genode/base/include/util/bit_allocator.h

/*
 * \brief  Allocator using bitmaps
 * \author Alexander Boettcher
 * \author Stefan Kalkowski
 * \date   2012-06-14
 */

/*
 * Copyright (C) 2012-2013 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _INCLUDE__UTIL__BIT_ALLOCATOR_H_
#define _INCLUDE__UTIL__BIT_ALLOCATOR_H_

#include <util/bit_array.h>

namespace Genode {

	template<unsigned BITS>
	class Bit_allocator
	{
		protected:

			addr_t          _next;
			Bit_array<BITS> _array;

			void _reserve(addr_t bit_start, size_t const num)
			{
				if (!num) return;

				_array.set(bit_start, num);
			}

		public:

			class Out_of_indices : Exception {};

			Bit_allocator() : _next(0) { }

			addr_t alloc(size_t const num_log2 = 0)
			{
				addr_t const step = 1UL << num_log2;
				addr_t max = ~0UL;

				do {
					try {
						/* throws exception if array is accessed outside bounds */
						for (addr_t i = _next & ~(step - 1); i < max; i += step) {
							if (_array.get(i, step))
								continue;

							_array.set(i, step);
							_next = i + step;
							return i;
						}
					} catch (typename Bit_array<BITS>::Invalid_index_access) { }

					max = _next;
					_next = 0;

				} while (max != 0);

				throw Out_of_indices();
			}

			void free(addr_t const bit_start, size_t const num_log2 = 0)
			{
				_array.clear(bit_start, 1UL << num_log2);
				_next = bit_start;
			}
	};
}
#endif /* _INCLUDE__UTIL__BIT_ALLOCATOR_H_ */