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Enable bidirectional optimization for non-common ranges in std::ranges::partition #5887

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Merged
merged 1 commit into from
Nov 27, 2025
+8 −7
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Enable bidirectional optimization for non-common ranges in std::ranges::partition #5887

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15 changes: 8 additions & 7 deletions stl/inc/algorithm
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Original file line number Diff line number Diff line change
Expand Up @@ -6986,11 +6986,12 @@ namespace ranges {
_STL_INTERNAL_STATIC_ASSERT(sentinel_for<_Se, _It>);
_STL_INTERNAL_STATIC_ASSERT(indirect_unary_predicate<_Pr, projected<_It, _Pj>>);

if constexpr (_Bidi_common<_It, _Se>) {
auto _Saved_last = _Last;
if constexpr (bidirectional_iterator<_It>) {
auto _Saved_last = _RANGES next(_First, _Last);
auto _Tail = _Saved_last;
for (;; ++_First) { // find any out-of-order pair
for (;; ++_First) { // skip in-place elements at beginning
if (_First == _Last) {
if (_First == _Tail) {
return {_STD move(_First), _STD move(_Saved_last)};
}

Expand All @@ -7000,13 +7001,13 @@ namespace ranges {
}

do { // skip in-place elements at end
--_Last;
if (_First == _Last) {
--_Tail;
if (_First == _Tail) {
return {_STD move(_First), _STD move(_Saved_last)};
}
} while (!_STD invoke(_Pred, _STD invoke(_Proj, *_Last)));
} while (!_STD invoke(_Pred, _STD invoke(_Proj, *_Tail)));

_RANGES iter_swap(_First, _Last); // out of place, swap and loop
_RANGES iter_swap(_First, _Tail); // out of place, swap and loop
}

return {_STD move(_First), _STD move(_Saved_last)};
Expand Down