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224 lines
6.8 KiB
224 lines
6.8 KiB
/////////////////////////////////////////////////////////////////////////////// |
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// |
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/// \file lzma_common.h |
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/// \brief Private definitions common to LZMA encoder and decoder |
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/// |
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// Authors: Igor Pavlov |
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// Lasse Collin |
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// |
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// This file has been put into the public domain. |
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// You can do whatever you want with this file. |
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// |
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/////////////////////////////////////////////////////////////////////////////// |
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#ifndef LZMA_LZMA_COMMON_H |
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#define LZMA_LZMA_COMMON_H |
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#include "common.h" |
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#include "range_common.h" |
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/////////////////// |
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// Miscellaneous // |
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/////////////////// |
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/// Maximum number of position states. A position state is the lowest pos bits |
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/// number of bits of the current uncompressed offset. In some places there |
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/// are different sets of probabilities for different pos states. |
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#define POS_STATES_MAX (1 << LZMA_PB_MAX) |
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/// Validates lc, lp, and pb. |
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static inline bool |
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is_lclppb_valid(const lzma_options_lzma *options) |
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{ |
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return options->lc <= LZMA_LCLP_MAX && options->lp <= LZMA_LCLP_MAX |
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&& options->lc + options->lp <= LZMA_LCLP_MAX |
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&& options->pb <= LZMA_PB_MAX; |
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} |
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/////////// |
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// State // |
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/////////// |
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/// This enum is used to track which events have occurred most recently and |
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/// in which order. This information is used to predict the next event. |
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/// |
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/// Events: |
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/// - Literal: One 8-bit byte |
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/// - Match: Repeat a chunk of data at some distance |
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/// - Long repeat: Multi-byte match at a recently seen distance |
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/// - Short repeat: One-byte repeat at a recently seen distance |
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/// |
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/// The event names are in from STATE_oldest_older_previous. REP means |
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/// either short or long repeated match, and NONLIT means any non-literal. |
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typedef enum { |
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STATE_LIT_LIT, |
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STATE_MATCH_LIT_LIT, |
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STATE_REP_LIT_LIT, |
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STATE_SHORTREP_LIT_LIT, |
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STATE_MATCH_LIT, |
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STATE_REP_LIT, |
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STATE_SHORTREP_LIT, |
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STATE_LIT_MATCH, |
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STATE_LIT_LONGREP, |
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STATE_LIT_SHORTREP, |
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STATE_NONLIT_MATCH, |
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STATE_NONLIT_REP, |
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} lzma_lzma_state; |
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/// Total number of states |
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#define STATES 12 |
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/// The lowest 7 states indicate that the previous state was a literal. |
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#define LIT_STATES 7 |
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/// Indicate that the latest state was a literal. |
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#define update_literal(state) \ |
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state = ((state) <= STATE_SHORTREP_LIT_LIT \ |
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? STATE_LIT_LIT \ |
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: ((state) <= STATE_LIT_SHORTREP \ |
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? (state) - 3 \ |
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: (state) - 6)) |
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/// Indicate that the latest state was a match. |
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#define update_match(state) \ |
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state = ((state) < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH) |
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/// Indicate that the latest state was a long repeated match. |
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#define update_long_rep(state) \ |
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state = ((state) < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP) |
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/// Indicate that the latest state was a short match. |
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#define update_short_rep(state) \ |
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state = ((state) < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP) |
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/// Test if the previous state was a literal. |
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#define is_literal_state(state) \ |
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((state) < LIT_STATES) |
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///////////// |
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// Literal // |
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///////////// |
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/// Each literal coder is divided in three sections: |
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/// - 0x001-0x0FF: Without match byte |
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/// - 0x101-0x1FF: With match byte; match bit is 0 |
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/// - 0x201-0x2FF: With match byte; match bit is 1 |
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/// |
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/// Match byte is used when the previous LZMA symbol was something else than |
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/// a literal (that is, it was some kind of match). |
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#define LITERAL_CODER_SIZE 0x300 |
