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-rw-r--r--nxcomp/TextCompressor.cpp77
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diff --git a/nxcomp/TextCompressor.cpp b/nxcomp/TextCompressor.cpp
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+/**************************************************************************/
+/* */
+/* Copyright (c) 2001, 2010 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 Medialogic S.p.A. */
+/* */
+/* 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;
+}