Boost C++ Libraries

boost/gil/channel.hpp

//
// Copyright 2005-2007 Adobe Systems Incorporated
//
// Distributed under the Boost Software License, Version 1.0
// See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt
//
#ifndef BOOST_GIL_CHANNEL_HPP
#define BOOST_GIL_CHANNEL_HPP

#include <boost/gil/utilities.hpp>

#include <boost/config.hpp>
#include <boost/config/pragma_message.hpp>
#include <boost/integer/integer_mask.hpp>
#include <boost/type_traits/remove_cv.hpp>

#include <cassert>
#include <cstdint>
#include <limits>

#ifdef BOOST_GIL_DOXYGEN_ONLY
/// \def BOOST_GIL_CONFIG_HAS_UNALIGNED_ACCESS
/// \brief Define to allow unaligned memory access for models of packed channel value.
/// Theoretically (or historically?) on platforms which support dereferencing on
/// non-word memory boundary, unaligned access may result in performance improvement.
/// \warning Unfortunately, this optimization may be a C/C++ strict aliasing rules
/// violation, if accessed data buffer has effective type that cannot be aliased
/// without leading to undefined behaviour.
#define BOOST_GIL_CONFIG_HAS_UNALIGNED_ACCESS
#endif

#ifdef BOOST_GIL_CONFIG_HAS_UNALIGNED_ACCESS
#if defined(sun) || defined(__sun) || \             // SunOS
    defined(__osf__) || defined(__osf) || \         // Tru64
    defined(_hpux) || defined(hpux) || \            // HP-UX
    defined(__arm__) || defined(__ARM_ARCH) || \    // ARM
    defined(_AIX)                                   // AIX
#error Unaligned access strictly disabled for some UNIX platforms or ARM architecture
#elif defined(__i386__) || defined(__x86_64__) || defined(__vax__)
    // The check for little-endian architectures that tolerate unaligned memory
    // accesses is just an optimization. Nothing will break if it fails to detect
    // a suitable architecture.
    //
    // Unfortunately, this optimization may be a C/C++ strict aliasing rules violation
    // if accessed data buffer has effective type that cannot be aliased
    // without leading to undefined behaviour.
BOOST_PRAGMA_MESSAGE("CAUTION: Unaligned access tolerated on little-endian may cause undefined behaviour")
#else
#error Unaligned access disabled for unknown platforms and architectures
#endif
#endif // defined(BOOST_GIL_CONFIG_HAS_UNALIGNED_ACCESS)

namespace boost { namespace gil {

///////////////////////////////////////////
////  channel_traits
////
////  \ingroup ChannelModel
////  \class channel_traits
////  \brief defines properties of channels, such as their range and associated types
////
////  The channel traits must be defined for every model of ChannelConcept
////  Default traits are provided. For built-in types the default traits use
////  built-in pointer and reference and the channel range is the physical
////  range of the type. For classes, the default traits forward the associated types
////  and range to the class.
////
///////////////////////////////////////////

namespace detail {
    template <typename T, bool is_class> struct channel_traits_impl;

    // channel traits for custom class
    template <typename T>
    struct channel_traits_impl<T, true> {
        typedef typename T::value_type      value_type;
        typedef typename T::reference       reference;
        typedef typename T::pointer         pointer;
        typedef typename T::const_reference const_reference;
        typedef typename T::const_pointer   const_pointer;
        BOOST_STATIC_CONSTANT(bool, is_mutable=T::is_mutable);
        static value_type min_value() { return T::min_value(); }
        static value_type max_value() { return T::max_value(); }
    };

    // channel traits implementation for built-in integral or floating point channel type
    template <typename T>
    struct channel_traits_impl<T, false> {
        typedef T           value_type;
        typedef T&          reference;
        typedef T*          pointer;
        typedef const T&    const_reference;
        typedef T const*    const_pointer;
        BOOST_STATIC_CONSTANT(bool, is_mutable=true);
        static value_type min_value() { return (std::numeric_limits<T>::min)(); }
        static value_type max_value() { return (std::numeric_limits<T>::max)(); }
    };

    // channel traits implementation for constant built-in scalar or floating point type
    template <typename T>
    struct channel_traits_impl<const T, false> : public channel_traits_impl<T, false> {
        typedef const T&    reference;
        typedef const T*    pointer;
        BOOST_STATIC_CONSTANT(bool, is_mutable=false);
    };
}

