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 /*
  * 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

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