dlib C++ Library - compress_stream_kernel_1.h

    // Copyright (C) 2003  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_COMPRESS_STREAM_KERNEl_1_
    #define DLIB_COMPRESS_STREAM_KERNEl_1_

    #include "../algs.h"
    #include <iostream>
    #include <streambuf>
    #include <cstdio>
    #include "compress_stream_kernel_abstract.h"

    namespace dlib
    {

        template <
            typename fce,
            typename fcd,
            typename crc32
            >
        class compress_stream_kernel_1
        {
            /*!
                REQUIREMENTS ON fce
                    is an implementation of entropy_encoder_model/entropy_encoder_model_kernel_abstract.h
                    the alphabet_size of fce must be 257.
                    fce and fcd share the same kernel number.

                REQUIREMENTS ON fcd
                    is an implementation of entropy_decoder_model/entropy_decoder_model_kernel_abstract.h
                    the alphabet_size of fcd must be 257.
                    fce and fcd share the same kernel number.

                REQUIREMENTS ON crc32
                    is an implementation of crc32/crc32_kernel_abstract.h

                INITIAL VALUE
                    this object has no state

                CONVENTION
                    this object has no state
            !*/

            const static unsigned long eof_symbol = 256;

        public:

            class decompression_error : public dlib::error
            {
                public:
                    decompression_error(
                        const char* i
                    ) :
                        dlib::error(std::string(i))
                    {}

                    decompression_error(
                        const std::string& i
                    ) :
                        dlib::error(i)
                    {}
            };

            compress_stream_kernel_1 (
            )
            {}

            ~compress_stream_kernel_1 (
            )
            {}

            void compress (
                std::istream& in,
                std::ostream& out
            ) const;

            void decompress (
                std::istream& in,
                std::ostream& out
            ) const;

        private:

            // restricted functions
            compress_stream_kernel_1(compress_stream_kernel_1&);        // copy constructor
            compress_stream_kernel_1& operator=(compress_stream_kernel_1&);    // assignment operator

        };

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

        template <
            typename fce,
            typename fcd,
            typename crc32
            >
        void compress_stream_kernel_1<fce,fcd,crc32>::
        compress (
            std::istream& in_,
            std::ostream& out_
        ) const
        {
            std::streambuf::int_type temp;

            std::streambuf& in = *in_.rdbuf();

            typename fce::entropy_encoder_type coder;
            coder.set_stream(out_);

            fce model(coder);

            crc32 crc;

            unsigned long count = 0;

            while (true)
            {
                // write out a known value every 20000 symbols
                if (count == 20000)
                {
                    count = 0;
                    coder.encode(1500,1501,8000);
                }
                ++count;

                // get the next character
                temp = in.sbumpc();

                // if we have hit EOF then encode the marker symbol
                if (temp != EOF)
                {
                    // encode the symbol
                    model.encode(static_cast<unsigned long>(temp));
                    crc.add(static_cast<unsigned char>(temp));
                    continue;
                }
                else
                {
                    model.encode(eof_symbol);

                    // now write the checksum
                    unsigned long checksum = crc.get_checksum();
                    unsigned char byte1 = static_cast<unsigned char>((checksum>>24)&0xFF);
                    unsigned char byte2 = static_cast<unsigned char>((checksum>>16)&0xFF);
                    unsigned char byte3 = static_cast<unsigned char>((checksum>>8)&0xFF);
                    unsigned char byte4 = static_cast<unsigned char>((checksum)&0xFF);

                    model.encode(byte1);
                    model.encode(byte2);
                    model.encode(byte3);
                    model.encode(byte4);

                    break;
                }
            }
        }

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

        template <
            typename fce,
            typename fcd,
            typename crc32
            >
        void compress_stream_kernel_1<fce,fcd,crc32>::
        decompress (
            std::istream& in_,
            std::ostream& out_
        ) const
        {

            std::streambuf& out = *out_.rdbuf();

            typename fcd::entropy_decoder_type coder;
            coder.set_stream(in_);

            fcd model(coder);

            unsigned long symbol;
            unsigned long count = 0;

            crc32 crc;

            // decode until we hit the marker symbol
            while (true)
            {
                // make sure this is the value we expect
                if (count == 20000)
                {
                    if (coder.get_target(8000) != 1500)
                    {
                        throw decompression_error("Error detected in compressed data stream.");
                    }
                    count = 0;
                    coder.decode(1500,1501);
                }
                ++count;

                // decode the next symbol
                model.decode(symbol);
                if (symbol != eof_symbol)
                {
                    crc.add(static_cast<unsigned char>(symbol));
                    // write this symbol to out
                    if (out.sputc(static_cast<char>(symbol)) != static_cast<int>(symbol))
                    {
                        throw std::ios::failure("error occurred in compress_stream_kernel_1::decompress");
                    }
                    continue;
                }
                else
                {
                    // we read eof from the encoded data.  now we just have to check the checksum and we are done.
                    unsigned char byte1;
                    unsigned char byte2;
                    unsigned char byte3;
                    unsigned char byte4;

                    model.decode(symbol); byte1 = static_cast<unsigned char>(symbol);
                    model.decode(symbol); byte2 = static_cast<unsigned char>(symbol);
                    model.decode(symbol); byte3 = static_cast<unsigned char>(symbol);
                    model.decode(symbol); byte4 = static_cast<unsigned char>(symbol);

                    unsigned long checksum = byte1;
                    checksum <<= 8;
                    checksum |= byte2;
                    checksum <<= 8;
                    checksum |= byte3;
                    checksum <<= 8;
                    checksum |= byte4;

                    if (checksum != crc.get_checksum())
                        throw decompression_error("Error detected in compressed data stream.");

                    break;
                }
            } // while (true)

        }

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

    }

    #endif // DLIB_COMPRESS_STREAM_KERNEl_1_