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// Boost string_algo library example file ---------------------------------//

// Copyright Pavol Droba 2002-2003. Use, modification and

// distribution is subject to 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)

// See http://www.boost.org for updates, documentation, and revision history.

RLE compression using replace framework. Goal is to compress a sequence of

repeating characters into 3 bytes ( repeat mark, character and repetition count ).

For simplification, it works only on numeric-value sequences.

#include <string>

#include <iostream>

#include <limits>

#include <iterator>

#include <boost/algorithm/string/find_format.hpp>

#include <boost/algorithm/string/finder.hpp>

using namespace std;

using namespace boost;

// replace mark specification, specialize for a specific element type

template< typename T > T repeat_mark() { return (std::numeric_limits<T>::max)(); };

// Compression -----------------------------------------------------------------------

// compress finder -rle

Find a sequence which can be compressed. It has to be at least 3-character long

sequence of repetitive characters

struct find_compressF

{

// Construction

find_compressF() {}

// Operation

template<typename ForwardIteratorT>

iterator_range<ForwardIteratorT> operator()(

ForwardIteratorT Begin,

ForwardIteratorT End ) const

{

typedef ForwardIteratorT input_iterator_type;

typedef typename std::iterator_traits<input_iterator_type>::value_type value_type;

typedef iterator_range<input_iterator_type> result_type;

// begin of the matching segment

input_iterator_type MStart=End;

// Repetition counter

value_type Cnt=0;

// Search for a sequence of repetitive characters

for(input_iterator_type It=Begin; It!=End;)

{

input_iterator_type It2=It++;

if ( It==End || Cnt>=(std::numeric_limits<value_type>::max)() )

{

return result_type( MStart, It );

}

if ( *It==*It2 )

{

if ( MStart==End )

{

// Mark the start

MStart=It2;

}

// Increate repetition counter

Cnt++;

}

else

{

if ( MStart!=End )

{

if ( Cnt>2 )

return result_type( MStart, It );

else

{

MStart=End;

Cnt=0;

}

return result_type( End, End );

}

};

// rle compress format

Transform a sequence into repeat mark, character and count

template<typename SeqT>

struct format_compressF

{

private:

typedef SeqT result_type;

typedef typename SeqT::value_type value_type;

public:

// Construction

format_compressF() {};

// Operation

template< typename ReplaceT >

result_type operator()( const ReplaceT& Replace ) const

{

SeqT r;

if(!Replace.empty())

{

r.push_back( repeat_mark<value_type>() );

r.push_back( *(Replace.begin()) );

r.push_back( value_type( Replace.size() ) );

}

return r;

}

};

// Decompression -----------------------------------------------------------------------

// find decompress-rle functor

find a repetition block

struct find_decompressF

{

// Construction

find_decompressF() {}

// Operation

template<typename ForwardIteratorT>

iterator_range<ForwardIteratorT> operator()(

ForwardIteratorT Begin,

ForwardIteratorT End ) const

{

typedef ForwardIteratorT input_iterator_type;

typedef typename std::iterator_traits<input_iterator_type>::value_type value_type;

typedef iterator_range<input_iterator_type> result_type;

for(input_iterator_type It=Begin; It!=End; It++)

{

if( *It==repeat_mark<value_type>() )

{

// Repeat mark found, extract body

input_iterator_type It2=It++;

if ( It==End ) break;

It++;

if ( It==End ) break;

It++;

return result_type( It2, It );

}

return result_type( End, End );

}

};

// rle decompress format

transform a repetition block into a sequence of characters

template< typename SeqT >

struct format_decompressF

{

private:

typedef SeqT result_type;

typedef typename SeqT::value_type value_type;

public:

// Construction

format_decompressF() {};

// Operation

template< typename ReplaceT >

result_type operator()( const ReplaceT& Replace ) const

{

SeqT r;

if(!Replace.empty())

{

// extract info

typename ReplaceT::const_iterator It=Replace.begin();

value_type Value=*(++It);

value_type Repeat=*(++It);

for( value_type Index=0; Index<Repeat; Index++ ) r.push_back( Value );

}

return r;

}

};

int main()

{

cout << "* RLE Compression Example *" << endl << endl;

string original("123_AA_*ZZZZZZZZZZZZZZ*34");

// copy compression

string compress=find_format_all_copy(

original,

find_compressF(),

format_compressF<string>() );

cout << "Compressed string: " << compress << endl;

// Copy decompression

string decompress=find_format_all_copy(

compress,

find_decompressF(),

format_decompressF<string>() );

cout << "Decompressed string: " << decompress << endl;

// in-place compression

find_format_all(

original,

find_compressF(),

format_compressF<string>() );

cout << "Compressed string: " << original << endl;

// in-place decompression

find_format_all(

original,

find_decompressF(),

format_decompressF<string>() );

cout << "Decompressed string: " << original << endl;

cout << endl;

return 0;

}

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