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Reintroduce razoring

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Razoring was simplified away some years ago, this patch reintroduces it in a slightly different form.
Now for low depths if eval is far below alpha we check if qsearch can push it above alpha - and if it can't we return a fail low.

passed STC
https://tests.stockfishchess.org/tests/view/61fbf968d508ec6a1c9f3274
LLR: 2.94 (-2.94,2.94) <0.00,2.50>
Total: 226120 W: 61106 L: 60472 D: 104542
Ptnml(0-2): 1118, 25592, 59080, 26078, 1192

passed LTC
https://tests.stockfishchess.org/tests/view/61fcc569d508ec6a1c9f5617
LLR: 2.94 (-2.94,2.94) <0.50,3.00>
Total: 113128 W: 30851 L: 30397 D: 51880
Ptnml(0-2): 114, 11483, 32926, 11917, 124

closes https://github.com/official-stockfish/Stockfish/pull/3921

bench 4684080
This commit is contained in:
Michael Chaly 2022-02-05 04:03:02 +03:00 • committed by Joost VandeVondele
parent 95d7369e54
commit 4d3950c6eb
1 changed files with 24 additions and 14 deletions
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38
src/search.cpp
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@ -773,7 +773,17 @@ namespace {
thisThread->complexityAverage.update(complexity);
// Step 7. Futility pruning: child node (~25 Elo).
// Step 7. Razoring.
// If eval is really low check with qsearch if it can exceed alpha, if it can't,
// return a fail low.
if (!PvNode && depth <= 6 && eval < alpha - 400 - 300 * depth * depth)
{
value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
if (value < alpha)
return value;
}
// Step 8. Futility pruning: child node (~25 Elo).
// The depth condition is important for mate finding.
if ( !ss->ttPv
&& depth < 9
@ -782,7 +792,7 @@ namespace {
&& eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
return eval;
// Step 8. Null move search with verification search (~22 Elo)
// Step 9. Null move search with verification search (~22 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
&& (ss-1)->statScore < 23767
@ -834,7 +844,7 @@ namespace {
probCutBeta = beta + 209 - 44 * improving;
// Step 9. ProbCut (~4 Elo)
// Step 10. ProbCut (~4 Elo)
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
@ -895,7 +905,7 @@ namespace {
ss->ttPv = ttPv;
}
// Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type (~3 Elo)
// Step 11. If the position is not in TT, decrease depth by 2 or 1 depending on node type (~3 Elo)
if ( PvNode
&& depth >= 6
&& !ttMove)
@ -908,7 +918,7 @@ namespace {
moves_loop: // When in check, search starts here
// Step 11. A small Probcut idea, when we are in check (~0 Elo)
// Step 12. A small Probcut idea, when we are in check (~0 Elo)
probCutBeta = beta + 409;
if ( ss->inCheck
&& !PvNode
@ -945,7 +955,7 @@ moves_loop: // When in check, search starts here
&& (tte->bound() & BOUND_UPPER)
&& tte->depth() >= depth;
// Step 12. Loop through all pseudo-legal moves until no moves remain
// Step 13. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{
@ -985,7 +995,7 @@ moves_loop: // When in check, search starts here
Value delta = beta - alpha;
// Step 13. Pruning at shallow depth (~98 Elo). Depth conditions are important for mate finding.
// Step 14. Pruning at shallow depth (~98 Elo). Depth conditions are important for mate finding.
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
@ -1038,7 +1048,7 @@ moves_loop: // When in check, search starts here
}
}
// Step 14. Extensions (~66 Elo)
// Step 15. Extensions (~66 Elo)
// We take care to not overdo to avoid search getting stuck.
if (ss->ply < thisThread->rootDepth * 2)
{
@ -1115,12 +1125,12 @@ moves_loop: // When in check, search starts here
[movedPiece]
[to_sq(move)];
// Step 15. Make the move
// Step 16. Make the move
pos.do_move(move, st, givesCheck);
bool doDeeperSearch = false;
// Step 16. Late moves reduction / extension (LMR, ~98 Elo)
// Step 17. Late moves reduction / extension (LMR, ~98 Elo)
// We use various heuristics for the sons of a node after the first son has
// been searched. In general we would like to reduce them, but there are many
// cases where we extend a son if it has good chances to be "interesting".
@ -1188,7 +1198,7 @@ moves_loop: // When in check, search starts here
didLMR = false;
}
// Step 17. Full depth search when LMR is skipped or fails high
// Step 18. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
@ -1218,12 +1228,12 @@ moves_loop: // When in check, search starts here
std::min(maxNextDepth, newDepth), false);
}
// Step 18. Undo move
// Step 19. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// Step 19. Check for a new best move
// Step 20. Check for a new best move
// Finished searching the move. If a stop occurred, the return value of
// the search cannot be trusted, and we return immediately without
// updating best move, PV and TT.
@ -1306,7 +1316,7 @@ moves_loop: // When in check, search starts here
return VALUE_DRAW;
*/
// Step 20. Check for mate and stalemate
// Step 21. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it
// must be a mate or a stalemate. If we are in a singular extension search then
// return a fail low score.