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/// Maximum number of literal coders |
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#define LITERAL_CODERS_MAX (1 << LZMA_LCLP_MAX) |
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/// Locate the literal coder for the next literal byte. The choice depends on |
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/// - the lowest literal_pos_bits bits of the position of the current |
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/// byte; and |
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/// - the highest literal_context_bits bits of the previous byte. |
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#define literal_subcoder(probs, lc, lp_mask, pos, prev_byte) \ |
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((probs)[(((pos) & lp_mask) << lc) + ((prev_byte) >> (8 - lc))]) |
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static inline void |
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literal_init(probability (*probs)[LITERAL_CODER_SIZE], |
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uint32_t lc, uint32_t lp) |
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{ |
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assert(lc + lp <= LZMA_LCLP_MAX); |
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const uint32_t coders = 1U << (lc + lp); |
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for (uint32_t i = 0; i < coders; ++i) |
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for (uint32_t j = 0; j < LITERAL_CODER_SIZE; ++j) |
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bit_reset(probs[i][j]); |
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return; |
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} |
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////////////////// |
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// Match length // |
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////////////////// |
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// Minimum length of a match is two bytes. |
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#define MATCH_LEN_MIN 2 |
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// Match length is encoded with 4, 5, or 10 bits. |
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// |
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// Length Bits |
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// 2-9 4 = Choice=0 + 3 bits |
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// 10-17 5 = Choice=1 + Choice2=0 + 3 bits |
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// 18-273 10 = Choice=1 + Choice2=1 + 8 bits |
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#define LEN_LOW_BITS 3 |
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#define LEN_LOW_SYMBOLS (1 << LEN_LOW_BITS) |
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#define LEN_MID_BITS 3 |
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#define LEN_MID_SYMBOLS (1 << LEN_MID_BITS) |
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#define LEN_HIGH_BITS 8 |
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#define LEN_HIGH_SYMBOLS (1 << LEN_HIGH_BITS) |
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#define LEN_SYMBOLS (LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS + LEN_HIGH_SYMBOLS) |
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// Maximum length of a match is 273 which is a result of the encoding |
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// described above. |
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#define MATCH_LEN_MAX (MATCH_LEN_MIN + LEN_SYMBOLS - 1) |
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//////////////////// |
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// Match distance // |
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//////////////////// |
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// Different sets of probabilities are used for match distances that have very |
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// short match length: Lengths of 2, 3, and 4 bytes have a separate set of |
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// probabilities for each length. The matches with longer length use a shared |
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// set of probabilities. |
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#define DIST_STATES 4 |
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// Macro to get the index of the appropriate probability array. |
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#define get_dist_state(len) \ |
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((len) < DIST_STATES + MATCH_LEN_MIN \ |
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? (len) - MATCH_LEN_MIN \ |
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: DIST_STATES - 1) |
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// The highest two bits of a match distance (distance slot) are encoded |
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// using six bits. See fastpos.h for more explanation. |
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#define DIST_SLOT_BITS 6 |
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#define DIST_SLOTS (1 << DIST_SLOT_BITS) |
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// Match distances up to 127 are fully encoded using probabilities. Since |
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// the highest two bits (distance slot) are always encoded using six bits, |
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// the distances 0-3 don't need any additional bits to encode, since the |
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// distance slot itself is the same as the actual distance. DIST_MODEL_START |
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// indicates the first distance slot where at least one additional bit is |
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// needed. |
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#define DIST_MODEL_START 4 |
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// Match distances greater than 127 are encoded in three pieces: |
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// - distance slot: the highest two bits |
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// - direct bits: 2-26 bits below the highest two bits |
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// - alignment bits: four lowest bits |
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// |
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// Direct bits don't use any probabilities. |
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// |
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// The distance slot value of 14 is for distances 128-191 (see the table in |
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// fastpos.h to understand why). |
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#define DIST_MODEL_END 14 |
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// Distance slots that indicate a distance <= 127. |
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#define FULL_DISTANCES_BITS (DIST_MODEL_END / 2) |
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#define FULL_DISTANCES (1 << FULL_DISTANCES_BITS) |
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// For match distances greater than 127, only the highest two bits and the |
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// lowest four bits (alignment) is encoded using probabilities. |
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#define ALIGN_BITS 4 |
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#define ALIGN_SIZE (1 << ALIGN_BITS) |
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#define ALIGN_MASK (ALIGN_SIZE - 1) |
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// LZMA remembers the four most recent match distances. Reusing these distances |
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// tends to take less space than re-encoding the actual distance value. |
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#define REPS 4 |
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#endif
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