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btStackAlloc.h

/*
Copyright (c) 2003-2006 Gino van den Bergen / Erwin Coumans  http://continuousphysics.com/Bullet/

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.
*/

/*
StackAlloc extracted from GJK-EPA collision solver by Nathanael Presson
Nov.2006
*/

#ifndef BT_STACK_ALLOC
#define BT_STACK_ALLOC

#include "btScalar.h" //for btAssert
#include "btAlignedAllocator.h"

///The btBlock class is an internal structure for the btStackAlloc memory allocator.
00027 struct btBlock
{
      btBlock*                previous;
      unsigned char*          address;
};

///The StackAlloc class provides some fast stack-based memory allocator (LIFO last-in first-out)
00034 class btStackAlloc
{
public:

      btStackAlloc(unsigned int size)     { ctor();create(size); }
      ~btStackAlloc()         { destroy(); }
      
      inline void       create(unsigned int size)
      {
            destroy();
            data        =  (unsigned char*) btAlignedAlloc(size,16);
            totalsize   =     size;
      }
      inline void       destroy()
      {
            btAssert(usedsize==0);
            //Raise(L"StackAlloc is still in use");

            if(usedsize==0)
            {
                  if(!ischild && data)          
                        btAlignedFree(data);

                  data                    =     0;
                  usedsize                =     0;
            }
            
      }

      int   getAvailableMemory() const
      {
            return static_cast<int>(totalsize - usedsize);
      }

      unsigned char*                allocate(unsigned int size)
      {
            const unsigned int      nus(usedsize+size);
            if(nus<totalsize)
            {
                  usedsize=nus;
                  return(data+(usedsize-size));
            }
            btAssert(0);
            //&& (L"Not enough memory"));
            
            return(0);
      }
      SIMD_FORCE_INLINE btBlock*          beginBlock()
      {
            btBlock*    pb = (btBlock*)allocate(sizeof(btBlock));
            pb->previous      =     current;
            pb->address       =     data+usedsize;
            current                 =     pb;
            return(pb);
      }
      SIMD_FORCE_INLINE void        endBlock(btBlock* block)
      {
            btAssert(block==current);
            //Raise(L"Unmatched blocks");
            if(block==current)
            {
                  current           =     block->previous;
                  usedsize    =     (unsigned int)((block->address-data)-sizeof(btBlock));
            }
      }

private:
      void        ctor()
      {
            data        =     0;
            totalsize   =     0;
            usedsize    =     0;
            current           =     0;
            ischild           =     false;
      }
      unsigned char*          data;
      unsigned int            totalsize;
      unsigned int            usedsize;
      btBlock*    current;
      bool        ischild;
};

#endif //BT_STACK_ALLOC

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