claw::lzw_decoder< InputBuffer, OutputBuffer > Class Template Reference

A class to help decoding a stream encoded with Lempel-Ziv-Welch (LZW) compression algorithm. More...

#include <lzw_decoder.hpp>

List of all members.

Public Types
typedef InputBuffer	input_buffer_type
	The type of the input buffer.
typedef OutputBuffer	output_buffer_type
	The type of the output buffer.
Public Member Functions
void	decode (input_buffer_type &input, output_buffer_type &output)
	Decode a sequence of LZW compressed datas.
Private Types
typedef std::pair< unsigned int, unsigned int >	word_type
typedef std::vector< word_type >	table_type
Private Member Functions
unsigned int	get_first_symbol (const table_type &table, const unsigned int code, const unsigned int symbols_count) const
	Get the first symbol of a string, represented by a code.
void	decompose (const table_type &table, unsigned int code, const unsigned int symbols_count, output_buffer_type &output) const
	Write a string, represented by a code, in the ouput buffer.

---

Detailed Description

template<typename InputBuffer, typename OutputBuffer>
class claw::lzw_decoder< InputBuffer, OutputBuffer >

A class to help decoding a stream encoded with Lempel-Ziv-Welch (LZW) compression algorithm.

Template parameters:

• InputBuffer The type of the buffer where we read the compressed datas,
• OutputBuffer The type of the buffer where we write the uncompressed datas.

The InputBuffer type must have the following methods:

• bool end_of_data(), tell if the input buffer is empty,
• unsigned int symbols_count(), get the number of different symbols in the uncompressed data,
• unsigned int get_next(), returns the next code and moves to the next symbol.

The OutputBuffer type must have the following methods:

• write( unsigned int ), write a symbol in the output.

Author:

Julien Jorge

Definition at line 61 of file lzw_decoder.hpp.

---

Member Typedef Documentation

template<typename InputBuffer , typename OutputBuffer >

typedef InputBuffer claw::lzw_decoder< InputBuffer, OutputBuffer >::input_buffer_type

The type of the input buffer.

Definition at line 65 of file lzw_decoder.hpp.

template<typename InputBuffer , typename OutputBuffer >

typedef OutputBuffer claw::lzw_decoder< InputBuffer, OutputBuffer >::output_buffer_type

The type of the output buffer.

Definition at line 68 of file lzw_decoder.hpp.

template<typename InputBuffer , typename OutputBuffer >

typedef std::vector<word_type> claw::lzw_decoder< InputBuffer, OutputBuffer >::table_type [private]

Definition at line 72 of file lzw_decoder.hpp.

template<typename InputBuffer , typename OutputBuffer >

typedef std::pair<unsigned int, unsigned int> claw::lzw_decoder< InputBuffer, OutputBuffer >::word_type [private]

Definition at line 71 of file lzw_decoder.hpp.

---

Member Function Documentation

template<typename InputBuffer , typename OutputBuffer >

void claw::lzw_decoder< InputBuffer, OutputBuffer >::decode	(	input_buffer_type &	input,
		output_buffer_type &	output
	)

Decode a sequence of LZW compressed datas.

Parameters:

	input	Where we read the compressed datas.
	output	Where we write uncompressed datas.

Definition at line 40 of file lzw_decoder.tpp.

{
  const unsigned int symbols_count = input.symbols_count();

  table_type table;
  unsigned int table_size = 0;

  unsigned int prefix = input.get_next();

  if ( !input.end_of_data() )
    {
      while ( !input.end_of_data() )
        {
          unsigned int suffix = input.get_next();

          if (!input.end_of_data() )
            {
              unsigned int new_suffix;

              if ( suffix < table_size + symbols_count )
                new_suffix = get_first_symbol(table, suffix, symbols_count);
              else
                new_suffix = get_first_symbol(table, prefix, symbols_count);

              table.push_back( word_type(prefix, new_suffix) );
              ++table_size;
              input.new_code(table_size + symbols_count);

              decompose( table, prefix, symbols_count, output );
              prefix = suffix;
            }
        }

      decompose( table, prefix, symbols_count, output );
    }
} // lzw_decoder::decode()

template<typename InputBuffer , typename OutputBuffer >

void claw::lzw_decoder< InputBuffer, OutputBuffer >::decompose	(	const table_type &	table,
		unsigned int	code,
		const unsigned int	symbols_count,
		output_buffer_type &	output
	)			const [private]

Write a string, represented by a code, in the ouput buffer.

Parameters:

	table	The table of codes.
	code	The code of the string to write.
	symbols_count	The count of atomic codes.
	output	Where we write the uncompressed datas.

Definition at line 107 of file lzw_decoder.tpp.

{
  std::list<unsigned int> result;

  while ( code >= symbols_count )
    {
      result.push_front( table[code - symbols_count].second );
      code = table[code - symbols_count].first;
    }
  
  result.push_front(code);

  std::list<unsigned int>::const_iterator it;

  for (it=result.begin(); it!=result.end(); ++it)
    output.write( *it );

} // lzw_decoder::decompose()

template<typename InputBuffer , typename OutputBuffer >

unsigned int claw::lzw_decoder< InputBuffer, OutputBuffer >::get_first_symbol	(	const table_type &	table,
		const unsigned int	code,
		const unsigned int	symbols_count
	)			const [private]

Get the first symbol of a string, represented by a code.

Parameters:

	table	The table of codes.
	code	The code of the string from which we want the first symbol.
	symbols_count	The count of atomic codes.

Definition at line 86 of file lzw_decoder.tpp.

{
  unsigned int result = code;

  while ( result >= symbols_count )
    result = table[result - symbols_count].first;

  return result;
} // lzw_decoder::get_first_symbol()

---

The documentation for this class was generated from the following files:

• lzw_decoder.hpp
• impl/lzw_decoder.tpp