102 lines
2.7 KiB
C++
102 lines
2.7 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2015 Danny Robson <danny@nerdcruft.net>
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*/
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#include "./stack.hpp"
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#include "../debug.hpp"
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#include "../pointer.hpp"
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using util::alloc::stack;
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///////////////////////////////////////////////////////////////////////////////
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stack::stack (void *begin, void *end):
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m_begin (reinterpret_cast<char*> (begin)),
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m_end (reinterpret_cast<char*> (end)),
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m_cursor (reinterpret_cast<char*> (begin))
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{
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CHECK_LE (m_begin, m_end);
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}
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///////////////////////////////////////////////////////////////////////////////
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union record {
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using offset_t = uint32_t;
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char *as_bytes;
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offset_t *as_uint32;
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};
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//-----------------------------------------------------------------------------
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constexpr auto MIN_ALIGNMENT = sizeof (record::offset_t);
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///////////////////////////////////////////////////////////////////////////////
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void*
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stack::allocate (size_t bytes, size_t alignment)
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{
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alignment = util::max (MIN_ALIGNMENT, alignment);
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// reserve space at the front of the allocation to record the total
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// allocation size so we can account for alignment if required.
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auto ptr = m_cursor + sizeof (record::offset_t);
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// align the outgoing pointer if required
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ptr = align (ptr, alignment);
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// ensure we haven't overrun our allocated segment
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if (ptr + bytes > m_end)
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throw std::bad_alloc ();
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// store the total size and record the new stack head
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record record;
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record.as_bytes = ptr - sizeof (record::offset_t);
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*record.as_uint32 = ptr - m_cursor;
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m_cursor = ptr + bytes;
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return ptr;
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}
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//-----------------------------------------------------------------------------
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void
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stack::deallocate (void *_ptr, size_t bytes, size_t alignment)
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{
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(void)bytes;
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alignment = util::max (MIN_ALIGNMENT, alignment);
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auto ptr = reinterpret_cast<char*> (_ptr);
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record record;
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record.as_bytes = ptr - sizeof (record::offset_t);
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CHECK_LE (bytes, *record.as_uint32);
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CHECK_GE (m_cursor - *record.as_uint32, m_begin);
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m_cursor -= *record.as_uint32 + bytes;
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}
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//-----------------------------------------------------------------------------
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void
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stack::reset (void)
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{
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m_cursor = m_begin;
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}
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