libcruft-util/alloc/raw/stack.hpp

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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
* Copyright 2015 Danny Robson <danny@nerdcruft.net>
*/
#ifndef CRUFT_UTIL_ALLOC_RAW_STACK_HPP
#define CRUFT_UTIL_ALLOC_RAW_STACK_HPP
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#include "../../view.hpp"
#include "../../pointer.hpp"
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#include <cstddef>
namespace util::alloc::raw {
// allocate memory from a buffer in a stacklike manner. deallocation that
// is not correctly ordered has undefined (read 'bad') results.
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class stack {
public:
stack (const stack&) = delete;
stack (stack&&) = delete;
stack& operator= (const stack&) = delete;
stack& operator= (stack&&) = delete;
stack (util::view<std::byte*> _data);
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template <typename T>
util::view<T*>
allocate (size_t count, size_t alignment)
{
constexpr auto MIN_ALIGNMENT = sizeof (record::offset_t);
const auto bytes = count * sizeof (T);
// reserve space at the front of the allocation to record the total
// allocation size so we can account for alignment if required.
auto ptr = m_cursor + sizeof (record::offset_t);
// align the outgoing pointer if required
alignment = util::max (MIN_ALIGNMENT, alignment);
ptr = util::align (ptr, alignment);
// ensure we haven't overrun our allocated segment
if (ptr + bytes > m_end)
throw std::bad_alloc ();
// use a 'record' struct as a window into the reserved space at the front
// of the allocation and store the offset to the previous allocation head
// (from the record struct). allows us to account for alignment.
record r;
r.as_bytes = ptr - sizeof (record::offset_t);
*r.as_offset = util::cast::lossless <uint32_t> (ptr - m_cursor);
m_cursor = ptr + bytes;
return { util::cast::alignment<T*> (ptr), count };
}
template <typename T>
util::view<T*>
allocate (size_t count)
{
return allocate<T> (count, alignof (T));
}
template <typename T>
void deallocate (util::view<T*> _ptr)
{
auto ptr = reinterpret_cast<std::byte*> (_ptr.data ());
record r;
r.as_bytes = ptr - sizeof (record::offset_t);
//CHECK_LE (bytes, *record.as_offset);
CHECK_GE (m_cursor - *r.as_offset, m_begin);
m_cursor -= sizeof (T) * _ptr.size ();
m_cursor -= *r.as_offset;
}
util::view<std::byte*> data (void);
util::view<const std::byte*> data (void) const;
std::byte* begin (void);
const std::byte* begin (void) const;
std::byte* end (void);
const std::byte* end (void) const;
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size_t offset (const void*) const;
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void reset (void);
size_t capacity (void) const;
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size_t used (void) const;
size_t remain (void) const;
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private:
union record {
using offset_t = uint32_t;
std::byte *as_bytes;
offset_t *as_offset;
};
std::byte *const m_begin;
std::byte *const m_end;
std::byte *m_cursor;
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};
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}
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#endif