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#include "TextCompressor.H"
#include "EncodeBuffer.H"
#include "DecodeBuffer.H"
#include "util.H"
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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