/**
\ingroup ChannelModel
\brief Traits for channels. Contains the following members:
\code
template <typename Channel>
struct channel_traits {
    typedef ... value_type;
    typedef ... reference;
    typedef ... pointer;
    typedef ... const_reference;
    typedef ... const_pointer;

    static const bool is_mutable;
    static value_type min_value();
    static value_type max_value();
};
\endcode
*/
template <typename T>
struct channel_traits : public detail::channel_traits_impl<T, is_class<T>::value> {};

// Channel traits for C++ reference type - remove the reference
template <typename T> struct channel_traits<      T&> : public channel_traits<T> {};

// Channel traits for constant C++ reference type
template <typename T> struct channel_traits<const T&> : public channel_traits<T> {
    typedef typename channel_traits<T>::const_reference reference;
    typedef typename channel_traits<T>::const_pointer   pointer;
    BOOST_STATIC_CONSTANT(bool, is_mutable=false);
};

///////////////////////////////////////////
////
////  scoped_channel_value
////
///////////////////////////////////////////

/**
\defgroup ScopedChannelValue scoped_channel_value
\ingroup ChannelModel
\brief A channel adaptor that modifies the range of the source channel. Models: ChannelValueConcept

Example:
\code
// Create a double channel with range [-0.5 .. 0.5]
struct double_minus_half  { static double apply() { return -0.5; } };
struct double_plus_half   { static double apply() { return  0.5; } };
typedef scoped_channel_value<double, double_minus_half, double_plus_half> bits64custom_t;

// channel_convert its maximum should map to the maximum
bits64custom_t x = channel_traits<bits64custom_t>::max_value();
assert(x == 0.5);
uint16_t y = channel_convert<uint16_t>(x);
assert(y == 65535);
\endcode
*/

/// \ingroup ScopedChannelValue
/// \brief A channel adaptor that modifies the range of the source channel. Models: ChannelValueConcept
template <typename BaseChannelValue,        // base channel (models ChannelValueConcept)
          typename MinVal, typename MaxVal> // classes with a static apply() function returning the minimum/maximum channel values
struct scoped_channel_value {
    typedef scoped_channel_value    value_type;
    typedef value_type&             reference;
    typedef value_type*             pointer;
    typedef const value_type&       const_reference;
    typedef const value_type*       const_pointer;
    BOOST_STATIC_CONSTANT(bool, is_mutable=channel_traits<BaseChannelValue>::is_mutable);

    typedef BaseChannelValue base_channel_t;

    static value_type min_value() { return MinVal::apply(); }
    static value_type max_value() { return MaxVal::apply(); }

    scoped_channel_value() {}
    scoped_channel_value(const scoped_channel_value& c) : _value(c._value) {}
    scoped_channel_value(BaseChannelValue val) : _value(val) {}

    scoped_channel_value& operator++() { ++_value; return *this; }
    scoped_channel_value& operator--() { --_value; return *this; }

    scoped_channel_value operator++(int) { scoped_channel_value tmp=*this; this->operator++(); return tmp; }
    scoped_channel_value operator--(int) { scoped_channel_value tmp=*this; this->operator--(); return tmp; }

    template <typename Scalar2> scoped_channel_value& operator+=(Scalar2 v) { _value+=v; return *this; }
    template <typename Scalar2> scoped_channel_value& operator-=(Scalar2 v) { _value-=v; return *this; }
    template <typename Scalar2> scoped_channel_value& operator*=(Scalar2 v) { _value*=v; return *this; }
    template <typename Scalar2> scoped_channel_value& operator/=(Scalar2 v) { _value/=v; return *this; }

    scoped_channel_value& operator=(BaseChannelValue v) { _value=v; return *this; }
    operator BaseChannelValue() const { return _value; }
private:
    BaseChannelValue _value;
};

template <typename T>
struct float_point_zero
{
    static constexpr T apply() { return 0.0f; }
};

template <typename T>
struct float_point_one
{
    static constexpr T apply() { return 1.0f; }
};

///////////////////////////////////////////
////
////  Support for sub-byte channels. These are integral channels whose value is contained in a range of bits inside an integral type
////
///////////////////////////////////////////

