fixedAllocator_inl.h

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// ============================================================================
#include <agrum/core/smallobjectallocator/fixedAllocator.h>
// ============================================================================

namespace gum {

  // ============================================================================
  // Initializes a Chunk object
  // ============================================================================
  INLINE void FixedAllocator::__Chunk::__init(const std::size_t&   blockSize,
                                              const unsigned char& numBlocks) {
    // Chunk memory space allocation. A chunk allocates a memory of blockSize *
    // numBlocks size.
    // The chunk will then give us numBlocks distinct blocks of blockSize from
    // that space.
    __pData = new unsigned char[blockSize * numBlocks];

    // The first available block of memory is logically at the beginning.
    __firstAvailableBlock = 0;

    // The number of block still available is all the blocks at the beginning.
    __blocksAvailable = numBlocks;

    // For each unallocated block, the first byte contains a number.
    // That number is the index of the next available block
    // Since we're at the beginning, next free block is the next one simply.
    // Following code initiate those number for each block
    unsigned char* p = __pData;
    for (unsigned char indexBlock = 0; indexBlock != numBlocks; p += blockSize)
      *p = ++indexBlock;
  }

  // ============================================================================
  // Allocates a block of memory
  // ============================================================================
  INLINE void* FixedAllocator::__Chunk::__allocate(const std::size_t& blockSize) {
    if (!__blocksAvailable)
      // If no block is available return nullptr
      return NULL;

    // __pData points to the beginning of allocated space.
    // __firstAvailableBlock gives us how many block to pass before getting
    // the good one. We have to multiply by blockSize to get the good memory
    // emplacement
    unsigned char* pResult = __pData + (__firstAvailableBlock * blockSize);

    // Remember that the first byte of each block gives us the index of next
    // available slot.
    // The new first availble block will be at the index indicating in this
    // block.
    __firstAvailableBlock = *pResult;

    // We lose one block
    --__blocksAvailable;

    return pResult;
  }

  // ============================================================================
  // Deallocates a block of memory
  // ============================================================================
  INLINE void FixedAllocator::__Chunk::__deallocat(void* pDeallocatedBlock,
                                                   const std::size_t& blockSize) {
    // first, ensure that deallocated is in this chunk
    GUM_ASSERT(pDeallocatedBlock >= __pData);

    // Conversion pf pointer for handling
    unsigned char* toRelease = static_cast< unsigned char* >(pDeallocatedBlock);

    // Alignement check
    GUM_ASSERT((toRelease - __pData) % blockSize == 0);

    // First byte of toRelease has now to give the index of current first
    // available block
    *toRelease = __firstAvailableBlock;

    // So that first available block points to it
    __firstAvailableBlock =
       static_cast< unsigned char >((toRelease - __pData) / blockSize);

    // Truncation check
    GUM_ASSERT(__firstAvailableBlock == (toRelease - __pData) / blockSize);

    // We gain one block, yeah
    ++__blocksAvailable;
  }

  // ============================================================================
  // Releases the allocated memory
  // ============================================================================
  INLINE void FixedAllocator::__Chunk::__release() { delete[] __pData; }


  // ############################################################################
  // @name Constructors / Destructors
  // ############################################################################

  // ============================================================================
  // Constructor.
  // ============================================================================
  INLINE FixedAllocator::FixedAllocator(const std::size_t&   blockSize,
                                        const unsigned char& numBlocks) {
    //    GUM_CONSTRUCTOR(FixedAllocator)
    __blockSize = blockSize;
    __numBlocks = numBlocks;
    __allocChunk = __chunks.begin();
    __deallocChunk = __chunks.begin();
  }

  // ============================================================================
  // Destructor.
  // ============================================================================
  INLINE FixedAllocator::~FixedAllocator() {
    for (__Chunks::iterator chunkIter = __chunks.begin();
         chunkIter != __chunks.end();
         ++chunkIter)
      chunkIter->__release();
    //    GUM_DESTRUCTOR(FixedAllocator)
  }

  // ############################################################################
  // @name Allocator / Deallocator
  // ############################################################################

  // ============================================================================
  // Allocates a block
  // ============================================================================
  INLINE void* FixedAllocator::allocate() {
    if (__chunks.empty() || __allocChunk->__blocksAvailable == 0) {
      // no available memory in this chunk
      // Try to find one with memory available
      for (__Chunks::iterator chunksIter = __chunks.begin();; ++chunksIter) {
        if (chunksIter == __chunks.end()) {
          // All chunks are filled up. Adding a new one
          __chunks.reserve(__chunks.size() + 1);
          __Chunk newChunk;
          newChunk.__init(__blockSize, __numBlocks);
          __chunks.push_back(newChunk);
          __allocChunk = __chunks.end();
          --__allocChunk;
          __deallocChunk = __allocChunk;
          break;
        }
        if (chunksIter->__blocksAvailable > 0) {
          // Found a chunk
          __allocChunk = chunksIter;
          break;
        }
      }
    }
    return __allocChunk->__allocate(__blockSize);
  }

  // ============================================================================
  // Deallocates a block
  // ============================================================================
  INLINE void FixedAllocator::deallocate(void* pDeallocatedBlock) {
    if (__deallocChunk->__pData > pDeallocatedBlock
        || pDeallocatedBlock
              > (__deallocChunk->__pData + (__numBlocks * __blockSize))) {
      // If not things get ugly
      // We have to find where the Chunk containing this pointer is
      std::ptrdiff_t offset = 0;

      // We perform a bidirectionnal search from __deallocChunk
      while (true) {
        ++offset;
        // First we look for the one going to the end of the vector
        if ((__deallocChunk + offset) < __chunks.end()) {
          if ((__deallocChunk + offset)->__pData <= pDeallocatedBlock
              && pDeallocatedBlock < ((__deallocChunk + offset)->__pData
                                      + (__numBlocks * __blockSize))) {
            // If pointed chunk contains this pointer, deallocation find the
            // place
            __deallocChunk = (__deallocChunk + offset);
            break;
          }
        }

        // Then we look for the one going to the beginning of the vector
        if ((__deallocChunk - offset) >= __chunks.begin()) {
          if ((__deallocChunk - offset)->__pData <= pDeallocatedBlock
              && pDeallocatedBlock < ((__deallocChunk - offset)->__pData
                                      + (__numBlocks * __blockSize))) {
            // If pointed chunk contains this pointer, deallocation find the
            // place
            __deallocChunk = (__deallocChunk - offset);
            break;
          }
        }
      }
    }
    __deallocChunk->__deallocat(pDeallocatedBlock, __blockSize);
  }

}   // namespace gum