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#pragma once
#include "asl/meta.hpp"
#include "asl/allocator.hpp"
#include "asl/annotations.hpp"
#include "asl/memory.hpp"
#include "asl/assert.hpp"
namespace asl
{
template<is_object T, allocator Allocator = DefaultAllocator>
class buffer
{
T* m_data{};
isize_t m_capacity{};
public:
static constexpr isize_t kInlineCapacity = []() {
// 1 byte is used for size inline in m_size_encoded.
// This is enough because we have at most 24 bytes available,
// so 23 chars of capacity.
const isize_t available_size = size_of<T*> + size_of<isize_t> + size_of<size_t> - 1;
return available_size / size_of<T>;
}();
private:
static constexpr size_t kOnHeapMask = 0x8000'0000'0000'0000ULL;
// bit 63 : 1 = on heap, 0 = inline
// bits [62:56] : size when inline
// bits [62:0] : size when on heap
size_t m_size_encoded_{};
ASL_NO_UNIQUE_ADDRESS Allocator m_allocator;
static_assert(align_of<T> <= align_of<T*>);
static_assert(align_of<T*> == align_of<isize_t>);
static_assert(align_of<T*> == align_of<size_t>);
constexpr size_t load_size_encoded() const
{
size_t s{};
asl::memcpy(&s, &m_size_encoded_, sizeof(size_t));
return s;
}
constexpr void store_size_encoded(size_t encoded)
{
asl::memcpy(&m_size_encoded_, &encoded, sizeof(size_t));
}
static constexpr bool is_on_heap(size_t size_encoded)
{
return (size_encoded & kOnHeapMask) != 0;
}
static constexpr size_t encode_size_heap(isize_t size)
{
return static_cast<size_t>(size) | kOnHeapMask;
}
static constexpr isize_t decode_size(size_t size_encoded)
{
if constexpr (kInlineCapacity == 0)
{
return is_on_heap(size_encoded)
? static_cast<isize_t>(size_encoded & (~kOnHeapMask))
: 0;
}
else
{
return is_on_heap(size_encoded)
? static_cast<isize_t>(size_encoded & (~kOnHeapMask))
: static_cast<isize_t>(size_encoded >> 56);
}
}
constexpr bool is_on_heap() const
{
return is_on_heap(load_size_encoded());
}
constexpr T* push_uninit()
{
isize_t sz = size();
reserve_capacity(sz + 1);
set_size(sz + 1);
return data() + sz;
}
constexpr void set_size(isize_t new_size)
{
ASL_ASSERT(new_size >= 0);
ASL_ASSERT_RELEASE(new_size <= capacity());
size_t size_encoded = load_size_encoded();
if (kInlineCapacity == 0 || is_on_heap(size_encoded))
{
store_size_encoded(encode_size_heap(new_size));
}
else
{
ASL_ASSERT(new_size <= kInlineCapacity);
size_encoded = (size_encoded & size_t{0x00ff'ffff'ffff'ffff}) | (bit_cast<size_t>(new_size) << 56);
store_size_encoded(size_encoded);
}
}
public:
constexpr buffer() requires default_constructible<Allocator> = default;
explicit constexpr buffer(Allocator allocator)
: m_allocator{ASL_MOVE(allocator)}
{}
constexpr isize_t size() const
{
return decode_size(load_size_encoded());
}
constexpr isize_t capacity() const
{
if constexpr (kInlineCapacity == 0)
{
return m_capacity;
}
else
{
return is_on_heap() ? m_capacity : kInlineCapacity;
}
}
void reserve_capacity(isize_t new_capacity)
{
ASL_ASSERT(new_capacity >= 0);
ASL_ASSERT_RELEASE(new_capacity <= 0x4000'0000'0000'0000);
if (new_capacity <= capacity()) { return; }
ASL_ASSERT(new_capacity > kInlineCapacity);
new_capacity = static_cast<isize_t>(round_up_pow2(static_cast<uint64_t>(new_capacity)));
T* old_data = data();
const isize_t old_capacity = capacity();
const isize_t current_size = size();
const bool currently_on_heap = is_on_heap();
auto old_layout = layout::array<T>(old_capacity);
auto new_layout = layout::array<T>(new_capacity);
if (currently_on_heap && trivially_copyable<T>)
{
m_data = reinterpret_cast<T*>(m_allocator.realloc(m_data, old_layout, new_layout));
m_capacity = new_capacity;
return;
}
T* new_data = reinterpret_cast<T*>(m_allocator.alloc(new_layout));
relocate_uninit_n(new_data, old_data, current_size);
if (currently_on_heap)
{
m_allocator.dealloc(old_data, old_layout);
}
m_data = new_data;
m_capacity = new_capacity;
store_size_encoded(encode_size_heap(current_size));
}
constexpr T& push(auto&&... args)
requires constructible_from<T, decltype(args)&&...>
{
T* uninit = push_uninit();
T* init = construct_at<T>(uninit, ASL_FWD(args)...);
return *init;
}
// @Todo(C++23) Use deducing this
const T* data() const
{
if constexpr (kInlineCapacity == 0)
{
return m_data;
}
else
{
return is_on_heap() ? m_data : reinterpret_cast<const T*>(this);
}
}
T* data()
{
if constexpr (kInlineCapacity == 0)
{
return m_data;
}
else
{
return is_on_heap() ? m_data : reinterpret_cast<T*>(this);
}
}
// @Todo operator[]
};
} // namespace asl
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