dlib C++ Library - entropy_decoder_model_kernel_1.h

    // Copyright (C) 2004  Davis E. King (davisking@users.sourceforge.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_ENTROPY_DECODER_MODEL_KERNEl_1_
    #define DLIB_ENTROPY_DECODER_MODEL_KERNEl_1_

    #include "../algs.h"
    #include "entropy_decoder_model_kernel_abstract.h"
    #include "../assert.h"

    namespace dlib
    {

        template <
            unsigned long alphabet_size,
            typename entropy_decoder,
            typename cc
            >
        class entropy_decoder_model_kernel_1
        {
            /*!
                REQUIREMENTS ON cc
                    cc is an implementation of conditioning_class/conditioning_class_kernel_abstract.h
                    cc::get_alphabet_size() == alphabet_size+1

                INITIAL VALUE
                    Initially this object's finite context model is empty

                CONVENTION
                    &get_entropy_decoder() == coder
                    &order_0.get_global_state() == &gs

                    This is an order-0 model. The last symbol in the order-0 context is
                    an escape into the order minus 1 context.
            !*/

        public:

            typedef entropy_decoder entropy_decoder_type;

            entropy_decoder_model_kernel_1 (
                entropy_decoder& coder
            );

            virtual ~entropy_decoder_model_kernel_1 (
            );

            inline void clear(
            );

            inline void decode (
                unsigned long& symbol
            );

            entropy_decoder& get_entropy_decoder (
            ) { return coder; }

            static unsigned long get_alphabet_size (
            ) { return alphabet_size; }

        private:

            entropy_decoder& coder;
            typename cc::global_state_type gs;
            cc order_0;

            // restricted functions
            entropy_decoder_model_kernel_1(entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>&);        // copy constructor
            entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>& operator=(entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>&);    // assignment operator

        };

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
        // member function definitions
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_decoder,
            typename cc
            >
        entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>::
        entropy_decoder_model_kernel_1 (
            entropy_decoder& coder_
        ) :
            coder(coder_),
            order_0(gs)
        {
            COMPILE_TIME_ASSERT( 1 < alphabet_size && alphabet_size < 65535 );
        }

    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_decoder,
            typename cc
            >
        entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>::
        ~entropy_decoder_model_kernel_1 (
        )
        {
        }

    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_decoder,
            typename cc
            >
        void entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>::
        clear(
        )
        {
            order_0.clear();
        }

    // ----------------------------------------------------------------------------------------

        template <
            unsigned long alphabet_size,
            typename entropy_decoder,
            typename cc
            >
        void entropy_decoder_model_kernel_1<alphabet_size,entropy_decoder,cc>::
        decode (
            unsigned long& symbol
        )
        {
            unsigned long current_symbol, low_count, high_count, target;

            // look in the order-0 context
            target = coder.get_target(order_0.get_total());
            order_0.get_symbol(target,current_symbol,low_count,high_count);

            // have coder decode the next symbol
            coder.decode(low_count,high_count);

            // if current_symbol is not an escape from the order-0 context
            if (current_symbol != alphabet_size)
            {
                // update the count for this symbol
                order_0.increment_count(current_symbol,2);

                symbol = current_symbol;
                return;
            }

            // update the count for the escape symbol
            order_0.increment_count(alphabet_size);

            // go into the order minus one context
            target = coder.get_target(alphabet_size);
            coder.decode(target,target+1);

            // update the count for this symbol in the order-0 context
            order_0.increment_count(target,2);

            symbol = target;

        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_ENTROPY_DECODER_MODEL_KERNEl_1_