// It is necessary for packed channels to have their own value type. They cannot simply use an integral large enough to store the data. Here is why:
// - Any operation that requires returning the result by value will otherwise return the built-in integral type, which will have incorrect range
//   That means that after getting the value of the channel we cannot properly do channel_convert, channel_invert, etc.
// - Two channels are declared compatible if they have the same value type. That means that a packed channel is incorrectly declared compatible with an integral type
namespace detail {
    // returns the smallest fast unsigned integral type that has at least NumBits bits
    template <int NumBits>
    struct min_fast_uint : public mpl::if_c< (NumBits<=8),
            uint_least8_t,
            typename mpl::if_c< (NumBits<=16),
                    uint_least16_t,
                    typename mpl::if_c< (NumBits<=32),
                            uint_least32_t,
                            uintmax_t
                    >::type
            >::type
          > {};

    template <int NumBits>
    struct num_value_fn : public mpl::if_c< ( NumBits < 32 )
                                          , uint32_t
                                          , uint64_t
                                          > {};

    template <int NumBits>
    struct max_value_fn : public mpl::if_c< ( NumBits <= 32 )
                                          , uint32_t
                                          , uint64_t
                                          > {};
}

/**
\defgroup PackedChannelValueModel packed_channel_value
\ingroup ChannelModel
\brief Represents the value of an unsigned integral channel operating over a bit range. Models: ChannelValueConcept
Example:
\code
// A 4-bit unsigned integral channel.
typedef packed_channel_value<4> bits4;

assert(channel_traits<bits4>::min_value()==0);
assert(channel_traits<bits4>::max_value()==15);
assert(sizeof(bits4)==1);
BOOST_STATIC_ASSERT((boost::is_integral<bits4>::value));
\endcode
*/

/// \ingroup PackedChannelValueModel
/// \brief The value of a subbyte channel. Models: ChannelValueConcept
template <int NumBits>
class packed_channel_value {

public:
    typedef typename detail::min_fast_uint<NumBits>::type integer_t;


    typedef packed_channel_value   value_type;
    typedef value_type&            reference;
    typedef const value_type&      const_reference;
    typedef value_type*            pointer;
    typedef const value_type*      const_pointer;

    static value_type min_value() { return 0; }
    static value_type max_value() { return low_bits_mask_t< NumBits >::sig_bits; }

    BOOST_STATIC_CONSTANT(bool, is_mutable=true);

    packed_channel_value() {}

    packed_channel_value(integer_t v) { _value = static_cast< integer_t >( v & low_bits_mask_t<NumBits>::sig_bits_fast ); }
    template <typename Scalar> packed_channel_value(Scalar v) { _value = packed_channel_value( static_cast< integer_t >( v ) ); }

    static unsigned int num_bits() { return NumBits; }

    operator integer_t() const { return _value; }
private:
    integer_t _value;
};

namespace detail {

template <std::size_t K>
struct static_copy_bytes {
    void operator()(const unsigned char* from, unsigned char* to) const {
        *to = *from;
        static_copy_bytes<K-1>()(++from,++to);
    }
};

template <>
struct static_copy_bytes<0> {
    void operator()(const unsigned char* , unsigned char*) const {}
};

template <typename Derived, typename BitField, int NumBits, bool Mutable>
class packed_channel_reference_base {
protected:
    typedef typename mpl::if_c<Mutable,void*,const void*>::type data_ptr_t;
public:
    data_ptr_t _data_ptr;   // void* pointer to the first byte of the bit range

    typedef packed_channel_value<NumBits>   value_type;
    typedef const Derived                   reference;
    typedef value_type*                     pointer;
    typedef const value_type*               const_pointer;
    BOOST_STATIC_CONSTANT(int,  num_bits=NumBits);
    BOOST_STATIC_CONSTANT(bool, is_mutable=Mutable);

    static value_type min_value()       { return channel_traits<value_type>::min_value(); }
    static value_type max_value()       { return channel_traits<value_type>::max_value(); }

    typedef BitField                       bitfield_t;
    typedef typename value_type::integer_t integer_t;

    packed_channel_reference_base(data_ptr_t data_ptr) : _data_ptr(data_ptr) {}
    packed_channel_reference_base(const packed_channel_reference_base& ref) : _data_ptr(ref._data_ptr) {}
    const Derived& operator=(integer_t v) const { set(v); return derived(); }

    const Derived& operator++() const { set(get()+1); return derived(); }
    const Derived& operator--() const { set(get()-1); return derived(); }

