-LMR continuation history updates #29

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Merged
KnightStackSys merged 1 commit into from
Oct 13, 2026
Merged

Add post-LMR continuation history updates #29

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30 changes: 29 additions & 1 deletion src/search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,10 @@ namespace ironphoenix {
constexpr int HISTORY_MOVE_PRUNE_MAX_DEPTH = 4;
constexpr int HISTORY_MOVE_PRUNE_MARGIN_PER_DEPTH = 1'500;

// Post-LMR continuation history: reward a reduced quiet move that proves
// strong enough to beat alpha and require a full-depth re-search.
constexpr int POST_LMR_CONTINUATION_BONUS = 1'334;

constexpr int NULL_MOVE_MIN_DEPTH = 2;
constexpr int NULL_MOVE_DIVISOR = 190;
constexpr std::size_t CHECK_BIT_WORDS = (MAX_MOVES + 63u) / 64u;
Expand Down Expand Up @@ -716,8 +720,32 @@ namespace ironphoenix {
const int reducedDepth = depth - 1 - reduction;
score = -negamax(pos, reducedDepth, -alpha - 1, -alpha, ply + 1, false);

if (!shouldStop() && score > alpha)
if (!shouldStop() && score > alpha) {
// Post-LMR continuation-history update: the move was
// reduced because it looked unpromising, but the
// reduced search still beat alpha. Reward the
// continuation contexts before the full-depth retry.
if (ply > 0 && searchStack_[ply].valid()) {
history_.updateContinuation(
ContinuationKind::PreviousPly,
searchStack_[ply],
movingPiece,
move.to(),
POST_LMR_CONTINUATION_BONUS);
}

if (ply >= 4 && searchStack_[ply - 3].valid()
&& searchStack_[ply - 3].mover == us) {
history_.updateContinuation(
ContinuationKind::SamePlayer,
searchStack_[ply - 3],
movingPiece,
move.to(),
(POST_LMR_CONTINUATION_BONUS * 3) / 4);
}

score = -negamax(pos, depth - 1, -alpha - 1, -alpha, ply + 1, false);
}
}
else {
score = -negamax(pos, depth - 1, -alpha - 1, -alpha, ply + 1, false);
Expand Down