/*
   * 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