    Derived operator++(int) const { Derived tmp=derived(); this->operator++(); return tmp; }
    Derived operator--(int) const { Derived tmp=derived(); this->operator--(); return tmp; }

    template <typename Scalar2> const Derived& operator+=(Scalar2 v) const { set( static_cast<integer_t>(  get() + v )); return derived(); }
    template <typename Scalar2> const Derived& operator-=(Scalar2 v) const { set( static_cast<integer_t>(  get() - v )); return derived(); }
    template <typename Scalar2> const Derived& operator*=(Scalar2 v) const { set( static_cast<integer_t>(  get() * v )); return derived(); }
    template <typename Scalar2> const Derived& operator/=(Scalar2 v) const { set( static_cast<integer_t>(  get() / v )); return derived(); }

    operator integer_t() const { return get(); }
    data_ptr_t operator &() const {return _data_ptr;}
protected:

    typedef  typename detail::num_value_fn< NumBits >::type num_value_t;
    typedef  typename detail::max_value_fn< NumBits >::type max_value_t;

    static const num_value_t num_values = static_cast< num_value_t >( 1 ) << NumBits ;
    static const max_value_t max_val    = static_cast< max_value_t >( num_values - 1 );

#if defined(BOOST_GIL_CONFIG_HAS_UNALIGNED_ACCESS)
    const bitfield_t& get_data()                      const { return *static_cast<const bitfield_t*>(_data_ptr); }
    void              set_data(const bitfield_t& val) const {        *static_cast<      bitfield_t*>(_data_ptr) = val; }
#else
    bitfield_t get_data() const {
        bitfield_t ret;
        static_copy_bytes<sizeof(bitfield_t) >()(gil_reinterpret_cast_c<const unsigned char*>(_data_ptr),gil_reinterpret_cast<unsigned char*>(&ret));
        return ret;
    }
    void set_data(const bitfield_t& val) const {
        static_copy_bytes<sizeof(bitfield_t) >()(gil_reinterpret_cast_c<const unsigned char*>(&val),gil_reinterpret_cast<unsigned char*>(_data_ptr));
    }
#endif

private:
    void set(integer_t value) const {     // can this be done faster??
        this->derived().set_unsafe(((value % num_values) + num_values) % num_values);
    }
    integer_t get() const { return derived().get(); }
    const Derived& derived() const { return static_cast<const Derived&>(*this); }
};
}   // namespace detail

/**
\defgroup PackedChannelReferenceModel packed_channel_reference
\ingroup ChannelModel
\brief Represents a reference proxy to a channel operating over a bit range whose offset is fixed at compile time. Models ChannelConcept
Example:
\code
// Reference to a 2-bit channel starting at bit 1 (i.e. the second bit)
typedef const packed_channel_reference<uint16_t,1,2,true> bits2_1_ref_t;

uint16_t data=0;
bits2_1_ref_t channel_ref(&data);
channel_ref = channel_traits<bits2_1_ref_t>::max_value();   // == 3
assert(data == 6);                                          // == 3<<1 == 6
\endcode
*/

template <typename BitField,        // A type that holds the bits of the pixel from which the channel is referenced. Typically an integral type, like std::uint16_t
          int FirstBit, int NumBits,// Defines the sequence of bits in the data value that contain the channel
          bool Mutable>             // true if the reference is mutable
class packed_channel_reference;

template <typename BitField,        // A type that holds the bits of the pixel from which the channel is referenced. Typically an integral type, like std::uint16_t
          int NumBits,              // Defines the sequence of bits in the data value that contain the channel
          bool Mutable>             // true if the reference is mutable
class packed_dynamic_channel_reference;

/// \ingroup PackedChannelReferenceModel
/// \brief A constant subbyte channel reference whose bit offset is fixed at compile time. Models ChannelConcept
template <typename BitField, int FirstBit, int NumBits>
class packed_channel_reference<BitField,FirstBit,NumBits,false>
   : public detail::packed_channel_reference_base<packed_channel_reference<BitField,FirstBit,NumBits,false>,BitField,NumBits,false> {
    typedef detail::packed_channel_reference_base<packed_channel_reference<BitField,FirstBit,NumBits,false>,BitField,NumBits,false> parent_t;
    friend class packed_channel_reference<BitField,FirstBit,NumBits,true>;

    static const BitField channel_mask = static_cast< BitField >( parent_t::max_val ) << FirstBit;

