allocator.h

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 * Software License Agreement (BSD License)
 *
 * Copyright 2008-2009  Marius Muja (mariusm@cs.ubc.ca). All rights reserved.
 * Copyright 2008-2009  David G. Lowe (lowe@cs.ubc.ca). All rights reserved.
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 * THE BSD LICENSE
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#ifndef FLANN_ALLOCATOR_H_
#define FLANN_ALLOCATOR_H_
 
#include <stdlib.h>
#include <stdio.h>
 
 
namespace flann
{
 
template <typename T>
T* allocate(size_t count = 1)
{
    T* mem = (T*) ::malloc(sizeof(T)*count);
    return mem;
}
 
 
 
const size_t     WORDSIZE=16;
const  size_t     BLOCKSIZE=8192;
 
class PooledAllocator
{
    /* We maintain memory alignment to word boundaries by requiring that all
        allocations be in multiples of the machine wordsize.  */
    /* Size of machine word in bytes.  Must be power of 2. */
    /* Minimum number of bytes requested at a time from the system.  Must be multiple of WORDSIZE. */
 
 
    int     remaining;  /* Number of bytes left in current block of storage. */
    void*   base;     /* Pointer to base of current block of storage. */
    void*   loc;      /* Current location in block to next allocate memory. */
    int     blocksize;
 
 
public:
    int     usedMemory;
    int     wastedMemory;
 
    PooledAllocator(int blocksize = BLOCKSIZE)
    {
        this->blocksize = blocksize;
        remaining = 0;
        base = NULL;
 
        usedMemory = 0;
        wastedMemory = 0;
    }
 
    ~PooledAllocator()
    {
        free();
    }
    
    void free()
    {
        void* prev;
        while (base != NULL) {
            prev = *((void**) base); /* Get pointer to prev block. */
            ::free(base);
            base = prev;
        }
        base = NULL;
        remaining = 0;
        usedMemory = 0;
        wastedMemory = 0;
    }
 
    void* allocateMemory(int size)
    {
        int blocksize;
 
        /* Round size up to a multiple of wordsize.  The following expression
            only works for WORDSIZE that is a power of 2, by masking last bits of
            incremented size to zero.
         */
        size = (size + (WORDSIZE - 1)) & ~(WORDSIZE - 1);
 
        /* Check whether a new block must be allocated.  Note that the first word
            of a block is reserved for a pointer to the previous block.
         */
        if (size > remaining) {
 
            wastedMemory += remaining;
 
            /* Allocate new storage. */
            blocksize = (size + sizeof(void*) + (WORDSIZE-1) > BLOCKSIZE) ?
                        size + sizeof(void*) + (WORDSIZE-1) : BLOCKSIZE;
 
            // use the standard C malloc to allocate memory
            void* m = ::malloc(blocksize);
            if (!m) {
                fprintf(stderr,"Failed to allocate memory.\n");
                return NULL;
            }
 
            /* Fill first word of new block with pointer to previous block. */
            ((void**) m)[0] = base;
            base = m;
 
            int shift = 0;
            //int shift = (WORDSIZE - ( (((size_t)m) + sizeof(void*)) & (WORDSIZE-1))) & (WORDSIZE-1);
 
            remaining = blocksize - sizeof(void*) - shift;
            loc = ((char*)m + sizeof(void*) + shift);
        }
        void* rloc = loc;
        loc = (char*)loc + size;
        remaining -= size;
 
        usedMemory += size;
 
        return rloc;
    }
 
    template <typename T>
    T* allocate(size_t count = 1)
    {
        T* mem = (T*) this->allocateMemory((int)(sizeof(T)*count));
        return mem;
    }
 
};
 
}
 
inline void* operator new (std::size_t size, flann::PooledAllocator& allocator)
{
    return allocator.allocateMemory(size) ;
}
 
#endif //FLANN_ALLOCATOR_H_