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Replace complex probcut function with a precomputed table.

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Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/680de2683629b02d74b15b46
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 116000 W: 29864 L: 29742 D: 56394
Ptnml(0-2): 215, 11811, 33854, 11877, 243

closes https://github.com/official-stockfish/Stockfish/pull/6026

No functional change
This commit is contained in:
Myself
2025-04-27 14:52:01 +07:00
committed by Disservin
parent b0a7a34d3f
commit 37cc2293ef
1 changed files with 4 additions and 10 deletions
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14
src/search.cpp
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@@ -111,17 +111,11 @@ Value to_corrected_static_eval(const Value v, const int cv) {
return std::clamp(v + cv / 131072, VALUE_TB_LOSS_IN_MAX_PLY + 1, VALUE_TB_WIN_IN_MAX_PLY - 1);
}
int adaptive_probcut_margin(Depth depth) {
// Base margin
constexpr int base = 180;
// Approximate log2(depth) using a fast lookup table
static constexpr int logTable[32] = {0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4};
constexpr int adaptiveProbcutMargin[32] = {148, 150, 212, 214, 276, 278, 280, 282, 344, 346, 348,
350, 352, 354, 356, 358, 420, 422, 424, 426, 428, 430,
430, 430, 430, 430, 430, 430, 430, 430, 430, 430};
int logDepth = logTable[std::min(depth, 31)];
return base + logDepth * 60 + std::min(10, (depth - 16) * 2);
};
void update_correction_history(const Position& pos,
Stack* const ss,
@@ -994,7 +988,7 @@ Value Search::Worker::search(
moves_loop: // When in check, search starts here
// Step 12. A small Probcut idea
probCutBeta = beta + adaptive_probcut_margin(depth);
probCutBeta = beta + adaptiveProbcutMargin[std::min(depth, 31)];
if ((ttData.bound & BOUND_LOWER) && ttData.depth >= depth - 4 && ttData.value >= probCutBeta
&& !is_decisive(beta) && is_valid(ttData.value) && !is_decisive(ttData.value))
return probCutBeta;