/*
  Copyright (C) 2018 David Robillard <d@drobilla.net>
  Copyright (C) 2006-2007 Chris Hamilton <chamilton@cs.dal.ca>

  This program is free software: you can redistribute it and/or modify it under
  the terms of the GNU General Public License as published by the Free Software
  Foundation, either version 2 of the License, or (at your option) any later
  version.

  This program 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 General Public License for more
  details.

  You should have received a copy of the GNU General Public License along with
  this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#ifndef CHILBERT_BITVECMASK_HPP
#define CHILBERT_BITVECMASK_HPP

#include <climits>
#include <cstddef>

namespace chilbert {
namespace detail {

/** Mask for a bit that can be incremented like an index.
 *
 * This enables fast iteration while setting or resetting bits since it is
 * internally stored as a mask which avoids repeated index math.
 */
template <class Rack>
struct BitVecMask
{
	static constexpr size_t bits_per_rack = sizeof(Rack) * CHAR_BIT;

	BitVecMask(const size_t index)
	  : rack{index / bits_per_rack}
	  , mask{Rack{1} << (index - rack * bits_per_rack)}
	{
	}

	void operator++()
	{
		if ((mask <<= 1) == 0) {
			mask = 1;
			++rack;
		}
	}

	void operator--()
	{
		if ((mask >>= 1) == 0) {
			mask = Rack{1} << (bits_per_rack - 1);
			--rack;
		}
	}

	bool operator==(const BitVecMask& rhs) const
	{
		return rack == rhs.rack && mask == rhs.mask;
	}

	bool operator!=(const BitVecMask& rhs) const { return !operator==(rhs); }

	size_t rack;
	Rack   mask;
};

} // namespace detail
} // namespace chilbert

#endif