Function advance

3rd/asio-1.24.0/include/asio/buffers_iterator.hpp:407–485

Advance the iterator by the specified distance.

  // Advance the iterator by the specified distance.
  void advance(std::ptrdiff_t n)
  {
    if (n > 0)
    {
      ASIO_ASSERT(current_ != end_ && "iterator out of bounds");
      for (;;)
      {
        std::ptrdiff_t current_buffer_balance
          = current_buffer_.size() - current_buffer_position_;

        // Check if the advance can be satisfied by the current buffer.
        if (current_buffer_balance > n)
        {
          position_ += n;
          current_buffer_position_ += n;
          return;
        }

        // Update position.
        n -= current_buffer_balance;
        position_ += current_buffer_balance;

        // Move to next buffer. If it is empty then it will be skipped on the
        // next iteration of this loop.
        if (++current_ == end_)
        {
          ASIO_ASSERT(n == 0 && "iterator out of bounds");
          current_buffer_ = buffer_type();
          current_buffer_position_ = 0;
          return;
        }
        current_buffer_ = *current_;
        current_buffer_position_ = 0;
      }
    }
    else if (n < 0)
    {
      std::size_t abs_n = -n;
      ASIO_ASSERT(position_ >= abs_n && "iterator out of bounds");
      for (;;)
      {
        // Check if the advance can be satisfied by the current buffer.
        if (current_buffer_position_ >= abs_n)
        {
          position_ -= abs_n;
          current_buffer_position_ -= abs_n;
          return;
        }

        // Update position.
        abs_n -= current_buffer_position_;
        position_ -= current_buffer_position_;

        // Check if we've reached the beginning of the buffers.
        if (current_ == begin_)
        {
          ASIO_ASSERT(abs_n == 0 && "iterator out of bounds");
          current_buffer_position_ = 0;