libcruft-util/alloc/stack.cpp

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2015-11-13 17:17:37 +11:00
/*
* 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 Danny Robson <danny@nerdcruft.net>
*/
#include "./stack.hpp"
#include "../debug.hpp"
#include "../pointer.hpp"
using util::alloc::stack;
///////////////////////////////////////////////////////////////////////////////
stack::stack (void *begin, void *end):
m_begin (reinterpret_cast<char*> (begin)),
m_end (reinterpret_cast<char*> (end)),
m_cursor (reinterpret_cast<char*> (begin))
{
CHECK_LE (m_begin, m_end);
}
///////////////////////////////////////////////////////////////////////////////
union record {
using offset_t = uint32_t;
char *as_bytes;
offset_t *as_uint32;
};
//-----------------------------------------------------------------------------
constexpr auto MIN_ALIGNMENT = sizeof (record::offset_t);
///////////////////////////////////////////////////////////////////////////////
void*
stack::allocate (size_t bytes, size_t alignment)
{
alignment = util::max (MIN_ALIGNMENT, 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
ptr = align (ptr, alignment);
// ensure we haven't overrun our allocated segment
if (ptr + bytes > m_end)
throw std::bad_alloc ();
// store the total size and record the new stack head
record record;
record.as_bytes = ptr - sizeof (record::offset_t);
*record.as_uint32 = ptr - m_cursor;
m_cursor = ptr + bytes;
return ptr;
}
//-----------------------------------------------------------------------------
void
stack::deallocate (void *_ptr, size_t bytes, size_t alignment)
{
(void)bytes;
alignment = util::max (MIN_ALIGNMENT, alignment);
auto ptr = reinterpret_cast<char*> (_ptr);
record record;
record.as_bytes = ptr - sizeof (record::offset_t);
CHECK_LE (bytes, *record.as_uint32);
CHECK_GE (m_cursor - *record.as_uint32, m_begin);
m_cursor -= *record.as_uint32 + bytes;
}
//-----------------------------------------------------------------------------
void
stack::reset (void)
{
m_cursor = m_begin;
}