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Extend stack to ss-5, and remove conditions

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The `&& (ss-1)->killers[0] ` conditions are there seemingly to protect
accessing ss-5.

This is unneeded and not so intuitive (as the killer is checked for equality
with currentMove, and that one is non-zero once we're high enough in the stack,
this protects access to ss-5). We can just extend the stack from ss-4 to ss-5,
so we can call update_continuation_histories(ss-1, ..) always in search.

This goes a bit further than #1881 and addresses a comment in #1878.

passed STC:
http://tests.stockfishchess.org/tests/view/5c1aa8d50ebc5902ba127ad0
LLR: 3.12 (-2.94,2.94) [-3.00,1.00]
Total: 53515 W: 11734 L: 11666 D: 30115

passed LTC:
http://tests.stockfishchess.org/tests/view/5c1b272c0ebc5902ba12858d
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 140176 W: 23123 L: 23192 D: 93861

Bench: 3451321
This commit is contained in:
Joost VandeVondele 2018-12-19 21:04:36 +01:00 • committed by Stéphane Nicolet
parent 96ac85b319
commit ade87ff8d3
1 changed files with 12 additions and 11 deletions
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23
src/search.cpp
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@ -303,7 +303,11 @@ void MainThread::search() {
void Thread::search() {
Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2)
// To allow access to (ss-5) up to (ss+2), the stack must be oversized.
// The former is needed to allow update_continuation_histories(ss-1, ...),
// which accesses its argument at ss-4, also near the root.
// The latter is needed for statScores and killer initialization.
Stack stack[MAX_PLY+8], *ss = stack+5;
Move pv[MAX_PLY+1];
Value bestValue, alpha, beta, delta;
Move lastBestMove = MOVE_NONE;
@ -313,8 +317,8 @@ void Thread::search() {
Color us = rootPos.side_to_move();
bool failedLow;
std::memset(ss-4, 0, 7 * sizeof(Stack));
for (int i = 4; i > 0; i--)
std::memset(ss-5, 0, 8 * sizeof(Stack));
for (int i = 5; i > 0; i--)
(ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel
ss->pv = pv;
@ -657,9 +661,8 @@ namespace {
update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
// Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
if ( (ss-1)->moveCount == 1
|| ((ss-1)->currentMove == (ss-1)->killers[0] && (ss-1)->killers[0]))
if (!pos.captured_piece())
if ( ((ss-1)->moveCount == 1 || (ss-1)->currentMove == (ss-1)->killers[0])
&& !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
}
// Penalty for a quiet ttMove that fails low
@ -1192,16 +1195,14 @@ moves_loop: // When in check, search starts from here
update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
// Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
if ( (ss-1)->moveCount == 1
|| ((ss-1)->currentMove == (ss-1)->killers[0] && (ss-1)->killers[0]))
if (!pos.captured_piece())
if ( ((ss-1)->moveCount == 1 || ((ss-1)->currentMove == (ss-1)->killers[0]))
&& !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
}
// Bonus for prior countermove that caused the fail low
else if ( (depth >= 3 * ONE_PLY || PvNode)
&& !pos.captured_piece()
&& is_ok((ss-1)->currentMove))
&& !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
if (PvNode)