    void operator=(const packed_channel_reference&);
public:
    typedef const packed_channel_reference<BitField,FirstBit,NumBits,false> const_reference;
    typedef const packed_channel_reference<BitField,FirstBit,NumBits,true>  mutable_reference;
    typedef typename parent_t::integer_t                           integer_t;

    explicit packed_channel_reference(const void* data_ptr) : parent_t(data_ptr) {}
    packed_channel_reference(const packed_channel_reference& ref) : parent_t(ref._data_ptr) {}
    packed_channel_reference(const mutable_reference& ref) : parent_t(ref._data_ptr) {}

    unsigned first_bit() const { return FirstBit; }

    integer_t get() const { return integer_t((this->get_data()&channel_mask) >> FirstBit); }
};

/// \ingroup PackedChannelReferenceModel
/// \brief A mutable subbyte channel reference whose bit offset is fixed at compile time. Models ChannelConcept
template <typename BitField, int FirstBit, int NumBits>
class packed_channel_reference<BitField,FirstBit,NumBits,true>
   : public detail::packed_channel_reference_base<packed_channel_reference<BitField,FirstBit,NumBits,true>,BitField,NumBits,true> {
    typedef detail::packed_channel_reference_base<packed_channel_reference<BitField,FirstBit,NumBits,true>,BitField,NumBits,true> parent_t;
    friend class packed_channel_reference<BitField,FirstBit,NumBits,false>;

    static const BitField channel_mask = static_cast< BitField >( parent_t::max_val ) << FirstBit;

public:
    typedef const packed_channel_reference<BitField,FirstBit,NumBits,false> const_reference;
    typedef const packed_channel_reference<BitField,FirstBit,NumBits,true>  mutable_reference;
    typedef typename parent_t::integer_t                           integer_t;

    explicit packed_channel_reference(void* data_ptr) : parent_t(data_ptr) {}
    packed_channel_reference(const packed_channel_reference& ref) : parent_t(ref._data_ptr) {}

    const packed_channel_reference& operator=(integer_t value) const { assert(value<=parent_t::max_val); set_unsafe(value); return *this; }
    const packed_channel_reference& operator=(const mutable_reference& ref) const { set_from_reference(ref.get_data()); return *this; }
    const packed_channel_reference& operator=(const const_reference&   ref) const { set_from_reference(ref.get_data()); return *this; }

    template <bool Mutable1>
    const packed_channel_reference& operator=(const packed_dynamic_channel_reference<BitField,NumBits,Mutable1>& ref) const { set_unsafe(ref.get()); return *this; }

    unsigned first_bit() const { return FirstBit; }

    integer_t get()                  const { return integer_t((this->get_data()&channel_mask) >> FirstBit); }
    void set_unsafe(integer_t value) const { this->set_data((this->get_data() & ~channel_mask) | (( static_cast< BitField >( value )<<FirstBit))); }
private:
    void set_from_reference(const BitField& other_bits) const { this->set_data((this->get_data() & ~channel_mask) | (other_bits & channel_mask)); }
};

} }  // namespace boost::gil

namespace std {
// We are forced to define swap inside std namespace because on some platforms (Visual Studio 8) STL calls swap qualified.
// swap with 'left bias':
// - swap between proxy and anything
// - swap between value type and proxy
// - swap between proxy and proxy

/// \ingroup PackedChannelReferenceModel
/// \brief swap for packed_channel_reference
template <typename BF, int FB, int NB, bool M, typename R> inline
void swap(const boost::gil::packed_channel_reference<BF,FB,NB,M> x, R& y) {
    boost::gil::swap_proxy<typename boost::gil::packed_channel_reference<BF,FB,NB,M>::value_type>(x,y);
}


/// \ingroup PackedChannelReferenceModel
/// \brief swap for packed_channel_reference
template <typename BF, int FB, int NB, bool M> inline
void swap(typename boost::gil::packed_channel_reference<BF,FB,NB,M>::value_type& x, const boost::gil::packed_channel_reference<BF,FB,NB,M> y) {
    boost::gil::swap_proxy<typename boost::gil::packed_channel_reference<BF,FB,NB,M>::value_type>(x,y);
}

