coco
131 lines
4.1 KiB
C++
131 lines
4.1 KiB
C++
// Copyright (C) 2005 Davis E. King (davis@dlib.net)
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// License: Boost Software License See LICENSE.txt for the full license.
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#undef DLIB_LZP_BUFFER_KERNEl_ABSTRACT_
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#ifdef DLIB_LZP_BUFFER_KERNEl_ABSTRACT_
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#include "../algs.h"
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namespace dlib
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{
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class lzp_buffer
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{
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/*!
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INITIAL VALUE
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size() == some value defined by the constructor argument
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Initially this object is at some predefined empty or ground state.
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for all i: (*this)[i] == 0
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WHAT THIS OBJECT REPRESENTS
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This object represents some varation on the LZP algorithm
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described by Charles Bloom in his paper "LZP: a new data
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compression algorithm"
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The LZP algorithm is a lot like lz77 except there is no need to pass
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the location of matches in the history buffer to the decoder because
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LZP uses the data it has already seen to predict the location of the
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next match.
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NOTE
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The add() and predict_match() functions must be called in the same
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order by the coder and decoder. If they aren't the state of the
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lzp_buffer objects in the coder and decoder may differ and the decoder
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won't be able to correctly decode the data stream.
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!*/
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public:
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explicit lzp_buffer (
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unsigned long buffer_size
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);
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/*!
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requires
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- 10 < buffer_size < 32
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ensures
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- #*this is properly initialized
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- #size() == 2^buffer_size
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throws
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- std::bad_alloc
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!*/
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virtual ~lzp_buffer (
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);
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/*!
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ensures
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- any resources associated with *this have been released
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!*/
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void clear(
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);
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/*!
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ensures
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- #*this has its initial value
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throws
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- std::bad_alloc
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if this exception is thrown then #*this is unusable
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until clear() is called and succeeds
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!*/
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void add (
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unsigned char symbol
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);
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/*!
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ensures
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- shifts everything in the history buffer left 1.
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(i.e. #(*this)[i+1] == (*this)[i])
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- #(*this)[0] == symbol
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throws
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- std::bad_alloc
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if this exception is thrown then #*this is unusable
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until clear() is called and succeeds
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!*/
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unsigned long predict_match (
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unsigned long& index
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);
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/*!
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ensures
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- updates the prediction for the current context.
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(the current context is the last few symbols seen. i.e. (*this)[0],
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(*this)[1], etc.)
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- if (*this can generate a prediction) then
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- #index == the predicted location of a match in the history buffer.
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(i.e. (*this)[#index] is the first symbol of the predicted match)
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- returns the order this prediction came from
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- else
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- returns 0
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throws
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- std::bad_alloc
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if this exception is thrown then #*this is unusable
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until clear() is called and succeeds
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!*/
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size_t size (
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) const;
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/*!
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ensures
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- returns the size of the history buffer
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!*/
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unsigned char operator[] (
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unsigned long index
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) const;
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/*!
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requires
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- index < size()
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ensures
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- returns the symbol at the given index in the history buffer
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!*/
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private:
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// restricted functions
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lzp_buffer(const lzp_buffer&); // copy constructor
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lzp_buffer& operator=(const lzp_buffer&); // assignment operator
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};
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}
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#endif // DLIB_LZP_BUFFER_KERNEl_ABSTRACT_
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