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fix_alloc.cpp

См. документацию.

/*
 * Copyright (C) Sergey P. Derevyago, 2003-2004.
 *
 * Permission to copy, use, modify, sell and distribute this software is granted
 * provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied warranty, and
 * with no claim as to its suitability for any purpose.
 *
 */

#include "fix_alloc.hpp"

namespace {

 const size_t CHUNK_SIZE=4*1024;

 const size_t SVP=sizeof(void*);

 const size_t MAX_SIZE=128;

 const size_t HEADS_NUM=(MAX_SIZE+SVP-1)/SVP;

 void* heads[HEADS_NUM];

}

void fixed_alloc_private::get_mem(void*& head, size_t type_sz)
{
 size_t n=(CHUNK_SIZE>type_sz) ? CHUNK_SIZE/type_sz : 1;
 head=operator new(n*type_sz);

 char* last=(char*)head+(n-1)*type_sz;
 for (char* ptr=(char*)head; ; ptr+=type_sz) {
     if (ptr!=last) *(void**)ptr=ptr+type_sz;
     else {
          *(void**)ptr=0;
          break;
     }
 }
}

void* sized_alloc::alloc(size_t size)
{
 size_t index=(size+SVP-1)/SVP;
 if (index>=HEADS_NUM) return operator new(size);

 void*& head=heads[index];
 if (!head) fixed_alloc_private::get_mem(head, index*SVP);

 void* ret=head;
 head=*(void**)head;

 return ret;
}

void sized_alloc::free(void* ptr, size_t size)
{
 size_t index=(size+SVP-1)/SVP;
 if (index>=HEADS_NUM) operator delete(ptr);
 else {
      void*& head=heads[index];

      *(void**)ptr=head;
      head=ptr;
 }
}

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