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Use stable sort to make sure bench with TB yields same results everywhere.

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std::sort() is not stable so different implementations can produce different results:
use the stable version instead.

Observed for '8/6k1/5r2/8/8/8/1K6/Q7 w - - 0 1' yielding different bench results for gcc and MSVC
and 3-4-5 syzygy TB prior to this patch.

closes https://github.com/official-stockfish/Stockfish/pull/3083

No functional change.
This commit is contained in:
mstembera 2020-08-30 18:40:49 -07:00 • committed by Joost VandeVondele
parent e0bafa1911
commit a0afe32d16
2 changed files with 3 additions and 3 deletions
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2
src/search.cpp
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@ -1964,7 +1964,7 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
if (RootInTB)
{
// Sort moves according to TB rank
std::sort(rootMoves.begin(), rootMoves.end(),
std::stable_sort(rootMoves.begin(), rootMoves.end(),
[](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } );
// Probe during search only if DTZ is not available and we are winning

4
src/syzygy/tbprobe.cpp
View file

@ -758,7 +758,7 @@ Ret do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* resu
if (entry->hasPawns) {
idx = LeadPawnIdx[leadPawnsCnt][squares[0]];
std::sort(squares + 1, squares + leadPawnsCnt, pawns_comp);
std::stable_sort(squares + 1, squares + leadPawnsCnt, pawns_comp);
for (int i = 1; i < leadPawnsCnt; ++i)
idx += Binomial[i][MapPawns[squares[i]]];
@ -859,7 +859,7 @@ encode_remaining:
while (d->groupLen[++next])
{
std::sort(groupSq, groupSq + d->groupLen[next]);
std::stable_sort(groupSq, groupSq + d->groupLen[next]);
uint64_t n = 0;
// Map down a square if "comes later" than a square in the previous