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<xstring>: Use memmove in construction of basic_string when the source is a suitable contiguous range #4073

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merged 6 commits into from
Oct 14, 2023
Merged

<xstring>: Use memmove in construction of basic_string when the source is a suitable contiguous range #4073

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057df3d
Use `memcpy` in the iterator-pair construction of `basic_string`
frederick-vs-ja Oct 6, 2023
c434395
Fix typos, one major.
StephanTLavavej Oct 6, 2023
55c74e2
Tweak comments for preconditions of `_Construct_from_iter`
frederick-vs-ja Oct 7, 2023
67d11b6
Reuse `_Copy_n_unchecked4` (which calls `memmove`)
frederick-vs-ja Oct 9, 2023
3fddbf5
Locally suppress warning C4365
frederick-vs-ja Oct 10, 2023
da953f8
Move the suppression to the test
frederick-vs-ja Oct 10, 2023
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60 changes: 37 additions & 23 deletions stl/inc/xstring
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Original file line number Diff line number Diff line change
Expand Up @@ -2695,10 +2695,12 @@ private:

template <class _Iter, class _Sent, class _Size = nullptr_t>
_CONSTEXPR20 void _Construct_from_iter(_Iter _First, const _Sent _Last, _Size _Count = {}) {
// Pre: _First models input_iterator or meets the Cpp17InputIterator requirements
// Pre: [_First, _Last) is a valid range
// Pre: _Iter models input_iterator or meets the Cpp17InputIterator requirements.
// Pre: [_First, _Last) is a valid range.
// Pre: if _Iter models forward_iterator or meets the Cpp17ForwardIterator requirements,
// then is_same_v<_Size, size_type> holds.
// Pre: if is_same_v<_Size, size_type>, _Count is the length of [_First, _Last).
// Pre: *this is in small mode; the lifetime of the SSO elements has already begun
// Pre: *this is in small mode; the lifetime of the SSO elements has already begun.

auto& _My_data = _Mypair._Myval2;
auto& _Al = _Getal();
Expand All @@ -2722,35 +2724,47 @@ private:
}

_Tidy_deallocate_guard<basic_string> _Guard{this};
for (; _First != _Last; ++_First) {
if constexpr (!is_same_v<_Size, size_type>) {
if (_My_data._Mysize == _My_data._Myres) { // Need to grow
if (_My_data._Mysize == max_size()) {
_Xlen_string(); // result too long
}

_Elem* const _Old_ptr = _My_data._Myptr();
size_type _New_capacity = _Calculate_growth(_My_data._Mysize + 1);
const pointer _New_ptr = _Allocate_for_capacity(_Al, _New_capacity); // throws
constexpr bool _Can_construct_by_copy =
_Is_specialization_v<_Traits, char_traits> && _Is_EcharT<_Elem> && is_same_v<_Size, size_type>;

_Traits::copy(_Unfancy(_New_ptr), _Old_ptr, _My_data._Mysize);
if (_My_data._Large_mode_engaged()) { // Need to deallocate old storage
_Deallocate_for_capacity(_Al, _My_data._Bx._Ptr, _My_data._Myres);
_My_data._Bx._Ptr = _New_ptr;
} else {
_Construct_in_place(_My_data._Bx._Ptr, _New_ptr);
if constexpr (_Can_construct_by_copy) {
const auto _Data = _My_data._Myptr();
_STD _Copy_n_unchecked4(_STD move(_First), _Count, _Data);
_My_data._Mysize = _Count;
_Data[_Count] = _Elem();
} else {
for (; _First != _Last; ++_First) {
if constexpr (!is_same_v<_Size, size_type>) {
if (_My_data._Mysize == _My_data._Myres) { // Need to grow
if (_My_data._Mysize == max_size()) {
_Xlen_string(); // result too long
}

_Elem* const _Old_ptr = _My_data._Myptr();
size_type _New_capacity = _Calculate_growth(_My_data._Mysize + 1);
const pointer _New_ptr = _Allocate_for_capacity(_Al, _New_capacity); // throws

_Traits::copy(_Unfancy(_New_ptr), _Old_ptr, _My_data._Mysize);
if (_My_data._Large_mode_engaged()) { // Need to deallocate old storage
_Deallocate_for_capacity(_Al, _My_data._Bx._Ptr, _My_data._Myres);
_My_data._Bx._Ptr = _New_ptr;
} else {
_Construct_in_place(_My_data._Bx._Ptr, _New_ptr);
}
_My_data._Myres = _New_capacity;
}
_My_data._Myres = _New_capacity;
}

_Elem* const _Ptr = _My_data._Myptr();
_Traits::assign(_Ptr[_My_data._Mysize], *_First);
++_My_data._Mysize;
}

_Elem* const _Ptr = _My_data._Myptr();
_Traits::assign(_Ptr[_My_data._Mysize], *_First);
++_My_data._Mysize;
_Traits::assign(_Ptr[_My_data._Mysize], _Elem());
}

_Elem* const _Ptr = _My_data._Myptr();
_Traits::assign(_Ptr[_My_data._Mysize], _Elem());
_ASAN_STRING_CREATE(*this);
_Guard._Target = nullptr;
_Proxy._Release();
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