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Restore wmemchr optimization in ranges::find #5628

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Merged
merged 6 commits into from
Jul 15, 2025
+28 −19
Merged

Restore wmemchr optimization in ranges::find #5628

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e3ce518
Restore wmemchr optimization
AlexGuteniev Jun 16, 2025
cf3a333
casts
AlexGuteniev Jul 1, 2025
3f19232
fix nullptr
AlexGuteniev Jul 2, 2025
296b0e2
Refactor for clarity: 1 byte, 2 bytes, more bytes.
StephanTLavavej Jul 10, 2025
6956443
Update comment for memchr()/wmemchr().
StephanTLavavej Jul 10, 2025
1b0758e
Extract null handling.
StephanTLavavej Jul 10, 2025
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47 changes: 30 additions & 17 deletions stl/inc/xutility
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Original file line number Diff line number Diff line change
Expand Up @@ -6266,12 +6266,13 @@ namespace ranges {
template <input_iterator _It, sentinel_for<_It> _Se, class _Ty, class _Pj = identity>
requires indirect_binary_predicate<ranges::equal_to, projected<_It, _Pj>, const _Ty*>
_NODISCARD constexpr _It _Find_unchecked(_It _First, const _Se _Last, const _Ty& _Val, _Pj _Proj = {}) {
constexpr bool _Elements_are_1_byte = sizeof(_Iter_value_t<_It>) == 1;
constexpr bool _Is_sized = sized_sentinel_for<_Se, _It>;
constexpr bool _Elements_are_1_byte = sizeof(_Iter_value_t<_It>) == 1;
constexpr bool _Elements_are_2_bytes = sizeof(_Iter_value_t<_It>) == 2;
constexpr bool _Is_sized = sized_sentinel_for<_Se, _It>;

if constexpr (_Vector_alg_in_find_is_safe<_It, _Ty>
&& (_Elements_are_1_byte ? _Is_sized || same_as<_Se, unreachable_sentinel_t>
: _Is_sized && _USE_STD_VECTOR_ALGORITHMS)
: _Is_sized && (_Elements_are_2_bytes || _USE_STD_VECTOR_ALGORITHMS))
&& same_as<_Pj, identity>) {
if (!_STD is_constant_evaluated()) {
if (!_STD _Could_compare_equal_to_value_type<_It>(_Val)) {
Expand All @@ -6295,24 +6296,36 @@ namespace ranges {
} else
#endif // ^^^ _USE_STD_VECTOR_ALGORITHMS ^^^
{
_STL_INTERNAL_STATIC_ASSERT(_Elements_are_1_byte);
size_t _Count;
if constexpr (_Is_sized) {
_Count = static_cast<size_t>(_Last - _First);
} else {
_Count = SIZE_MAX;
}
if constexpr (_Elements_are_2_bytes) {
_STL_INTERNAL_STATIC_ASSERT(_Is_sized);
_Result = reinterpret_cast<_Ptr_t>(
const_cast<wchar_t*>(_CSTD wmemchr(reinterpret_cast<const wchar_t*>(_First_ptr),
static_cast<wchar_t>(_Val), static_cast<size_t>(_Last - _First))));

// C23 7.27.5.2 "The memchr generic function"/2 says "The implementation shall behave as if
// it reads the characters sequentially and stops as soon as a matching character is found."
// C23 7.32.4.6.9 "The wmemchr generic function"/2 lacks such wording,
// so we don't use wmemchr(), avoiding issues with unreachable_sentinel_t.
_Result = static_cast<_Ptr_t>(_CSTD memchr(_First_ptr, static_cast<unsigned char>(_Val), _Count));

if constexpr (_Is_sized) {
if (_Result == nullptr) {
return _RANGES next(_STD move(_First), _Last);
}
} else {
_STL_INTERNAL_STATIC_ASSERT(_Elements_are_1_byte);
size_t _Count;
if constexpr (_Is_sized) {
_Count = static_cast<size_t>(_Last - _First);
} else {
_Count = SIZE_MAX;
}

// C23 7.27.5.2 "The memchr generic function"/2 says "The implementation shall behave as if
// it reads the characters sequentially and stops as soon as a matching character is found."
// C23 7.32.4.6.9 "The wmemchr generic function"/2 lacks such wording,
// so we don't use wmemchr(), avoiding issues with unreachable_sentinel_t.
_Result =
static_cast<_Ptr_t>(_CSTD memchr(_First_ptr, static_cast<unsigned char>(_Val), _Count));

if constexpr (_Is_sized) {
if (_Result == nullptr) {
return _RANGES next(_STD move(_First), _Last);
}
}
}
}

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