| 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
|
|
|
|
|