b2BlockAllocator.cpp

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/*
* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#include <Box2D/Common/b2BlockAllocator.h>
#include <limits.h>
#include <string.h>
#include <stddef.h>

int32 b2BlockAllocator::s_blockSizes[b2_blockSizes] = 
{
        16,             // 0
        32,             // 1
        64,             // 2
        96,             // 3
        128,    // 4
        160,    // 5
        192,    // 6
        224,    // 7
        256,    // 8
        320,    // 9
        384,    // 10
        448,    // 11
        512,    // 12
        640,    // 13
};
uint8 b2BlockAllocator::s_blockSizeLookup[b2_maxBlockSize + 1];
bool b2BlockAllocator::s_blockSizeLookupInitialized;

struct b2Chunk
{
        int32 blockSize;
        b2Block* blocks;
};

struct b2Block
{
        b2Block* next;
};

b2BlockAllocator::b2BlockAllocator()
{
        b2Assert(b2_blockSizes < UCHAR_MAX);

        m_chunkSpace = b2_chunkArrayIncrement;
        m_chunkCount = 0;
        m_chunks = (b2Chunk*)b2Alloc(m_chunkSpace * sizeof(b2Chunk));
        
        memset(m_chunks, 0, m_chunkSpace * sizeof(b2Chunk));
        memset(m_freeLists, 0, sizeof(m_freeLists));

        if (s_blockSizeLookupInitialized == false)
        {
                int32 j = 0;
                for (int32 i = 1; i <= b2_maxBlockSize; ++i)
                {
                        b2Assert(j < b2_blockSizes);
                        if (i <= s_blockSizes[j])
                        {
                                s_blockSizeLookup[i] = (uint8)j;
                        }
                        else
                        {
                                ++j;
                                s_blockSizeLookup[i] = (uint8)j;
                        }
                }

                s_blockSizeLookupInitialized = true;
        }
}

b2BlockAllocator::~b2BlockAllocator()
{
        for (int32 i = 0; i < m_chunkCount; ++i)
        {
                b2Free(m_chunks[i].blocks);
        }

        b2Free(m_chunks);
}

void* b2BlockAllocator::Allocate(int32 size)
{
        if (size == 0)
                return NULL;

        b2Assert(0 < size);

        if (size > b2_maxBlockSize)
        {
                return b2Alloc(size);
        }

        int32 index = s_blockSizeLookup[size];
        b2Assert(0 <= index && index < b2_blockSizes);

        if (m_freeLists[index])
        {
                b2Block* block = m_freeLists[index];
                m_freeLists[index] = block->next;
                return block;
        }
        else
        {
                if (m_chunkCount == m_chunkSpace)
                {
                        b2Chunk* oldChunks = m_chunks;
                        m_chunkSpace += b2_chunkArrayIncrement;
                        m_chunks = (b2Chunk*)b2Alloc(m_chunkSpace * sizeof(b2Chunk));
                        memcpy(m_chunks, oldChunks, m_chunkCount * sizeof(b2Chunk));
                        memset(m_chunks + m_chunkCount, 0, b2_chunkArrayIncrement * sizeof(b2Chunk));
                        b2Free(oldChunks);
                }

                b2Chunk* chunk = m_chunks + m_chunkCount;
                chunk->blocks = (b2Block*)b2Alloc(b2_chunkSize);
#if defined(_DEBUG)
                memset(chunk->blocks, 0xcd, b2_chunkSize);
#endif
                int32 blockSize = s_blockSizes[index];
                chunk->blockSize = blockSize;
                int32 blockCount = b2_chunkSize / blockSize;
                b2Assert(blockCount * blockSize <= b2_chunkSize);
                for (int32 i = 0; i < blockCount - 1; ++i)
                {
                        b2Block* block = (b2Block*)((int8*)chunk->blocks + blockSize * i);
                        b2Block* next = (b2Block*)((int8*)chunk->blocks + blockSize * (i + 1));
                        block->next = next;
                }
                b2Block* last = (b2Block*)((int8*)chunk->blocks + blockSize * (blockCount - 1));
                last->next = NULL;

                m_freeLists[index] = chunk->blocks->next;
                ++m_chunkCount;

                return chunk->blocks;
        }
}

void b2BlockAllocator::Free(void* p, int32 size)
{
        if (size == 0)
        {
                return;
        }

        b2Assert(0 < size);

        if (size > b2_maxBlockSize)
        {
                b2Free(p);
                return;
        }

        int32 index = s_blockSizeLookup[size];
        b2Assert(0 <= index && index < b2_blockSizes);

#ifdef _DEBUG
        // Verify the memory address and size is valid.
        int32 blockSize = s_blockSizes[index];
        bool found = false;
        for (int32 i = 0; i < m_chunkCount; ++i)
        {
                b2Chunk* chunk = m_chunks + i;
                if (chunk->blockSize != blockSize)
                {
                        b2Assert(       (int8*)p + blockSize <= (int8*)chunk->blocks ||
                                                (int8*)chunk->blocks + b2_chunkSize <= (int8*)p);
                }
                else
                {
                        if ((int8*)chunk->blocks <= (int8*)p && (int8*)p + blockSize <= (int8*)chunk->blocks + b2_chunkSize)
                        {
                                found = true;
                        }
                }
        }

        b2Assert(found);

        memset(p, 0xfd, blockSize);
#endif

        b2Block* block = (b2Block*)p;
        block->next = m_freeLists[index];
        m_freeLists[index] = block;
}

void b2BlockAllocator::Clear()
{
        for (int32 i = 0; i < m_chunkCount; ++i)
        {
                b2Free(m_chunks[i].blocks);
        }

        m_chunkCount = 0;
        memset(m_chunks, 0, m_chunkSpace * sizeof(b2Chunk));

        memset(m_freeLists, 0, sizeof(m_freeLists));
}