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/**************************************************************************/
/* */
/* Copyright (c) 2001, 2007 NoMachine, http://www.nomachine.com/. */
/* */
/* NXCOMP, NX protocol compression and NX extensions to this software */
/* are copyright of NoMachine. Redistribution and use of the present */
/* software is allowed according to terms specified in the file LICENSE */
/* which comes in the source distribution. */
/* */
/* Check http://www.nomachine.com/licensing.html for applicability. */
/* */
/* NX and NoMachine are trademarks of NoMachine S.r.l. */
/* */
/* All rights reserved. */
/* */
/**************************************************************************/
#include "TextCompressor.h"
#include "EncodeBuffer.h"
#include "DecodeBuffer.h"
//
// The compression obtained by this class is
// very poor. In newer versions the text is
// simply appended to the encode buffer and
// compressed by leveraging the final stream
// compression.
//
void
TextCompressor::encodeChar(unsigned char ch, EncodeBuffer& encodeBuffer)
{
// encode each successive character of text using
// a predictive model where most of the last 3 characters
// (low order 7 bits of the previous character, plus the
// low order 5 bits of the character before that, plus
// the low order 3 bits of the character before that)
// are used to find the right cache...
CharCache& cache = cache_[key_ % cacheSize_];
if ((key_ >= 128) && (cache.getSize() == 0))
{
// 3rd-order model doesn't have any statistics yet,
// so use the 1st-order one instead
CharCache& cache2 = cache_[(key_ & 0x7f) % cacheSize_];
encodeBuffer.encodeCachedValue((unsigned int) ch, 8, cache2);
cache.insert(ch);
}
else
{
encodeBuffer.encodeCachedValue((unsigned int) ch, 8, cache);
}
key_ = (((key_ & 0x1f) << 7) | ((key_ & 0x380) << 5) | (ch & 0x7f));
}
unsigned char
TextCompressor::decodeChar(DecodeBuffer& decodeBuffer)
{
unsigned char nextChar;
CharCache& cache = cache_[key_ % cacheSize_];
if ((key_ >= 128) && (cache.getSize() == 0))
{
CharCache& cache2 = cache_[(key_ & 0x7f) % cacheSize_];
decodeBuffer.decodeCachedValue(nextChar, 8, cache2);
cache.insert(nextChar);
}
else
{
decodeBuffer.decodeCachedValue(nextChar, 8, cache);
}
key_ = (((key_ & 0x1f) << 7) | ((key_ & 0x380) << 5) | (nextChar & 0x7f));
return nextChar;
}
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