227 lines
6.8 KiB
C
227 lines
6.8 KiB
C
///////////////////////////////////////////////////////////////////////////////
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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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uint32_t coders;
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uint32_t i, j;
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assert(lc + lp <= LZMA_LCLP_MAX);
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coders = 1U << (lc + lp);
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for (i = 0; i < coders; ++i)
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for (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 set of probabilities is 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 LEN_TO_POS_STATES 4
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// Macro to get the index of the appropriate probability array.
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#define get_len_to_pos_state(len) \
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((len) < LEN_TO_POS_STATES + MATCH_LEN_MIN \
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? (len) - MATCH_LEN_MIN \
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: LEN_TO_POS_STATES - 1)
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// The highest two bits of a match distance (pos slot) are encoded using six
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// bits. See fastpos.h for more explanation.
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#define POS_SLOT_BITS 6
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#define POS_SLOTS (1 << POS_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 (pos slot) are always encoded using six bits, the
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// distances 0-3 don't need any additional bits to encode, since the pos
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// slot itself is the same as the actual distance. START_POS_MODEL_INDEX
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// indicates the first pos slot where at least one additional bit is needed.
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#define START_POS_MODEL_INDEX 4
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// Match distances greater than 127 are encoded in three pieces:
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// - pos 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 pos 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 END_POS_MODEL_INDEX 14
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// Pos slots that indicate a distance <= 127.
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#define FULL_DISTANCES_BITS (END_POS_MODEL_INDEX / 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_TABLE_SIZE (1 << ALIGN_BITS)
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#define ALIGN_MASK (ALIGN_TABLE_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 REP_DISTANCES 4
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#endif
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