/*******************************************************************************
 * fixedallocator.h
 *
 * Simple allocator using a fixed-size pool.
 *
 * Author: Christopher J. Cason.
 *
 * ---------------------------------------------------------------------------
 * Persistence of Vision Ray Tracer ('POV-Ray') version 3.7.
 * Copyright 1991-2013 Persistence of Vision Raytracer Pty. Ltd.
 *
 * POV-Ray is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * POV-Ray is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * ---------------------------------------------------------------------------
 * POV-Ray is based on the popular DKB raytracer version 2.12.
 * DKBTrace was originally written by David K. Buck.
 * DKBTrace Ver 2.0-2.12 were written by David K. Buck & Aaron A. Collins.
 * ---------------------------------------------------------------------------
 * $File: //depot/public/povray/3.x/source/backend/support/fixedallocator.h $
 * $Revision: #1 $
 * $Change: 6069 $
 * $DateTime: 2013/11/06 11:59:40 $
 * $Author: chrisc $
 *******************************************************************************/

#if !defined __FIXED_ALLOCATOR_H__
#define __FIXED_ALLOCATOR_H__

#include <cassert>

namespace pov
{
	template <typename T, int MaxElements>
	class FixedAllocator
	{
	public:
		typedef T               value_type ;
		typedef unsigned short  size_type ;
		typedef ptrdiff_t       difference_type;
		typedef T&              reference ;
		typedef const T&        const_reference ;
		typedef T               *pointer ;
		typedef const T         *const_pointer ;

	private:
		size_type byteCount (unsigned char nItems) { return ((size_type) nItems * sizeof (T)) ; }
		typedef struct
		{
			unsigned char nItems ;
			unsigned char allocated ;
		} BlockHeader ;

		void defrag (void)
		{
			unsigned char current = m_FirstFreeBlock ;
			while (current < MaxElements)
			{
				unsigned char next = current + m_Headers [current].nItems ;
				if (next >= MaxElements)
					break ;
				if (m_Headers [current].allocated || m_Headers [next].allocated)
				{
					current = next ;
					continue ;
				}
				m_Headers [current].nItems += m_Headers [next].nItems ;
				m_Headers [next].nItems = 0 ;
			}
		}

		unsigned char allocateBlocks (unsigned char nBlocks, unsigned char current)
		{
			assert (nBlocks > 0) ;
			while (current < MaxElements)
			{
				unsigned char next = current + m_Headers [current].nItems ;
				if (m_Headers [current].allocated == false && m_Headers [current].nItems >= nBlocks)
				{
					if (current + nBlocks < MaxElements && m_Headers [current].nItems > nBlocks)
					{
						m_Headers [current + nBlocks].nItems = m_Headers [current].nItems - nBlocks ;
						m_Headers [current + nBlocks].allocated = false ;
					}
					m_Headers [current].nItems = nBlocks ;
					m_Headers [current].allocated = true ;
					if (m_FirstFreeBlock == current)
						m_FirstFreeBlock = current + nBlocks ;
					return (current) ;
				}
				current = next ;
			}
			return (0xff) ;
		}

	public:
		// construct an allocator for the supplied new type.
		template <typename N>
		struct rebind { typedef FixedAllocator<N, MaxElements> other ; } ;

		size_type max_size() const { return (MaxElements) ; }
		pointer address (reference what) const { return (&what) ; }
		const_pointer address (const_reference what) const { return (&what) ; }
		FixedAllocator ()
		{
			if (MaxElements > 127)
				throw POV_EXCEPTION_CODE(kInternalLimitErr, "Internal limit exceeded in fixedallocator.h") ;
			m_FirstFreeBlock = 0 ;
			m_Headers [0].allocated = false ;
			m_Headers [0].nItems = MaxElements ;
		}
		~FixedAllocator () { }
		void construct (pointer where, T const& what) { new (where) T (what) ; }
		void destroy (pointer what) { what->~T() ; }

		pointer allocate (size_type nItems, std::allocator<void>::const_pointer hint = 0)
		{
			if (((unsigned char *) hint >= m_Data) && ((unsigned char *) hint < m_Data + sizeof (T) * MaxElements))
			{
				unsigned char slot = ((unsigned char *) hint - m_Data) / sizeof (T) ;
				if ((slot = allocateBlocks (nItems, slot)) != 0xff)
					return ((pointer) (m_Data + byteCount (slot))) ;
			}
			unsigned char slot = allocateBlocks (nItems, m_FirstFreeBlock) ;
			if (slot == 0xff)
			{
				defrag () ;
				if ((slot = allocateBlocks (nItems, m_FirstFreeBlock)) == 0xff)
					throw POV_EXCEPTION_CODE(kInternalLimitErr, "Internal limit exceeded in fixedallocator.h") ;
			}
			return ((pointer) (m_Data + byteCount (slot))) ;
		}

		void deallocate (pointer what, unsigned char nItems)
		{
			if (((unsigned char *) what >= m_Data) && ((unsigned char *) what < m_Data + sizeof (T) * MaxElements))
			{
				unsigned char slot = ((unsigned char *) what - m_Data) / sizeof (T) ;
				if (m_Headers [slot].allocated && m_Headers [slot].nItems == nItems)
				{
					m_Headers [slot].allocated = false ;
					if (m_FirstFreeBlock > slot)
					{
						m_FirstFreeBlock = slot ;
						assert (m_Headers [slot].nItems > 0) ;
					}
					unsigned char next = slot + nItems ;
					while (next < MaxElements && m_Headers [next].allocated == false)
					{
						m_Headers [slot].nItems += m_Headers [next].nItems ;
						m_Headers [next].nItems = 0 ;
						next = slot + m_Headers [slot].nItems ;
					}
				}
			}
		}

	private:
		unsigned char m_FirstFreeBlock ;
		unsigned char m_Data [sizeof (T) * MaxElements] ;
		BlockHeader m_Headers [MaxElements] ;
	} ;

	template <typename T>
	class MallocAllocator
	{
	public:
		typedef T               value_type ;
		typedef size_t          size_type ;
		typedef ptrdiff_t       difference_type;
		typedef T&              reference ;
		typedef const T&        const_reference ;
		typedef T               *pointer ;
		typedef const T         *const_pointer ;

	public:
		// construct an allocator for the supplied new type.
		template <typename N>
		struct rebind { typedef MallocAllocator<N> other ; } ;

		size_type max_size() const { return (0xffffffff) ; }
		pointer address (reference what) const { return (&what) ; }
		const_pointer address (const_reference what) const { return (&what) ; }
		MallocAllocator () { }
		~MallocAllocator () { }
		void construct (pointer where, T const& what) { new (where) T (what) ; }
		void destroy (pointer what) { what->~T() ; }

		pointer allocate (size_type nItems, std::allocator<void>::const_pointer hint = 0)
		{
			return ((pointer) malloc (sizeof (T) * nItems)) ;
		}

		void deallocate (pointer what, size_type nItems)
		{
			free (what) ;
		}
	} ;
} // end namespace pov

#endif