// Copyright 2018-2022 David Robillard <d@drobilla.net>
// Copyright 2006-2007 Chris Hamilton <chamilton@cs.dal.ca>
// SPDX-License-Identifier: GPL-2.0-or-later

#ifndef CHILBERT_DETAIL_BITVECMASK_HPP
#define CHILBERT_DETAIL_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;

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

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

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