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Unified Diff: xz/src/liblzma/rangecoder/range_common.h

Issue 2869016: Add an unpatched version of xz, XZ Utils, to /trunk/deps/third_party (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/deps/third_party/
Patch Set: Created 10 years, 6 months ago
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Index: xz/src/liblzma/rangecoder/range_common.h
===================================================================
--- xz/src/liblzma/rangecoder/range_common.h (revision 0)
+++ xz/src/liblzma/rangecoder/range_common.h (revision 0)
@@ -0,0 +1,73 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file range_common.h
+/// \brief Common things for range encoder and decoder
+///
+// Authors: Igor Pavlov
+// Lasse Collin
+//
+// This file has been put into the public domain.
+// You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef LZMA_RANGE_COMMON_H
+#define LZMA_RANGE_COMMON_H
+
+#ifdef HAVE_CONFIG_H
+# include "common.h"
+#endif
+
+
+///////////////
+// Constants //
+///////////////
+
+#define RC_SHIFT_BITS 8
+#define RC_TOP_BITS 24
+#define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS)
+#define RC_BIT_MODEL_TOTAL_BITS 11
+#define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS)
+#define RC_MOVE_BITS 5
+
+
+////////////
+// Macros //
+////////////
+
+// Resets the probability so that both 0 and 1 have probability of 50 %
+#define bit_reset(prob) \
+ prob = RC_BIT_MODEL_TOTAL >> 1
+
+// This does the same for a complete bit tree.
+// (A tree represented as an array.)
+#define bittree_reset(probs, bit_levels) \
+ for (uint32_t bt_i = 0; bt_i < (1 << (bit_levels)); ++bt_i) \
+ bit_reset((probs)[bt_i])
+
+
+//////////////////////
+// Type definitions //
+//////////////////////
+
+/// \brief Type of probabilities used with range coder
+///
+/// This needs to be at least 12-bit integer, so uint16_t is a logical choice.
+/// However, on some architecture and compiler combinations, a bigger type
+/// may give better speed, because the probability variables are accessed
+/// a lot. On the other hand, bigger probability type increases cache
+/// footprint, since there are 2 to 14 thousand probability variables in
+/// LZMA (assuming the limit of lc + lp <= 4; with lc + lp <= 12 there
+/// would be about 1.5 million variables).
+///
+/// With malicious files, the initialization speed of the LZMA decoder can
+/// become important. In that case, smaller probability variables mean that
+/// there is less bytes to write to RAM, which makes initialization faster.
+/// With big probability type, the initialization can become so slow that it
+/// can be a problem e.g. for email servers doing virus scanning.
+///
+/// I will be sticking to uint16_t unless some specific architectures
+/// are *much* faster (20-50 %) with uint32_t.
+typedef uint16_t probability;
+
+#endif
Property changes on: xz/src/liblzma/rangecoder/range_common.h
___________________________________________________________________
Added: svn:eol-style
+ LF
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