boost::gil::memunit_distance

template<typename NonAlignedPixelReference>
std::ptrdiff_t
memunit_distance(
    bit_aligned_pixel_iterator<NonAlignedPixelReference> const& p1,
    bit_aligned_pixel_iterator<NonAlignedPixelReference> const& p2);

template<typename Iterator>
std::ptrdiff_t
memunit_distance(
    memory_based_step_iterator<Iterator> const& p1,
    memory_based_step_iterator<Iterator> const& p2);

template<typename P>
std::ptrdiff_t
memunit_distance(
    P const* p1,
    P const* p2);

template<
    typename Iterator,
    typename DFn>
std::iterator_traits<Iterator>::difference_type
memunit_distance(
    dereference_iterator_adaptor<Iterator, DFn> const& p1,
    dereference_iterator_adaptor<Iterator, DFn> const& p2);

template<
    typename IC,
    typename C>
std::ptrdiff_t
memunit_distance(
    planar_pixel_iterator<IC, C> const& p1,
    planar_pixel_iterator<IC, C> const& p2);