libcruft-util/alloc/raw/stack.cpp

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/*
* 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 2015-2016 Danny Robson <danny@nerdcruft.net>
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*/
#include "stack.hpp"
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#include "../../debug.hpp"
#include "../../pointer.hpp"
#include "../../cast.hpp"
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using util::alloc::raw::stack;
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///////////////////////////////////////////////////////////////////////////////
stack::stack (void *begin, void *end):
m_begin (reinterpret_cast<std::byte*> (begin)),
m_end (reinterpret_cast<std::byte*> (end)),
m_cursor (m_begin)
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{
CHECK_LE (m_begin, m_end);
}
///////////////////////////////////////////////////////////////////////////////
union record {
using offset_t = uint32_t;
std::byte *as_bytes;
offset_t *as_offset;
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};
//-----------------------------------------------------------------------------
constexpr auto MIN_ALIGNMENT = sizeof (record::offset_t);
///////////////////////////////////////////////////////////////////////////////
void*
stack::allocate (size_t bytes)
{
return allocate (bytes, alignof (std::max_align_t));
}
//-----------------------------------------------------------------------------
void*
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stack::allocate (size_t bytes, size_t alignment)
{
// 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);
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ptr = 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.
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record record;
record.as_bytes = ptr - sizeof (record::offset_t);
*record.as_offset = util::cast::lossless <uint32_t> (ptr - m_cursor);
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m_cursor = ptr + bytes;
return ptr;
}
//-----------------------------------------------------------------------------
void
stack::deallocate (void *ptr, size_t bytes)
{
return deallocate (ptr, bytes, alignof (std::max_align_t));
}
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//-----------------------------------------------------------------------------
void
stack::deallocate (void *_ptr, size_t bytes, size_t alignment)
{
(void)bytes;
// TODO: use alignment
(void)alignment;
//alignment = util::max (MIN_ALIGNMENT, alignment);
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auto ptr = reinterpret_cast<std::byte*> (_ptr);
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record record;
record.as_bytes = ptr - sizeof (record::offset_t);
//CHECK_LE (bytes, *record.as_offset);
CHECK_GE (m_cursor - *record.as_offset, m_begin);
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m_cursor -= bytes;
m_cursor -= *record.as_offset;
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}
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//-----------------------------------------------------------------------------
std::byte*
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stack::begin (void)
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{
return m_begin;
}
//-----------------------------------------------------------------------------
const std::byte*
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stack::begin (void) const
{
return m_begin;
}
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//-----------------------------------------------------------------------------
size_t
stack::offset (const void *_ptr) const
{
auto ptr = reinterpret_cast<const std::byte*> (_ptr);
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CHECK_GE (ptr, m_begin);
return ptr - m_begin;
}
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//-----------------------------------------------------------------------------
void
stack::reset (void)
{
m_cursor = m_begin;
}
///////////////////////////////////////////////////////////////////////////////
size_t
stack::capacity (void) const
{
return m_end - m_begin;
}
//-----------------------------------------------------------------------------
size_t
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stack::used (void) const
{
return m_cursor - m_begin;
}
//-----------------------------------------------------------------------------
size_t
stack::remain (void) const
{
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return capacity () - used ();
}