/// \ingroup PackedChannelReferenceModel
/// \brief swap for packed_channel_reference
template <typename BF, int FB, int NB, bool M> inline
void swap(const boost::gil::packed_channel_reference<BF,FB,NB,M> x, const boost::gil::packed_channel_reference<BF,FB,NB,M> y) {
    boost::gil::swap_proxy<typename boost::gil::packed_channel_reference<BF,FB,NB,M>::value_type>(x,y);
}
}   // namespace std

namespace boost { namespace gil {

/**
\defgroup PackedChannelDynamicReferenceModel packed_dynamic_channel_reference
\ingroup ChannelModel
\brief Represents a reference proxy to a channel operating over a bit range whose offset is specified at run time. Models ChannelConcept

Example:
\code
// Reference to a 2-bit channel whose offset is specified at construction time
typedef const packed_dynamic_channel_reference<uint8_t,2,true> bits2_dynamic_ref_t;

uint16_t data=0;
bits2_dynamic_ref_t channel_ref(&data,1);
channel_ref = channel_traits<bits2_dynamic_ref_t>::max_value();     // == 3
assert(data == 6);                                                  // == (3<<1) == 6
\endcode
*/

/// \brief Models a constant subbyte channel reference whose bit offset is a runtime parameter. Models ChannelConcept
///        Same as packed_channel_reference, except that the offset is a runtime parameter
/// \ingroup PackedChannelDynamicReferenceModel
template <typename BitField, int NumBits>
class packed_dynamic_channel_reference<BitField,NumBits,false>
   : public detail::packed_channel_reference_base<packed_dynamic_channel_reference<BitField,NumBits,false>,BitField,NumBits,false> {
    typedef detail::packed_channel_reference_base<packed_dynamic_channel_reference<BitField,NumBits,false>,BitField,NumBits,false> parent_t;
    friend class packed_dynamic_channel_reference<BitField,NumBits,true>;

    unsigned _first_bit;     // 0..7

    void operator=(const packed_dynamic_channel_reference&);
public:
    typedef const packed_dynamic_channel_reference<BitField,NumBits,false> const_reference;
    typedef const packed_dynamic_channel_reference<BitField,NumBits,true>  mutable_reference;
    typedef typename parent_t::integer_t                          integer_t;

    packed_dynamic_channel_reference(const void* data_ptr, unsigned first_bit) : parent_t(data_ptr), _first_bit(first_bit) {}
    packed_dynamic_channel_reference(const const_reference&   ref) : parent_t(ref._data_ptr), _first_bit(ref._first_bit) {}
    packed_dynamic_channel_reference(const mutable_reference& ref) : parent_t(ref._data_ptr), _first_bit(ref._first_bit) {}

    unsigned first_bit() const { return _first_bit; }

    integer_t get() const {
        const BitField channel_mask = static_cast< integer_t >( parent_t::max_val ) <<_first_bit;
        return static_cast< integer_t >(( this->get_data()&channel_mask ) >> _first_bit );
    }
};

/// \brief Models a mutable subbyte channel reference whose bit offset is a runtime parameter. Models ChannelConcept
///        Same as packed_channel_reference, except that the offset is a runtime parameter
/// \ingroup PackedChannelDynamicReferenceModel
template <typename BitField, int NumBits>
class packed_dynamic_channel_reference<BitField,NumBits,true>
   : public detail::packed_channel_reference_base<packed_dynamic_channel_reference<BitField,NumBits,true>,BitField,NumBits,true> {
    typedef detail::packed_channel_reference_base<packed_dynamic_channel_reference<BitField,NumBits,true>,BitField,NumBits,true> parent_t;
    friend class packed_dynamic_channel_reference<BitField,NumBits,false>;

    unsigned _first_bit;

public:
    typedef const packed_dynamic_channel_reference<BitField,NumBits,false> const_reference;
    typedef const packed_dynamic_channel_reference<BitField,NumBits,true>  mutable_reference;
    typedef typename parent_t::integer_t                          integer_t;

    packed_dynamic_channel_reference(void* data_ptr, unsigned first_bit) : parent_t(data_ptr), _first_bit(first_bit) {}
    packed_dynamic_channel_reference(const packed_dynamic_channel_reference& ref) : parent_t(ref._data_ptr), _first_bit(ref._first_bit) {}

    const packed_dynamic_channel_reference& operator=(integer_t value) const { assert(value<=parent_t::max_val); set_unsafe(value); return *this; }
    const packed_dynamic_channel_reference& operator=(const mutable_reference& ref) const {  set_unsafe(ref.get()); return *this; }
    const packed_dynamic_channel_reference& operator=(const const_reference&   ref) const {  set_unsafe(ref.get()); return *this; }

