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Partial insertion sort

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the order of elements returned by std::partition is implementation defined (since not stable) and could depend on the version of libstdc++ linked.
As std::stable_partition was tested to be too slow (http://tests.stockfishchess.org/tests/view/585cdfd00ebc5903140c6082).
Instead combine partition with our custom implementation of insert_sort, which fixes this issue.
Implementation based on a patch by mstembera (http://tests.stockfishchess.org/tests/view/58d4d3460ebc59035df3315c), which suggests some benefit by itself.
Higher depth moves are all sorted (INT_MIN version), as in current master.

STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 33116 W: 6161 L: 6061 D: 20894

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 88703 W: 11572 L: 11540 D: 65591

Bench: 6256522

Closes #1058
Closes #1065
This commit is contained in:
Joost VandeVondele 2017-04-20 11:15:48 -07:00 • committed by Joona Kiiski
parent d4b9ee0f1d
commit 2d96e8fbe9
1 changed files with 17 additions and 18 deletions
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27
src/movepick.cpp
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@ -34,17 +34,20 @@ namespace {
QSEARCH_RECAPTURES, QRECAPTURES
};
// Our insertion sort, which is guaranteed to be stable, as it should be
void insertion_sort(ExtMove* begin, ExtMove* end)
// An insertion sort, which sorts moves in descending order up to and including a given limit.
// The order of moves smaller than the limit is left unspecified.
// To keep the implementation simple, *begin is always included in the list of sorted moves.
void partial_insertion_sort(ExtMove* begin, ExtMove* end, Value limit)
{
ExtMove tmp, *p, *q;
for (p = begin + 1; p < end; ++p)
for (ExtMove *sortedEnd = begin + 1, *p = begin + 1; p < end; ++p)
if (p->value >= limit)
{
tmp = *p;
for (q = p; q != begin && *(q-1) < tmp; --q)
ExtMove tmp = *p, *q;
*p = *sortedEnd;
for (q = sortedEnd; q != begin && *(q-1) < tmp; --q)
*q = *(q-1);
*q = tmp;
++sortedEnd;
}
}
@ -238,13 +241,9 @@ Move MovePicker::next_move(bool skipQuiets) {
cur = endBadCaptures;
endMoves = generate<QUIETS>(pos, cur);
score<QUIETS>();
if (depth < 3 * ONE_PLY)
{
ExtMove* goodQuiet = std::partition(cur, endMoves, [](const ExtMove& m)
{ return m.value > VALUE_ZERO; });
insertion_sort(cur, goodQuiet);
} else
insertion_sort(cur, endMoves);
partial_insertion_sort(cur, endMoves,
depth < 3 * ONE_PLY ? VALUE_ZERO : Value(INT_MIN));
++stage;
case QUIET: