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 /*
  * LZMA2 decoder
  *
  * 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.
  */
 
 #include "xz_private.h"
 #include "xz_lzma2.h"
 
 /*
  * Range decoder initialization eats the first five bytes of each LZMA chunk.
  */
 #define RC_INIT_BYTES 5
 
 /*
  * Minimum number of usable input buffer to safely decode one LZMA symbol.
  * The worst case is that we decode 22 bits using probabilities and 26
  * direct bits. This may decode at maximum of 20 bytes of input. However,
  * lzma_main() does an extra normalization before returning, thus we
  * need to put 21 here.
  */
 #define LZMA_IN_REQUIRED 21
 
 /*
  * Dictionary (history buffer)
  *
  * These are always true:
  *    start <= pos <= full <= end
  *    pos <= limit <= end
  *
  * In multi-call mode, also these are true:
  *    end == size
  *    size <= size_max
  *    allocated <= size
  *
  * Most of these variables are size_t to support single-call mode,
  * in which the dictionary variables address the actual output
  * buffer directly.
  */
 struct dictionary {
     /* Beginning of the history buffer */
     uint8_t *buf;
 
     /* Old position in buf (before decoding more data) */
     size_t start;
 
     /* Position in buf */
     size_t pos;
 
     /*
      * How full dictionary is. This is used to detect corrupt input that
      * would read beyond the beginning of the uncompressed stream.
      */
     size_t full;
 
     /* Write limit; we don't write to buf[limit] or later bytes. */
     size_t limit;
 
     /*
      * End of the dictionary buffer. In multi-call mode, this is
      * the same as the dictionary size. In single-call mode, this
      * indicates the size of the output buffer.
      */
     size_t end;
 
     /*
      * Size of the dictionary as specified in Block Header. This is used
      * together with "full" to detect corrupt input that would make us
      * read beyond the beginning of the uncompressed stream.
      */
     uint32_t size;
 
     /*
      * Maximum allowed dictionary size in multi-call mode.
      * This is ignored in single-call mode.
      */
     uint32_t size_max;
 
     /*
      * Amount of memory currently allocated for the dictionary.
      * This is used only with XZ_DYNALLOC. (With XZ_PREALLOC,
      * size_max is always the same as the allocated size.)
      */
     uint32_t allocated;
 
     /* Operation mode */
     enum xz_mode mode;
 };
 
 /* Range decoder */
 struct rc_dec {
     uint32_t range;
     uint32_t code;
 
     /*
      * Number of initializing bytes remaining to be read
      * by rc_read_init().
      */
     uint32_t init_bytes_left;
 
     /*
      * Buffer from which we read our input. It can be either
      * temp.buf or the caller-provided input buffer.
      */
     const uint8_t *in;
     size_t in_pos;
     size_t in_limit;
 };
 
 /* Probabilities for a length decoder. */
 struct lzma_len_dec {
     /* Probability of match length being at least 10 */
     uint16_t choice;
 
     /* Probability of match length being at least 18 */
     uint16_t choice2;
 
     /* Probabilities for match lengths 2-9 */
     uint16_t low[POS_STATES_MAX][LEN_LOW_SYMBOLS];
 
     /* Probabilities for match lengths 10-17 */
     uint16_t mid[POS_STATES_MAX][LEN_MID_SYMBOLS];
 
     /* Probabilities for match lengths 18-273 */
     uint16_t high[LEN_HIGH_SYMBOLS];
 };
 
 struct lzma_dec {
     /* Distances of latest four matches */
     uint32_t rep0;
     uint32_t rep1;
     uint32_t rep2;
     uint32_t rep3;
 
     /* Types of the most recently seen LZMA symbols */
     enum lzma_state state;
 
     /*
      * Length of a match. This is updated so that dict_repeat can
      * be called again to finish repeating the whole match.
      */
     uint32_t len;
 
     /*
      * LZMA properties or related bit masks (number of literal
      * context bits, a mask dervied from the number of literal
      * position bits, and a mask dervied from the number
      * position bits)
      */
     uint32_t lc;
     uint32_t literal_pos_mask; /* (1 << lp) - 1 */
     uint32_t pos_mask;         /* (1 << pb) - 1 */
 
     /* If 1, it's a match. Otherwise it's a single 8-bit literal. */
     uint16_t is_match[STATES][POS_STATES_MAX];
 
     /* If 1, it's a repeated match. The distance is one of rep0 .. rep3. */
     uint16_t is_rep[STATES];
 
     /*
      * If 0, distance of a repeated match is rep0.
      * Otherwise check is_rep1.
      */
     uint16_t is_rep0[STATES];
 
     /*
      * If 0, distance of a repeated match is rep1.
      * Otherwise check is_rep2.
      */
     uint16_t is_rep1[STATES];
 
     /* If 0, distance of a repeated match is rep2. Otherwise it is rep3. */
     uint16_t is_rep2[STATES];
 
     /*
      * If 1, the repeated match has length of one byte. Otherwise
      * the length is decoded from rep_len_decoder.
      */
     uint16_t is_rep0_long[STATES][POS_STATES_MAX];
 
     /*
      * Probability tree for the highest two bits of the match
      * distance. There is a separate probability tree for match
      * lengths of 2 (i.e. MATCH_LEN_MIN), 3, 4, and [5, 273].
      */
     uint16_t dist_slot[DIST_STATES][DIST_SLOTS];
 
     /*
      * Probility trees for additional bits for match distance
      * when the distance is in the range [4, 127].
      */
     uint16_t dist_special[FULL_DISTANCES - DIST_MODEL_END];
 
     /*
      * Probability tree for the lowest four bits of a match
      * distance that is equal to or greater than 128.
      */
     uint16_t dist_align[ALIGN_SIZE];
 
     /* Length of a normal match */
     struct lzma_len_dec match_len_dec;
 
     /* Length of a repeated match */
     struct lzma_len_dec rep_len_dec;
 
     /* Probabilities of literals */
     uint16_t literal[LITERAL_CODERS_MAX][LITERAL_CODER_SIZE];
 };
 
 struct lzma2_dec {
     /* Position in xz_dec_lzma2_run(). */
     enum lzma2_seq {
         SEQ_CONTROL,
         SEQ_UNCOMPRESSED_1,
         SEQ_UNCOMPRESSED_2,
         SEQ_COMPRESSED_0,
         SEQ_COMPRESSED_1,
         SEQ_PROPERTIES,
         SEQ_LZMA_PREPARE,
         SEQ_LZMA_RUN,
         SEQ_COPY
     } sequence;
 
     /* Next position after decoding the compressed size of the chunk. */
     enum lzma2_seq next_sequence;
 
     /* Uncompressed size of LZMA chunk (2 MiB at maximum) */
     uint32_t uncompressed;
 
     /*
      * Compressed size of LZMA chunk or compressed/uncompressed
      * size of uncompressed chunk (64 KiB at maximum)
      */
     uint32_t compressed;
 
     /*
      * True if dictionary reset is needed. This is false before
      * the first chunk (LZMA or uncompressed).
      */
     bool need_dict_reset;
 
     /*
      * True if new LZMA properties are needed. This is false
      * before the first LZMA chunk.
      */
     bool need_props;
 };
 
 struct xz_dec_lzma2 {
     /*
      * The order below is important on x86 to reduce code size and
      * it shouldn't hurt on other platforms. Everything up to and
      * including lzma.pos_mask are in the first 128 bytes on x86-32,
      * which allows using smaller instructions to access those
      * variables. On x86-64, fewer variables fit into the first 128
      * bytes, but this is still the best order without sacrificing
      * the readability by splitting the structures.
      */
     struct rc_dec rc;
     struct dictionary dict;
     struct lzma2_dec lzma2;
     struct lzma_dec lzma;
 
     /*
      * Temporary buffer which holds small number of input bytes between
      * decoder calls. See lzma2_lzma() for details.
      */
     struct {
         uint32_t size;
         uint8_t buf[3 * LZMA_IN_REQUIRED];
     } temp;
 };
 
 /**************
  * Dictionary *
  **************/
 
 /*
  * Reset the dictionary state. When in single-call mode, set up the beginning
  * of the dictionary to point to the actual output buffer.
  */
 static void dict_reset(struct dictionary *dict, struct xz_buf *b)
 {
     if (DEC_IS_SINGLE(dict->mode)) {
         dict->buf = b->out + b->out_pos;
         dict->end = b->out_size - b->out_pos;
     }
 
     dict->start = 0;
     dict->pos = 0;
     dict->limit = 0;
     dict->full = 0;
 }
 
 /* Set dictionary write limit */
 static void dict_limit(struct dictionary *dict, size_t out_max)
 {
     if (dict->end - dict->pos <= out_max)
         dict->limit = dict->end;
     else
         dict->limit = dict->pos + out_max;
 }
 
 /* Return true if at least one byte can be written into the dictionary. */
 static inline bool dict_has_space(const struct dictionary *dict)
 {
     return dict->pos < dict->limit;
 }
 
 /*
  * Get a byte from the dictionary at the given distance. The distance is
  * assumed to valid, or as a special case, zero when the dictionary is
  * still empty. This special case is needed for single-call decoding to
  * avoid writing a '\0' to the end of the destination buffer.
  */
 static inline uint32_t dict_get(const struct dictionary *dict, uint32_t dist)
 {
     size_t offset = dict->pos - dist - 1;
 
     if (dist >= dict->pos)
         offset += dict->end;
 
     return dict->full > 0 ? dict->buf[offset] : 0;
 }
 
 /*
  * Put one byte into the dictionary. It is assumed that there is space for it.
  */
 static inline void dict_put(struct dictionary *dict, uint8_t byte)
 {
     dict->buf[dict->pos++] = byte;
 
     if (dict->full < dict->pos)
         dict->full = dict->pos;
 }
 
 /*
  * Repeat given number of bytes from the given distance. If the distance is
  * invalid, false is returned. On success, true is returned and *len is
  * updated to indicate how many bytes were left to be repeated.
  */
 static bool dict_repeat(struct dictionary *dict, uint32_t *len, uint32_t dist)
 {
     size_t back;
     uint32_t left;
 
     if (dist >= dict->full || dist >= dict->size)
         return false;
 
     left = min_t(size_t, dict->limit - dict->pos, *len);
     *len -= left;
 
     back = dict->pos - dist - 1;
     if (dist >= dict->pos)
         back += dict->end;
 
     do {
         dict->buf[dict->pos++] = dict->buf[back++];
         if (back == dict->end)
             back = 0;
     } while (--left > 0);
 
     if (dict->full < dict->pos)
         dict->full = dict->pos;
 
     return true;
 }
 
 /* Copy uncompressed data as is from input to dictionary and output buffers. */
 static void dict_uncompressed(struct dictionary *dict, struct xz_buf *b,
                   uint32_t *left)
 {
     size_t copy_size;
 
     while (*left > 0 && b->in_pos < b->in_size
             && b->out_pos < b->out_size) {
         copy_size = min(b->in_size - b->in_pos,
                 b->out_size - b->out_pos);
         if (copy_size > dict->end - dict->pos)
             copy_size = dict->end - dict->pos;
         if (copy_size > *left)
             copy_size = *left;
 
         *left -= copy_size;
 
         memcpy(dict->buf + dict->pos, b->in + b->in_pos, copy_size);
         dict->pos += copy_size;
 
         if (dict->full < dict->pos)
             dict->full = dict->pos;
 
         if (DEC_IS_MULTI(dict->mode)) {
             if (dict->pos == dict->end)
                 dict->pos = 0;
 
             memcpy(b->out + b->out_pos, b->in + b->in_pos,
                     copy_size);
         }
 
         dict->start = dict->pos;
 
         b->out_pos += copy_size;
         b->in_pos += copy_size;
     }
 }
 
 /*
  * Flush pending data from dictionary to b->out. It is assumed that there is
  * enough space in b->out. This is guaranteed because caller uses dict_limit()
  * before decoding data into the dictionary.
  */
 static uint32_t dict_flush(struct dictionary *dict, struct xz_buf *b)
 {
     size_t copy_size = dict->pos - dict->start;
 
     if (DEC_IS_MULTI(dict->mode)) {
         if (dict->pos == dict->end)
             dict->pos = 0;
 
         memcpy(b->out + b->out_pos, dict->buf + dict->start,
                 copy_size);
     }
 
     dict->start = dict->pos;
     b->out_pos += copy_size;
     return copy_size;
 }
 
 /*****************
  * Range decoder *
  *****************/
 
 /* Reset the range decoder. */
 static void rc_reset(struct rc_dec *rc)
 {
     rc->range = (uint32_t)-1;
     rc->code = 0;
     rc->init_bytes_left = RC_INIT_BYTES;
 }
 
 /*
  * Read the first five initial bytes into rc->code if they haven't been
  * read already. (Yes, the first byte gets completely ignored.)
  */
 static bool rc_read_init(struct rc_dec *rc, struct xz_buf *b)
 {
     while (rc->init_bytes_left > 0) {
         if (b->in_pos == b->in_size)
             return false;
 
         rc->code = (rc->code << 8) + b->in[b->in_pos++];
         --rc->init_bytes_left;
     }
 
     return true;
 }
 
 /* Return true if there may not be enough input for the next decoding loop. */
 static inline bool rc_limit_exceeded(const struct rc_dec *rc)
 {
     return rc->in_pos > rc->in_limit;
 }
 
 /*
  * Return true if it is possible (from point of view of range decoder) that
  * we have reached the end of the LZMA chunk.
  */
 static inline bool rc_is_finished(const struct rc_dec *rc)
 {
     return rc->code == 0;
 }
 
 #ifdef __rtems__
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wattributes"
 #endif /* __rtems__ */
 /* Read the next input byte if needed. */
 static __always_inline void rc_normalize(struct rc_dec *rc)
 {
     if (rc->range < RC_TOP_VALUE) {
         rc->range <<= RC_SHIFT_BITS;
         rc->code = (rc->code << RC_SHIFT_BITS) + rc->in[rc->in_pos++];
     }
 }
 
 /*
  * Decode one bit. In some versions, this function has been splitted in three
  * functions so that the compiler is supposed to be able to more easily avoid
  * an extra branch. In this particular version of the LZMA decoder, this
  * doesn't seem to be a good idea (tested with GCC 3.3.6, 3.4.6, and 4.3.3
  * on x86). Using a non-splitted version results in nicer looking code too.
  *
  * NOTE: This must return an int. Do not make it return a bool or the speed
  * of the code generated by GCC 3.x decreases 10-15 %. (GCC 4.3 doesn't care,
  * and it generates 10-20 % faster code than GCC 3.x from this file anyway.)
  */
 static __always_inline int rc_bit(struct rc_dec *rc, uint16_t *prob)
 {
     uint32_t bound;
     int bit;
 
     rc_normalize(rc);
     bound = (rc->range >> RC_BIT_MODEL_TOTAL_BITS) * *prob;
     if (rc->code < bound) {
         rc->range = bound;
         *prob += (RC_BIT_MODEL_TOTAL - *prob) >> RC_MOVE_BITS;
         bit = 0;
     } else {
         rc->range -= bound;
         rc->code -= bound;
         *prob -= *prob >> RC_MOVE_BITS;
         bit = 1;
     }
 
     return bit;
 }
 
 /* Decode a bittree starting from the most significant bit. */
 static __always_inline uint32_t rc_bittree(struct rc_dec *rc,
                        uint16_t *probs, uint32_t limit)
 {
     uint32_t symbol = 1;
 
     do {
         if (rc_bit(rc, &probs[symbol]))
             symbol = (symbol << 1) + 1;
         else
             symbol <<= 1;
     } while (symbol < limit);
 
     return symbol;
 }
 
 /* Decode a bittree starting from the least significant bit. */
 static __always_inline void rc_bittree_reverse(struct rc_dec *rc,
                            uint16_t *probs,
                            uint32_t *dest, uint32_t limit)
 {
     uint32_t symbol = 1;
     uint32_t i = 0;
 
     do {
         if (rc_bit(rc, &probs[symbol])) {
             symbol = (symbol << 1) + 1;
             *dest += 1 << i;
         } else {
             symbol <<= 1;
         }
     } while (++i < limit);
 }
 #ifdef __rtems__
 #pragma GCC diagnostic pop
 #endif /* __rtems__ */
 
 /* Decode direct bits (fixed fifty-fifty probability) */
 static inline void rc_direct(struct rc_dec *rc, uint32_t *dest, uint32_t limit)
 {
     uint32_t mask;
 
     do {
         rc_normalize(rc);
         rc->range >>= 1;
         rc->code -= rc->range;
         mask = (uint32_t)0 - (rc->code >> 31);
         rc->code += rc->range & mask;
         *dest = (*dest << 1) + (mask + 1);
     } while (--limit > 0);
 }
 
 /********
  * LZMA *
  ********/
 
 /* Get pointer to literal coder probability array. */
 static uint16_t *lzma_literal_probs(struct xz_dec_lzma2 *s)
 {
     uint32_t prev_byte = dict_get(&s->dict, 0);
     uint32_t low = prev_byte >> (8 - s->lzma.lc);
     uint32_t high = (s->dict.pos & s->lzma.literal_pos_mask) << s->lzma.lc;
     return s->lzma.literal[low + high];
 }
 
 /* Decode a literal (one 8-bit byte) */
 static void lzma_literal(struct xz_dec_lzma2 *s)
 {
     uint16_t *probs;
     uint32_t symbol;
     uint32_t match_byte;
     uint32_t match_bit;
     uint32_t offset;
     uint32_t i;
 
     probs = lzma_literal_probs(s);
 
     if (lzma_state_is_literal(s->lzma.state)) {
         symbol = rc_bittree(&s->rc, probs, 0x100);
     } else {
         symbol = 1;
         match_byte = dict_get(&s->dict, s->lzma.rep0) << 1;
         offset = 0x100;
 
         do {
             match_bit = match_byte & offset;
             match_byte <<= 1;
             i = offset + match_bit + symbol;
 
             if (rc_bit(&s->rc, &probs[i])) {
                 symbol = (symbol << 1) + 1;
                 offset &= match_bit;
             } else {
                 symbol <<= 1;
                 offset &= ~match_bit;
             }
         } while (symbol < 0x100);
     }
 
     dict_put(&s->dict, (uint8_t)symbol);
     lzma_state_literal(&s->lzma.state);
 }
 
 /* Decode the length of the match into s->lzma.len. */
 static void lzma_len(struct xz_dec_lzma2 *s, struct lzma_len_dec *l,
              uint32_t pos_state)
 {
     uint16_t *probs;
     uint32_t limit;
 
     if (!rc_bit(&s->rc, &l->choice)) {
         probs = l->low[pos_state];
         limit = LEN_LOW_SYMBOLS;
         s->lzma.len = MATCH_LEN_MIN;
     } else {
         if (!rc_bit(&s->rc, &l->choice2)) {
             probs = l->mid[pos_state];
             limit = LEN_MID_SYMBOLS;
             s->lzma.len = MATCH_LEN_MIN + LEN_LOW_SYMBOLS;
         } else {
             probs = l->high;
             limit = LEN_HIGH_SYMBOLS;
             s->lzma.len = MATCH_LEN_MIN + LEN_LOW_SYMBOLS
                     + LEN_MID_SYMBOLS;
         }
     }
 
     s->lzma.len += rc_bittree(&s->rc, probs, limit) - limit;
 }
 
 /* Decode a match. The distance will be stored in s->lzma.rep0. */
 static void lzma_match(struct xz_dec_lzma2 *s, uint32_t pos_state)
 {
     uint16_t *probs;
     uint32_t dist_slot;
     uint32_t limit;
 
     lzma_state_match(&s->lzma.state);
 
     s->lzma.rep3 = s->lzma.rep2;
     s->lzma.rep2 = s->lzma.rep1;
     s->lzma.rep1 = s->lzma.rep0;
 
     lzma_len(s, &s->lzma.match_len_dec, pos_state);
 
     probs = s->lzma.dist_slot[lzma_get_dist_state(s->lzma.len)];
     dist_slot = rc_bittree(&s->rc, probs, DIST_SLOTS) - DIST_SLOTS;
 
     if (dist_slot < DIST_MODEL_START) {
         s->lzma.rep0 = dist_slot;
     } else {
         limit = (dist_slot >> 1) - 1;
         s->lzma.rep0 = 2 + (dist_slot & 1);
 
         if (dist_slot < DIST_MODEL_END) {
             s->lzma.rep0 <<= limit;
             probs = s->lzma.dist_special + s->lzma.rep0
                     - dist_slot - 1;
             rc_bittree_reverse(&s->rc, probs,
                     &s->lzma.rep0, limit);
         } else {
             rc_direct(&s->rc, &s->lzma.rep0, limit - ALIGN_BITS);
             s->lzma.rep0 <<= ALIGN_BITS;
             rc_bittree_reverse(&s->rc, s->lzma.dist_align,
                     &s->lzma.rep0, ALIGN_BITS);
         }
     }
 }
 
 /*
  * Decode a repeated match. The distance is one of the four most recently
  * seen matches. The distance will be stored in s->lzma.rep0.
  */
 static void lzma_rep_match(struct xz_dec_lzma2 *s, uint32_t pos_state)
 {
     uint32_t tmp;
 
     if (!rc_bit(&s->rc, &s->lzma.is_rep0[s->lzma.state])) {
         if (!rc_bit(&s->rc, &s->lzma.is_rep0_long[
                 s->lzma.state][pos_state])) {
             lzma_state_short_rep(&s->lzma.state);
             s->lzma.len = 1;
             return;
         }
     } else {
         if (!rc_bit(&s->rc, &s->lzma.is_rep1[s->lzma.state])) {
             tmp = s->lzma.rep1;
         } else {
             if (!rc_bit(&s->rc, &s->lzma.is_rep2[s->lzma.state])) {
                 tmp = s->lzma.rep2;
             } else {
                 tmp = s->lzma.rep3;
                 s->lzma.rep3 = s->lzma.rep2;
             }
 
             s->lzma.rep2 = s->lzma.rep1;
         }
 
         s->lzma.rep1 = s->lzma.rep0;
         s->lzma.rep0 = tmp;
     }
 
     lzma_state_long_rep(&s->lzma.state);
     lzma_len(s, &s->lzma.rep_len_dec, pos_state);
 }
 
 /* LZMA decoder core */
 static bool lzma_main(struct xz_dec_lzma2 *s)
 {
     uint32_t pos_state;
 
     /*
      * If the dictionary was reached during the previous call, try to
      * finish the possibly pending repeat in the dictionary.
      */
     if (dict_has_space(&s->dict) && s->lzma.len > 0)
         dict_repeat(&s->dict, &s->lzma.len, s->lzma.rep0);
 
     /*
      * Decode more LZMA symbols. One iteration may consume up to
      * LZMA_IN_REQUIRED - 1 bytes.
      */
     while (dict_has_space(&s->dict) && !rc_limit_exceeded(&s->rc)) {
         pos_state = s->dict.pos & s->lzma.pos_mask;
 
         if (!rc_bit(&s->rc, &s->lzma.is_match[
                 s->lzma.state][pos_state])) {
             lzma_literal(s);
         } else {
             if (rc_bit(&s->rc, &s->lzma.is_rep[s->lzma.state]))
                 lzma_rep_match(s, pos_state);
             else
                 lzma_match(s, pos_state);
 
             if (!dict_repeat(&s->dict, &s->lzma.len, s->lzma.rep0))
                 return false;
         }
     }
 
     /*
      * Having the range decoder always normalized when we are outside
      * this function makes it easier to correctly handle end of the chunk.
      */
     rc_normalize(&s->rc);
 
     return true;
 }
 
 /*
  * Reset the LZMA decoder and range decoder state. Dictionary is nore reset
  * here, because LZMA state may be reset without resetting the dictionary.
  */
 static void lzma_reset(struct xz_dec_lzma2 *s)
 {
     uint16_t *probs;
     size_t i;
 
     s->lzma.state = STATE_LIT_LIT;
     s->lzma.rep0 = 0;
     s->lzma.rep1 = 0;
     s->lzma.rep2 = 0;
     s->lzma.rep3 = 0;
 
     /*
      * All probabilities are initialized to the same value. This hack
      * makes the code smaller by avoiding a separate loop for each
      * probability array.
      *
      * This could be optimized so that only that part of literal
      * probabilities that are actually required. In the common case
      * we would write 12 KiB less.
      */
     probs = s->lzma.is_match[0];
     for (i = 0; i < PROBS_TOTAL; ++i)
         probs[i] = RC_BIT_MODEL_TOTAL / 2;
 
     rc_reset(&s->rc);
 }
 
 /*
  * Decode and validate LZMA properties (lc/lp/pb) and calculate the bit masks
  * from the decoded lp and pb values. On success, the LZMA decoder state is
  * reset and true is returned.
  */
 static bool lzma_props(struct xz_dec_lzma2 *s, uint8_t props)
 {
     if (props > (4 * 5 + 4) * 9 + 8)
         return false;
 
     s->lzma.pos_mask = 0;
     while (props >= 9 * 5) {
         props -= 9 * 5;
         ++s->lzma.pos_mask;
     }
 
     s->lzma.pos_mask = (1 << s->lzma.pos_mask) - 1;
 
     s->lzma.literal_pos_mask = 0;
     while (props >= 9) {
         props -= 9;
         ++s->lzma.literal_pos_mask;
     }
 
     s->lzma.lc = props;
 
     if (s->lzma.lc + s->lzma.literal_pos_mask > 4)
         return false;
 
     s->lzma.literal_pos_mask = (1 << s->lzma.literal_pos_mask) - 1;
 
     lzma_reset(s);
 
     return true;
 }
 
 /*********
  * LZMA2 *
  *********/
 
 /*
  * The LZMA decoder assumes that if the input limit (s->rc.in_limit) hasn't
  * been exceeded, it is safe to read up to LZMA_IN_REQUIRED bytes. This
  * wrapper function takes care of making the LZMA decoder's assumption safe.
  *
  * As long as there is plenty of input left to be decoded in the current LZMA
  * chunk, we decode directly from the caller-supplied input buffer until
  * there's LZMA_IN_REQUIRED bytes left. Those remaining bytes are copied into
  * s->temp.buf, which (hopefully) gets filled on the next call to this
  * function. We decode a few bytes from the temporary buffer so that we can
  * continue decoding from the caller-supplied input buffer again.
  */
 static bool lzma2_lzma(struct xz_dec_lzma2 *s, struct xz_buf *b)
 {
     size_t in_avail;
     uint32_t tmp;
 
     in_avail = b->in_size - b->in_pos;
     if (s->temp.size > 0 || s->lzma2.compressed == 0) {
         tmp = 2 * LZMA_IN_REQUIRED - s->temp.size;
         if (tmp > s->lzma2.compressed - s->temp.size)
             tmp = s->lzma2.compressed - s->temp.size;
         if (tmp > in_avail)
             tmp = in_avail;
 
         memcpy(s->temp.buf + s->temp.size, b->in + b->in_pos, tmp);
 
         if (s->temp.size + tmp == s->lzma2.compressed) {
             memzero(s->temp.buf + s->temp.size + tmp,
                     sizeof(s->temp.buf)
                         - s->temp.size - tmp);
             s->rc.in_limit = s->temp.size + tmp;
         } else if (s->temp.size + tmp < LZMA_IN_REQUIRED) {
             s->temp.size += tmp;
             b->in_pos += tmp;
             return true;
         } else {
             s->rc.in_limit = s->temp.size + tmp - LZMA_IN_REQUIRED;
         }
 
         s->rc.in = s->temp.buf;
         s->rc.in_pos = 0;
 
         if (!lzma_main(s) || s->rc.in_pos > s->temp.size + tmp)
             return false;
 
         s->lzma2.compressed -= s->rc.in_pos;
 
         if (s->rc.in_pos < s->temp.size) {
             s->temp.size -= s->rc.in_pos;
             memmove(s->temp.buf, s->temp.buf + s->rc.in_pos,
                     s->temp.size);
             return true;
         }
 
         b->in_pos += s->rc.in_pos - s->temp.size;
         s->temp.size = 0;
     }
 
     in_avail = b->in_size - b->in_pos;
     if (in_avail >= LZMA_IN_REQUIRED) {
         s->rc.in = b->in;
         s->rc.in_pos = b->in_pos;
 
         if (in_avail >= s->lzma2.compressed + LZMA_IN_REQUIRED)
             s->rc.in_limit = b->in_pos + s->lzma2.compressed;
         else
             s->rc.in_limit = b->in_size - LZMA_IN_REQUIRED;
 
         if (!lzma_main(s))
             return false;
 
         in_avail = s->rc.in_pos - b->in_pos;
         if (in_avail > s->lzma2.compressed)
             return false;
 
         s->lzma2.compressed -= in_avail;
         b->in_pos = s->rc.in_pos;
     }
 
     in_avail = b->in_size - b->in_pos;
     if (in_avail < LZMA_IN_REQUIRED) {
         if (in_avail > s->lzma2.compressed)
             in_avail = s->lzma2.compressed;
 
         memcpy(s->temp.buf, b->in + b->in_pos, in_avail);
         s->temp.size = in_avail;
         b->in_pos += in_avail;
     }
 
     return true;
 }
 
 /*
  * Take care of the LZMA2 control layer, and forward the job of actual LZMA
  * decoding or copying of uncompressed chunks to other functions.
  */
 XZ_EXTERN enum xz_ret xz_dec_lzma2_run(struct xz_dec_lzma2 *s,
                        struct xz_buf *b)
 {
     uint32_t tmp;
 
     while (b->in_pos < b->in_size || s->lzma2.sequence == SEQ_LZMA_RUN) {
         switch (s->lzma2.sequence) {
         case SEQ_CONTROL:
             /*
              * LZMA2 control byte
              *
              * Exact values:
              *   0x00   End marker
              *   0x01   Dictionary reset followed by
              *          an uncompressed chunk
              *   0x02   Uncompressed chunk (no dictionary reset)
              *
              * Highest three bits (s->control & 0xE0):
              *   0xE0   Dictionary reset, new properties and state
              *          reset, followed by LZMA compressed chunk
              *   0xC0   New properties and state reset, followed
              *          by LZMA compressed chunk (no dictionary
              *          reset)
              *   0xA0   State reset using old properties,
              *          followed by LZMA compressed chunk (no
              *          dictionary reset)
              *   0x80   LZMA chunk (no dictionary or state reset)
              *
              * For LZMA compressed chunks, the lowest five bits
              * (s->control & 1F) are the highest bits of the
              * uncompressed size (bits 16-20).
              *
              * A new LZMA2 stream must begin with a dictionary
              * reset. The first LZMA chunk must set new
              * properties and reset the LZMA state.
              *
              * Values that don't match anything described above
              * are invalid and we return XZ_DATA_ERROR.
              */
             tmp = b->in[b->in_pos++];
 
             if (tmp == 0x00)
                 return XZ_STREAM_END;
 
             if (tmp >= 0xE0 || tmp == 0x01) {
                 s->lzma2.need_props = true;
                 s->lzma2.need_dict_reset = false;
                 dict_reset(&s->dict, b);
             } else if (s->lzma2.need_dict_reset) {
                 return XZ_DATA_ERROR;
             }
 
             if (tmp >= 0x80) {
                 s->lzma2.uncompressed = (tmp & 0x1F) << 16;
                 s->lzma2.sequence = SEQ_UNCOMPRESSED_1;
 
                 if (tmp >= 0xC0) {
                     /*
                      * When there are new properties,
                      * state reset is done at
                      * SEQ_PROPERTIES.
                      */
                     s->lzma2.need_props = false;
                     s->lzma2.next_sequence
                             = SEQ_PROPERTIES;
 
                 } else if (s->lzma2.need_props) {
                     return XZ_DATA_ERROR;
 
                 } else {
                     s->lzma2.next_sequence
                             = SEQ_LZMA_PREPARE;
                     if (tmp >= 0xA0)
                         lzma_reset(s);
                 }
             } else {
                 if (tmp > 0x02)
                     return XZ_DATA_ERROR;
 
                 s->lzma2.sequence = SEQ_COMPRESSED_0;
                 s->lzma2.next_sequence = SEQ_COPY;
             }
 
             break;
 
         case SEQ_UNCOMPRESSED_1:
             s->lzma2.uncompressed
                     += (uint32_t)b->in[b->in_pos++] << 8;
             s->lzma2.sequence = SEQ_UNCOMPRESSED_2;
             break;
 
         case SEQ_UNCOMPRESSED_2:
             s->lzma2.uncompressed
                     += (uint32_t)b->in[b->in_pos++] + 1;
             s->lzma2.sequence = SEQ_COMPRESSED_0;
             break;
 
         case SEQ_COMPRESSED_0:
             s->lzma2.compressed
                     = (uint32_t)b->in[b->in_pos++] << 8;
             s->lzma2.sequence = SEQ_COMPRESSED_1;
             break;
 
         case SEQ_COMPRESSED_1:
             s->lzma2.compressed
                     += (uint32_t)b->in[b->in_pos++] + 1;
             s->lzma2.sequence = s->lzma2.next_sequence;
             break;
 
         case SEQ_PROPERTIES:
             if (!lzma_props(s, b->in[b->in_pos++]))
                 return XZ_DATA_ERROR;
 
             s->lzma2.sequence = SEQ_LZMA_PREPARE;
 
         /* Fall through */
 
         case SEQ_LZMA_PREPARE:
             if (s->lzma2.compressed < RC_INIT_BYTES)
                 return XZ_DATA_ERROR;
 
             if (!rc_read_init(&s->rc, b))
                 return XZ_OK;
 
             s->lzma2.compressed -= RC_INIT_BYTES;
             s->lzma2.sequence = SEQ_LZMA_RUN;
 
         /* Fall through */
 
         case SEQ_LZMA_RUN:
             /*
              * Set dictionary limit to indicate how much we want
              * to be encoded at maximum. Decode new data into the
              * dictionary. Flush the new data from dictionary to
              * b->out. Check if we finished decoding this chunk.
              * In case the dictionary got full but we didn't fill
              * the output buffer yet, we may run this loop
              * multiple times without changing s->lzma2.sequence.
              */
             dict_limit(&s->dict, min_t(size_t,
                     b->out_size - b->out_pos,
                     s->lzma2.uncompressed));
             if (!lzma2_lzma(s, b))
                 return XZ_DATA_ERROR;
 
             s->lzma2.uncompressed -= dict_flush(&s->dict, b);
 
             if (s->lzma2.uncompressed == 0) {
                 if (s->lzma2.compressed > 0 || s->lzma.len > 0
                         || !rc_is_finished(&s->rc))
                     return XZ_DATA_ERROR;
 
                 rc_reset(&s->rc);
                 s->lzma2.sequence = SEQ_CONTROL;
 
             } else if (b->out_pos == b->out_size
                     || (b->in_pos == b->in_size
                         && s->temp.size
                         < s->lzma2.compressed)) {
                 return XZ_OK;
             }
 
             break;
 
         case SEQ_COPY:
             dict_uncompressed(&s->dict, b, &s->lzma2.compressed);
             if (s->lzma2.compressed > 0)
                 return XZ_OK;
 
             s->lzma2.sequence = SEQ_CONTROL;
             break;
         }
     }
 
     return XZ_OK;
 }
 
 XZ_EXTERN struct xz_dec_lzma2 *xz_dec_lzma2_create(enum xz_mode mode,
                            uint32_t dict_max)
 {
     struct xz_dec_lzma2 *s = kmalloc(sizeof(*s), GFP_KERNEL);
     if (s == NULL)
         return NULL;
 
     s->dict.mode = mode;
     s->dict.size_max = dict_max;
 
     if (DEC_IS_PREALLOC(mode)) {
         s->dict.buf = vmalloc(dict_max);
         if (s->dict.buf == NULL) {
             kfree(s);
             return NULL;
         }
     } else if (DEC_IS_DYNALLOC(mode)) {
         s->dict.buf = NULL;
         s->dict.allocated = 0;
     }
 
     return s;
 }
 
 XZ_EXTERN enum xz_ret xz_dec_lzma2_reset(struct xz_dec_lzma2 *s, uint8_t props)
 {
     /* This limits dictionary size to 3 GiB to keep parsing simpler. */
     if (props > 39)
         return XZ_OPTIONS_ERROR;
 
     s->dict.size = 2 + (props & 1);
     s->dict.size <<= (props >> 1) + 11;
 
     if (DEC_IS_MULTI(s->dict.mode)) {
         if (s->dict.size > s->dict.size_max)
             return XZ_MEMLIMIT_ERROR;
 
         s->dict.end = s->dict.size;
 
         if (DEC_IS_DYNALLOC(s->dict.mode)) {
             if (s->dict.allocated < s->dict.size) {
                 vfree(s->dict.buf);
                 s->dict.buf = vmalloc(s->dict.size);
                 if (s->dict.buf == NULL) {
                     s->dict.allocated = 0;
                     return XZ_MEM_ERROR;
                 }
             }
         }
     }
 
     s->lzma.len = 0;
 
     s->lzma2.sequence = SEQ_CONTROL;
     s->lzma2.need_dict_reset = true;
 
     s->temp.size = 0;
 
     return XZ_OK;
 }
 
 XZ_EXTERN void xz_dec_lzma2_end(struct xz_dec_lzma2 *s)
 {
     if (DEC_IS_MULTI(s->dict.mode))
         vfree(s->dict.buf);
 
     kfree(s);
 }

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