    template <typename BitField1, int FirstBit1, bool Mutable1>
    const packed_dynamic_channel_reference& operator=(const packed_channel_reference<BitField1, FirstBit1, NumBits, Mutable1>& ref) const
        {  set_unsafe(ref.get()); return *this; }

    unsigned first_bit() const { return _first_bit; }

    integer_t get() const {
        const BitField channel_mask = static_cast< integer_t >( parent_t::max_val ) << _first_bit;
        return static_cast< integer_t >(( this->get_data()&channel_mask ) >> _first_bit );
    }

    void set_unsafe(integer_t value) const {
        const BitField channel_mask = static_cast< integer_t >( parent_t::max_val ) << _first_bit;
        this->set_data((this->get_data() & ~channel_mask) | value<<_first_bit);
    }
};
} }  // namespace boost::gil

namespace std {
// We are forced to define swap inside std namespace because on some platforms (Visual Studio 8) STL calls swap qualified.
// swap with 'left bias':
// - swap between proxy and anything
// - swap between value type and proxy
// - swap between proxy and proxy


/// \ingroup PackedChannelDynamicReferenceModel
/// \brief swap for packed_dynamic_channel_reference
template <typename BF, int NB, bool M, typename R> inline
void swap(const boost::gil::packed_dynamic_channel_reference<BF,NB,M> x, R& y) {
    boost::gil::swap_proxy<typename boost::gil::packed_dynamic_channel_reference<BF,NB,M>::value_type>(x,y);
}


/// \ingroup PackedChannelDynamicReferenceModel
/// \brief swap for packed_dynamic_channel_reference
template <typename BF, int NB, bool M> inline
void swap(typename boost::gil::packed_dynamic_channel_reference<BF,NB,M>::value_type& x, const boost::gil::packed_dynamic_channel_reference<BF,NB,M> y) {
    boost::gil::swap_proxy<typename boost::gil::packed_dynamic_channel_reference<BF,NB,M>::value_type>(x,y);
}

/// \ingroup PackedChannelDynamicReferenceModel
/// \brief swap for packed_dynamic_channel_reference
template <typename BF, int NB, bool M> inline
void swap(const boost::gil::packed_dynamic_channel_reference<BF,NB,M> x, const boost::gil::packed_dynamic_channel_reference<BF,NB,M> y) {
    boost::gil::swap_proxy<typename boost::gil::packed_dynamic_channel_reference<BF,NB,M>::value_type>(x,y);
}
}   // namespace std

namespace boost {

template <int NumBits>
struct is_integral<gil::packed_channel_value<NumBits> > : public mpl::true_ {};

template <typename BitField, int FirstBit, int NumBits, bool IsMutable>
struct is_integral<gil::packed_channel_reference<BitField,FirstBit,NumBits,IsMutable> > : public mpl::true_ {};

template <typename BitField, int NumBits, bool IsMutable>
struct is_integral<gil::packed_dynamic_channel_reference<BitField,NumBits,IsMutable> > : public mpl::true_ {};

template <typename BaseChannelValue, typename MinVal, typename MaxVal>
struct is_integral<gil::scoped_channel_value<BaseChannelValue,MinVal,MaxVal> > : public is_integral<BaseChannelValue> {};

} // namespace boost

// \brief Determines the fundamental type which may be used, e.g., to cast from larger to smaller channel types.
namespace boost { namespace gil {
template <typename T>
struct base_channel_type_impl { typedef T type; };

template <int N>
struct base_channel_type_impl<packed_channel_value<N> >
{ typedef typename packed_channel_value<N>::integer_t type; };

template <typename B, int F, int N, bool M>
struct base_channel_type_impl<packed_channel_reference<B, F, N, M> >
{ typedef typename packed_channel_reference<B,F,N,M>::integer_t type; };

template <typename B, int N, bool M>
struct base_channel_type_impl<packed_dynamic_channel_reference<B, N, M> >
{ typedef typename packed_dynamic_channel_reference<B,N,M>::integer_t type; };

template <typename ChannelValue, typename MinV, typename MaxV>
struct base_channel_type_impl<scoped_channel_value<ChannelValue, MinV, MaxV> >
{ typedef ChannelValue type; };

template <typename T>
struct base_channel_type : base_channel_type_impl<typename remove_cv<T>::type > {};

}} //namespace boost::gil

#endif