libcruft-util/alloc/raw/aligned/foreign.hpp
Danny Robson c2265b9ed2 alloc: add aligned::foreign allocator
sometimes we need to ensure memory allocation has a particular alignment
in an _offset_ buffer (which we have no control over, eg renderdoc's
OpenGL buffers).

this applies an offset to various operations that make the
aligned::direct allocator correctly align allocations for buffers that
aren't themselves aligned.
2018-03-02 12:21:38 +11:00

100 lines
3.2 KiB
C++

/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2016 Danny Robson <danny@nerdcruft.net>
*/
#ifndef CRUFT_UTIL_ALLOC_RAW_ALIGNED_OFFSET_HPP
#define CRUFT_UTIL_ALLOC_RAW_ALIGNED_OFFSET_HPP
#include "direct.hpp"
#include "../../../pointer.hpp"
#include "../../../debug.hpp"
#include <cstddef>
#include <utility>
namespace util::alloc::raw::aligned {
/// wraps a child allocator and enforces a fixed alignment that is
/// independant of the alignment of the provided source buffer.
///
/// we use the approach of:
/// * shifting the source buffer's alignment to satisfy the requested
/// alignment
/// * using a direct alignment child to service the requests
/// * then applying the reverse offset to values as we return the values
template <typename ChildT>
class foreign {
public:
template <typename ...Args>
foreign (util::view<std::byte*> _data, std::size_t _alignment, Args &&...args):
m_successor (
view<std::byte*> {0, _data.size ()},
_alignment,
std::forward<Args> (args)...
),
m_offset (m_successor.data () - _data.data ()),
m_alignment (_alignment)
{ ; }
void*
allocate (std::size_t size)
{
auto ptr= reinterpret_cast<std::byte*> (
m_successor.allocate (size)
);
return ptr - m_offset;
}
auto
deallocate (void *ptr, std::size_t size)
{
return m_successor.deallocate (
reinterpret_cast<std::byte*> (ptr) + m_offset, size
);
}
constexpr auto alignment (void) const noexcept { return m_alignment; }
auto offset (const void *ptr) const
{
return m_successor.offset (ptr);
}
auto data (void) { return m_successor.data () - m_offset; }
auto data (void) const { return m_successor.data () - m_offset; }
auto begin (void) { return m_successor.begin () - m_offset; }
auto begin (void) const { return m_successor.begin () - m_offset; }
auto end (void) { return m_successor.end () - m_offset; }
auto end (void) const { return m_successor.end () - m_offset; }
auto reset (void) { return m_successor.reset (); }
auto capacity (void) const { return m_successor.capacity (); }
auto used (void) const { return m_successor.used (); }
auto remain (void) const { return m_successor.remain (); }
private:
direct<ChildT> m_successor;
std::ptrdiff_t m_offset;
std::size_t m_alignment;
};
}
#endif