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3b34851de1
broken. API has changed a lot and it will still change a little more here and there. The command line tool doesn't have all the required changes to reflect the API changes, so it's easy to get "internal error" or trigger assertions.
81 lines
2.7 KiB
C
81 lines
2.7 KiB
C
///////////////////////////////////////////////////////////////////////////////
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//
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/// \file range_common.h
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/// \brief Common things for range encoder and decoder
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//
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// Copyright (C) 1999-2006 Igor Pavlov
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// Copyright (C) 2006 Lasse Collin
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Lesser General Public
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// License as published by the Free Software Foundation; either
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// version 2.1 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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///////////////////////////////////////////////////////////////////////////////
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#ifndef LZMA_RANGE_COMMON_H
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#define LZMA_RANGE_COMMON_H
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#ifdef HAVE_CONFIG_H
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# include "common.h"
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#endif
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///////////////
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// Constants //
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///////////////
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#define RC_SHIFT_BITS 8
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#define RC_TOP_BITS 24
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#define RC_TOP_VALUE (UINT32_C(1) << RC_TOP_BITS)
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#define RC_BIT_MODEL_TOTAL_BITS 11
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#define RC_BIT_MODEL_TOTAL (UINT32_C(1) << RC_BIT_MODEL_TOTAL_BITS)
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#define RC_MOVE_BITS 5
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////////////
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// Macros //
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////////////
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// Resets the probability so that both 0 and 1 have probability of 50 %
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#define bit_reset(prob) \
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prob = RC_BIT_MODEL_TOTAL >> 1
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// This does the same for a complete bit tree.
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// (A tree represented as an array.)
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#define bittree_reset(probs, bit_levels) \
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for (uint32_t bt_i = 0; bt_i < (1 << (bit_levels)); ++bt_i) \
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bit_reset((probs)[bt_i])
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//////////////////////
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// Type definitions //
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//////////////////////
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/// \brief Type of probabilities used with range coder
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///
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/// This needs to be at least 12-bit integer, so uint16_t is a logical choice.
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/// However, on some architecture and compiler combinations, a bigger type
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/// may give better speed, because the probability variables are accessed
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/// a lot. On the other hand, bigger probability type increases cache
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/// footprint, since there are 2 to 14 thousand probability variables in
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/// LZMA (assuming the limit of lc + lp <= 4; with lc + lp <= 12 there
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/// would be about 1.5 million variables).
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///
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/// With malicious files, the initialization speed of the LZMA decoder can
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/// become important. In that case, smaller probability variables mean that
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/// there is less bytes to write to RAM, which makes initialization faster.
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/// With big probability type, the initialization can become so slow that it
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/// can be a problem e.g. for email servers doing virus scanning.
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///
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/// I will be sticking to uint16_t unless some specific architectures
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/// are *much* faster (20-50 %) with uint32_t.
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typedef uint16_t probability;
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#endif
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