================
@@ -428,50 +653,60 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp,
_Allocator>::shrink_to_fi
}
}
-template <class _Tp, class _Allocator>
+template <class _Tp, class _Allocator, template <class, class, class> class
_Layout>
template <class... _Args>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp,
_Allocator>::emplace_front(_Args&&... __args) {
- if (__begin_ == __first_) {
- if (__end_ < __cap_) {
- difference_type __d = __cap_ - __end_;
+_LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator,
_Layout>::emplace_front(_Args&&... __args) {
+ if (__front_spare() == 0) {
+ pointer __end = end();
+ if (__back_spare() > 0) {
+ // The elements are pressed up against the front of the buffer: we need
to move them back a
+ // little bit to make `emplace_front` have amortised O(1) complexity.
+ difference_type __d = __back_spare();
__d = (__d + 1) / 2;
- __begin_ = std::move_backward(__begin_, __end_, __end_ + __d);
- __end_ += __d;
+ __set_begin(std::move_backward(begin(), __end, __end + __d));
+
+ // `begin()` was moved further into the buffer, so we need to update the
pointer-based
+ // layout's end with it. We don't need to do anything for the size-based
layout here, because
+ // the number of elements hasn't changed yet.
+ __set_size_if_pointer_based(__d);
} else {
- size_type __c = std::max<size_type>(2 * static_cast<size_type>(__cap_ -
__first_), 1);
- __split_buffer<value_type, __alloc_rr&> __t(__c, (__c + 3) / 4,
__alloc_);
- __t.__construct_at_end(move_iterator<pointer>(__begin_),
move_iterator<pointer>(__end_));
- std::swap(__first_, __t.__first_);
- std::swap(__begin_, __t.__begin_);
- std::swap(__end_, __t.__end_);
- std::swap(__cap_, __t.__cap_);
+ size_type __c = std::max<size_type>(2 * capacity(), 1);
+ __split_buffer<value_type, __alloc_rr&> __t(__c, (__c + 3) / 4,
this->__alloc_);
+ __t.__construct_at_end(move_iterator<pointer>(begin()),
move_iterator<pointer>(__end));
+ __swap_without_allocator(__t);
}
}
- __alloc_traits::construct(__alloc_, std::__to_address(__begin_ - 1),
std::forward<_Args>(__args)...);
- --__begin_;
+
+ __alloc_traits::construct(this->__alloc_, std::__to_address(begin() - 1),
std::forward<_Args>(__args)...);
+ __set_begin(begin() - 1);
+
+ // Now that we've added an element to the front of the buffer, we need to
update the size-based
+ // layout's size. We don't need to do anything for the pointer-based layout
here, because the end
+ // pointer was never updated.
+ __set_end_if_size_based();
----------------
cjdb wrote:
Done. I agree that combining `__set_begin` and `__set_sentinel` is a good move.
https://github.com/llvm/llvm-project/pull/139632
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