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xz_lzma2.h (6112B)

---

/*
* LZMA2 definitions
*
* Authors: Lasse Collin <lasse.collin@tukaani.org>
*          Igor Pavlov <http://7-zip.org/>
*
* This file has been put into the public domain.
* You can do whatever you want with this file.
*/

#ifndef XZ_LZMA2_H
#define XZ_LZMA2_H

/* Range coder constants */
#define RC_SHIFT_BITS 8
#define RC_TOP_BITS 24
#define RC_TOP_VALUE (1 << RC_TOP_BITS)
#define RC_BIT_MODEL_TOTAL_BITS 11
#define RC_BIT_MODEL_TOTAL (1 << RC_BIT_MODEL_TOTAL_BITS)
#define RC_MOVE_BITS 5

/*
* Maximum number of position states. A position state is the lowest pb
* number of bits of the current uncompressed offset. In some places there
* are different sets of probabilities for different position states.
*/
#define POS_STATES_MAX (1 << 4)

/*
* This enum is used to track which LZMA symbols have occurred most recently
* and in which order. This information is used to predict the next symbol.
*
* Symbols:
*  - Literal: One 8-bit byte
*  - Match: Repeat a chunk of data at some distance
*  - Long repeat: Multi-byte match at a recently seen distance
*  - Short repeat: One-byte repeat at a recently seen distance
*
* The symbol names are in from STATE_oldest_older_previous. REP means
* either short or long repeated match, and NONLIT means any non-literal.
*/
enum lzma_state {
STATE_LIT_LIT,
STATE_MATCH_LIT_LIT,
STATE_REP_LIT_LIT,
STATE_SHORTREP_LIT_LIT,
STATE_MATCH_LIT,
STATE_REP_LIT,
STATE_SHORTREP_LIT,
STATE_LIT_MATCH,
STATE_LIT_LONGREP,
STATE_LIT_SHORTREP,
STATE_NONLIT_MATCH,
STATE_NONLIT_REP
};

/* Total number of states */
#define STATES 12

/* The lowest 7 states indicate that the previous state was a literal. */
#define LIT_STATES 7

/* Indicate that the latest symbol was a literal. */
static inline void lzma_state_literal(enum lzma_state *state)
{
if (*state <= STATE_SHORTREP_LIT_LIT)
	*state = STATE_LIT_LIT;
else if (*state <= STATE_LIT_SHORTREP)
	*state -= 3;
else
	*state -= 6;
}

/* Indicate that the latest symbol was a match. */
static inline void lzma_state_match(enum lzma_state *state)
{
*state = *state < LIT_STATES ? STATE_LIT_MATCH : STATE_NONLIT_MATCH;
}

/* Indicate that the latest state was a long repeated match. */
static inline void lzma_state_long_rep(enum lzma_state *state)
{
*state = *state < LIT_STATES ? STATE_LIT_LONGREP : STATE_NONLIT_REP;
}

/* Indicate that the latest symbol was a short match. */
static inline void lzma_state_short_rep(enum lzma_state *state)
{
*state = *state < LIT_STATES ? STATE_LIT_SHORTREP : STATE_NONLIT_REP;
}

/* Test if the previous symbol was a literal. */
static inline bool lzma_state_is_literal(enum lzma_state state)
{
return state < LIT_STATES;
}

/* Each literal coder is divided in three sections:
*   - 0x001-0x0FF: Without match byte
*   - 0x101-0x1FF: With match byte; match bit is 0
*   - 0x201-0x2FF: With match byte; match bit is 1
*
* Match byte is used when the previous LZMA symbol was something else than
* a literal (that is, it was some kind of match).
*/
#define LITERAL_CODER_SIZE 0x300

/* Maximum number of literal coders */
#define LITERAL_CODERS_MAX (1 << 4)

/* Minimum length of a match is two bytes. */
#define MATCH_LEN_MIN 2

/* Match length is encoded with 4, 5, or 10 bits.
*
* Length   Bits
*  2-9      4 = Choice=0 + 3 bits
* 10-17     5 = Choice=1 + Choice2=0 + 3 bits
* 18-273   10 = Choice=1 + Choice2=1 + 8 bits
*/
#define LEN_LOW_BITS 3
#define LEN_LOW_SYMBOLS (1 << LEN_LOW_BITS)
#define LEN_MID_BITS 3
#define LEN_MID_SYMBOLS (1 << LEN_MID_BITS)
#define LEN_HIGH_BITS 8
#define LEN_HIGH_SYMBOLS (1 << LEN_HIGH_BITS)
#define LEN_SYMBOLS (LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS + LEN_HIGH_SYMBOLS)

/*
* Maximum length of a match is 273 which is a result of the encoding
* described above.
*/
#define MATCH_LEN_MAX (MATCH_LEN_MIN + LEN_SYMBOLS - 1)

/*
* Different sets of probabilities are used for match distances that have
* very short match length: Lengths of 2, 3, and 4 bytes have a separate
* set of probabilities for each length. The matches with longer length
* use a shared set of probabilities.
*/
#define DIST_STATES 4

/*
* Get the index of the appropriate probability array for decoding
* the distance slot.
*/
static inline uint32_t lzma_get_dist_state(uint32_t len)
{
return len < DIST_STATES + MATCH_LEN_MIN
		? len - MATCH_LEN_MIN : DIST_STATES - 1;
}

/*
* The highest two bits of a 32-bit match distance are encoded using six bits.
* This six-bit value is called a distance slot. This way encoding a 32-bit
* value takes 6-36 bits, larger values taking more bits.
*/
#define DIST_SLOT_BITS 6
#define DIST_SLOTS (1 << DIST_SLOT_BITS)

/* Match distances up to 127 are fully encoded using probabilities. Since
* the highest two bits (distance slot) are always encoded using six bits,
* the distances 0-3 don't need any additional bits to encode, since the
* distance slot itself is the same as the actual distance. DIST_MODEL_START
* indicates the first distance slot where at least one additional bit is
* needed.
*/
#define DIST_MODEL_START 4

/*
* Match distances greater than 127 are encoded in three pieces:
*   - distance slot: the highest two bits
*   - direct bits: 2-26 bits below the highest two bits
*   - alignment bits: four lowest bits
*
* Direct bits don't use any probabilities.
*
* The distance slot value of 14 is for distances 128-191.
*/
#define DIST_MODEL_END 14

/* Distance slots that indicate a distance <= 127. */
#define FULL_DISTANCES_BITS (DIST_MODEL_END / 2)
#define FULL_DISTANCES (1 << FULL_DISTANCES_BITS)

/*
* For match distances greater than 127, only the highest two bits and the
* lowest four bits (alignment) is encoded using probabilities.
*/
#define ALIGN_BITS 4
#define ALIGN_SIZE (1 << ALIGN_BITS)
#define ALIGN_MASK (ALIGN_SIZE - 1)

/* Total number of all probability variables */
#define PROBS_TOTAL (1846 + LITERAL_CODERS_MAX * LITERAL_CODER_SIZE)

/*
* LZMA remembers the four most recent match distances. Reusing these
* distances tends to take less space than re-encoding the actual
* distance value.
*/
#define REPS 4

#endif