dlib C++ Library - compress_stream_kernel_3.h

    // Copyright (C) 2005  Davis E. King (davisking@users.sourceforge.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_COMPRESS_STREAM_KERNEl_3_
    #define DLIB_COMPRESS_STREAM_KERNEl_3_

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

    namespace dlib
    {

        template <
            typename lzp_buf,
            typename crc32,
            unsigned long buffer_size
            >
        class compress_stream_kernel_3
        {
            /*!
                REQUIREMENTS ON lzp_buf
                    is an implementation of lzp_buffer/lzp_buffer_kernel_abstract.h

                REQUIREMENTS ON buffer_size
                    10 < buffer_size < 32

                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

                    This implementation uses the lzp_buffer and writes out matches
                    in a byte aligned format.

            !*/

        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_3 (
            )
            {
                COMPILE_TIME_ASSERT(10 < buffer_size && buffer_size < 32);
            }

            ~compress_stream_kernel_3 (
            )
            {}

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

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

        private:

            inline void write (
                unsigned char symbol
            ) const
            {
                if (out->sputn(reinterpret_cast<char*>(&symbol),1)==0)
                    throw std::ios_base::failure("error writing to output stream in compress_stream_kernel_3");
            }

            inline void decode (
                unsigned char& symbol,
                unsigned char& flag
            ) const
            {
                if (count == 0)
                {
                    if (((size_t)in->sgetn(reinterpret_cast<char*>(buffer),sizeof(buffer)))!=sizeof(buffer))
                        throw decompression_error("Error detected in compressed data stream.");
                    count = 8;
                }
                --count;
                symbol = buffer[8-count];
                flag = buffer[0] >> 7;
                buffer[0] <<= 1;
            }

            inline void encode (
                unsigned char symbol,
                unsigned char flag
            ) const
            /*!
                requires
                    - 0 <= flag <= 1
                ensures
                    - writes symbol with the given one bit flag
            !*/
            {
                // add this symbol and flag to the buffer
                ++count;
                buffer[0] <<= 1;
                buffer[count] = symbol;
                buffer[0] |= flag;

                if (count == 8)
                {
                    if (((size_t)out->sputn(reinterpret_cast<char*>(buffer),sizeof(buffer)))!=sizeof(buffer))
                        throw std::ios_base::failure("error writing to output stream in compress_stream_kernel_3");
                    count = 0;
                    buffer[0] = 0;
                }
            }

            void clear (
            ) const
            /*!
                ensures
                    - resets the buffers
            !*/
            {
                count = 0;
            }

            void flush (
            ) const
            /*!
                ensures
                    - flushes any data in the buffers to out
            !*/
            {
                if (count != 0)
                {
                    buffer[0] <<= (8-count);
                    if (((size_t)out->sputn(reinterpret_cast<char*>(buffer),sizeof(buffer)))!=sizeof(buffer))
                        throw std::ios_base::failure("error writing to output stream in compress_stream_kernel_3");
                }
            }

            mutable unsigned int count;
            // count tells us how many bytes are buffered in buffer and how many flag
            // bit are currently in buffer[0]
            mutable unsigned char buffer[9];
            // buffer[0] holds the flag bits to be writen.
            // the rest of the buffer holds the bytes to be writen.

            mutable std::streambuf* in;
            mutable std::streambuf* out;

            // restricted functions
            compress_stream_kernel_3(compress_stream_kernel_3<lzp_buf,crc32,buffer_size>&);        // copy constructor
            compress_stream_kernel_3<lzp_buf,crc32,buffer_size>& operator=(compress_stream_kernel_3<lzp_buf,crc32,buffer_size>&);    // assignment operator

        };

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

        template <
            typename lzp_buf,
            typename crc32,
            unsigned long buffer_size
            >
        void compress_stream_kernel_3<lzp_buf,crc32,buffer_size>::
        compress (
            std::istream& in_,
            std::ostream& out_
        ) const
        {
            in = in_.rdbuf();
            out = out_.rdbuf();
            clear();

            crc32 crc;

            lzp_buf buffer(buffer_size);

            std::streambuf::int_type temp = in->sbumpc();
            unsigned long index;
            unsigned char symbol;
            unsigned char length;

            while (temp != EOF)
            {
                symbol = static_cast<unsigned char>(temp);
                if (buffer.predict_match(index))
                {
                    if (buffer[index] == symbol)
                    {
                        // this is a match so we must find out how long it is
                        length = 1;

                        buffer.add(symbol);
                        crc.add(symbol);

                        temp = in->sbumpc();
                        while (length < 255)
                        {
                            if (temp == EOF)
                            {
                                break;
                            }
                            else if (static_cast<unsigned long>(length) >= index)
                            {
                                break;
                            }
                            else if (static_cast<unsigned char>(temp) == buffer[index])
                            {
                                ++length;
                                buffer.add(static_cast<unsigned char>(temp));
                                crc.add(static_cast<unsigned char>(temp));
                                temp = in->sbumpc();
                            }
                            else
                            {
                                break;
                            }
                        }

                        encode(length,1);
                    }
                    else
                    {
                        // this is also not a match
                        encode(symbol,0);
                        buffer.add(symbol);
                        crc.add(symbol);

                        // get the next symbol
                        temp = in->sbumpc();
                    }
                }
                else
                {
                    // there wasn't a match so just write this symbol
                    encode(symbol,0);
                    buffer.add(symbol);
                    crc.add(symbol);

                    // get the next symbol
                    temp = in->sbumpc();
                }
            }

            // use a match of zero length to indicate EOF
            encode(0,1);

            // 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);

            encode(byte1,0);
            encode(byte2,0);
            encode(byte3,0);
            encode(byte4,0);

            flush();
        }

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

        template <
            typename lzp_buf,
            typename crc32,
            unsigned long buffer_size
            >
        void compress_stream_kernel_3<lzp_buf,crc32,buffer_size>::
        decompress (
            std::istream& in_,
            std::ostream& out_
        ) const
        {
            in = in_.rdbuf();
            out = out_.rdbuf();
            clear();

            crc32 crc;

            lzp_buf buffer(buffer_size);

            unsigned long index = 0;
            unsigned char symbol;
            unsigned char length;
            unsigned char flag;

            decode(symbol,flag);
            while (flag == 0 || symbol != 0)
            {
                buffer.predict_match(index);

                if (flag == 1)
                {
                    length = symbol;
                    do
                    {
                        --length;
                        symbol = buffer[index];
                        write(symbol);
                        buffer.add(symbol);
                        crc.add(symbol);
                    } while (length != 0);
                }
                else
                {
                    // this is just a literal
                    write(symbol);
                    buffer.add(symbol);
                    crc.add(symbol);
                }
                decode(symbol,flag);
            }

            // now get the checksum and make sure it matches
            unsigned char byte1;
            unsigned char byte2;
            unsigned char byte3;
            unsigned char byte4;

            decode(byte1,flag);
            if (flag != 0)
                throw decompression_error("Error detected in compressed data stream.");
            decode(byte2,flag);
            if (flag != 0)
                throw decompression_error("Error detected in compressed data stream.");
            decode(byte3,flag);
            if (flag != 0)
                throw decompression_error("Error detected in compressed data stream.");
            decode(byte4,flag);
            if (flag != 0)
                throw decompression_error("Error detected in compressed data stream.");

            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.");

        }

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

    }

    #endif // DLIB_COMPRESS_STREAM_KERNEl_3_