find_next.c

static void init_range(uint64_t *bitmap, size_t bitmap_size,
                       size_t size_required,
                       struct range_finder *restrict range) {
  range->bitmap = bitmap;
  range->bitmap_size = bitmap_size;
  range->size_required = size_required;
  range->current = bitmap[0];
  range->previous_set_bit = ULONG_MAX;
  range->index = 0;
}

static bool find_next(struct range_finder *restrict range) {
  do {
    if (find_range_once(range)) {
      if (range->current_set_bit % 64) {
        // mask the already found item
        uint64_t mask = ~(ULONG_MAX << (range->current_set_bit % 64));
        range->current |= mask;
      } else {
        // run out in the current word, but maybe we
        // have more in the next?
        if (range->index + 1 < range->bitmap_size) {
          range->index++;
          range->current = range->bitmap[range->index];
          continue;
        } else {
          range->current = ULONG_MAX;
        }
      }
      return true;
    }
    range->index++;
    if (range->index >= range->bitmap_size)
      return false;
    range->current = range->bitmap[range->index];
  } while (true);
}