coco
264 lines
7.7 KiB
C++
264 lines
7.7 KiB
C++
// Copyright (C) 2004 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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#ifndef DLIB_LZ77_BUFFER_KERNEl_1_
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#define DLIB_LZ77_BUFFER_KERNEl_1_
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#include "lz77_buffer_kernel_abstract.h"
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#include "../algs.h"
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namespace dlib
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{
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template <
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typename sliding_buffer
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>
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class lz77_buffer_kernel_1
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{
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/*!
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REQUIREMENTS ON sliding_buffer
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sliding_buffer must be an implementation of sliding_buffer/sliding_buffer_kernel_abstract.h
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INITIAL VALUE
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history_limit == defined by constructor arguments
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lookahead_limit == defined by constructor arguments
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history_size == 0
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lookahead_size == 0
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buffer.size() == history_limit + lookahead_limit
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CONVENTION
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history_limit == get_history_buffer_limit()
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lookahead_limit == get_lookahead_buffer_limit()
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history_size == get_history_buffer_size()
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lookahead_limit == get_lookahead_buffer_size()
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buffer.size() == history_limit + lookahead_limit
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lookahead_buffer(i) == buffer[lookahead_limit-1-i]
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history_buffer(i) == buffer[lookahead_limit+i]
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!*/
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public:
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lz77_buffer_kernel_1 (
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unsigned long total_limit_,
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unsigned long lookahead_limit_
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);
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virtual ~lz77_buffer_kernel_1 (
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) {}
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void clear(
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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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void find_match (
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unsigned long& index,
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unsigned long& length,
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unsigned long min_match_length
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);
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inline unsigned long get_history_buffer_limit (
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) const { return history_limit; }
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inline unsigned long get_lookahead_buffer_limit (
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) const { return lookahead_limit; }
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inline unsigned long get_history_buffer_size (
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) const { return history_size; }
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inline unsigned long get_lookahead_buffer_size (
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) const { return lookahead_size; }
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inline unsigned char lookahead_buffer (
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unsigned long index
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) const { return buffer[lookahead_limit-1-index]; }
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inline unsigned char history_buffer (
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unsigned long index
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) const { return buffer[lookahead_limit+index]; }
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inline void shift_buffers (
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unsigned long N
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) { shift_buffer(N); }
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private:
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inline void shift_buffer (
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unsigned long N
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)
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/*!
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requires
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- N <= lookahead_size
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ensuers
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- #lookahead_size == lookahead_size - N
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- if (history_size+N < history_limit) then
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- #history_size == history_size+N
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- else
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- #history_size == history_limit
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- for all i where 0 <= i < N:
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#history_buffer(N-1-i) == lookahead_buffer(i)
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- for all i where 0 <= i < #history_size-N:
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#history_buffer(N+i) == history_buffer(i)
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- for all i where 0 <= i < #lookahead_size
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#lookahead_buffer(i) == lookahead_buffer(N+i)
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!*/
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{
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unsigned long temp = history_size+N;
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buffer.rotate_left(N);
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lookahead_size -= N;
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if (temp < history_limit)
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history_size = temp;
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else
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history_size = history_limit;
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}
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// member data
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sliding_buffer buffer;
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unsigned long lookahead_limit;
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unsigned long history_limit;
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unsigned long lookahead_size;
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unsigned long history_size;
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// restricted functions
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lz77_buffer_kernel_1(lz77_buffer_kernel_1<sliding_buffer>&); // copy constructor
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lz77_buffer_kernel_1<sliding_buffer>& operator=(lz77_buffer_kernel_1<sliding_buffer>&); // assignment operator
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};
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// ----------------------------------------------------------------------------------------
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// ----------------------------------------------------------------------------------------
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// member function definitions
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// ----------------------------------------------------------------------------------------
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// ----------------------------------------------------------------------------------------
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template <
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typename sliding_buffer
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>
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lz77_buffer_kernel_1<sliding_buffer>::
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lz77_buffer_kernel_1 (
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unsigned long total_limit_,
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unsigned long lookahead_limit_
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) :
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lookahead_size(0),
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history_size(0)
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{
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buffer.set_size(total_limit_);
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lookahead_limit = lookahead_limit_;
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history_limit = buffer.size() - lookahead_limit_;
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}
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// ----------------------------------------------------------------------------------------
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template <
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typename sliding_buffer
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>
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void lz77_buffer_kernel_1<sliding_buffer>::
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clear(
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)
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{
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lookahead_size = 0;
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history_size = 0;
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}
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// ----------------------------------------------------------------------------------------
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template <
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typename sliding_buffer
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>
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void lz77_buffer_kernel_1<sliding_buffer>::
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add (
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unsigned char symbol
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)
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{
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if (lookahead_size == lookahead_limit)
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{
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shift_buffer(1);
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}
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buffer[lookahead_limit-1-lookahead_size] = symbol;
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++lookahead_size;
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}
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// ----------------------------------------------------------------------------------------
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template <
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typename sliding_buffer
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>
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void lz77_buffer_kernel_1<sliding_buffer>::
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find_match (
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unsigned long& index,
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unsigned long& length,
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unsigned long min_match_length
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)
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{
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unsigned long hpos = history_size; // current position in the history buffer
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unsigned long lpos = 0; // current position in the lookahead buffer
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unsigned long match_length = 0; // the length of the longest match we find
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unsigned long match_index = 0; // the index of the longest match we find
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// try to find a match
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while (hpos != 0)
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{
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--hpos;
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// if we are finding a match
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if (history_buffer(hpos) == lookahead_buffer(lpos))
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{
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++lpos;
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// if we have found a match that is as long as the lookahead buffer
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// then we are done
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if (lpos == lookahead_size)
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break;
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}
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// else if we found the end of a match
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else if (lpos > 0)
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{
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// if this match is longer than the last match we saw
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if (lpos > match_length)
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{
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match_length = lpos;
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match_index = hpos + lpos;
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}
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lpos = 0;
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}
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} // while (hpos != 0)
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// if we found a match at the end of the loop that is greater than
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// the match in match_index
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if (lpos > match_length)
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{
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match_length = lpos;
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match_index = hpos + lpos - 1;
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}
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// if we found a match that was long enough then report it
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if (match_length >= min_match_length)
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{
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shift_buffer(match_length);
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index = match_index;
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length = match_length;
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}
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else
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{
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length = 0;
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}
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}
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// ----------------------------------------------------------------------------------------
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}
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#endif // DLIB_LZ77_BUFFER_KERNEl_1_
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