FreeBSD/Linux Kernel Cross Reference
sys/contrib/xz-embedded/linux/lib/xz/xz_dec_lzma2.c

     /*
      * LZMA2 decoder
      *
      * Authors: Lasse Collin <lasse.collin@tukaani.org>
      *          Igor Pavlov <https://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 derived from the number of literal
            * position bits, and a mask derived 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;
   
   #ifdef XZ_DEC_MICROLZMA
           bool pedantic_microlzma;
   #endif
   };
   
   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;
   
                   /*
                    * If doing in-place decompression in single-call mode and the
                    * uncompressed size of the file is larger than the caller
                    * thought (i.e. it is invalid input!), the buffers below may
                    * overlap and cause undefined behavior with memcpy().
                    * With valid inputs memcpy() would be fine here.
                    */
                   memmove(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;
   
                           /*
                            * Like above but for multi-call mode: use memmove()
                            * to avoid undefined behavior with invalid input.
                            */
                           memmove(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;
           }
   }
   
   #ifdef XZ_DEC_MICROLZMA
   #       define DICT_FLUSH_SUPPORTS_SKIPPING true
   #else
   #       define DICT_FLUSH_SUPPORTS_SKIPPING false
   #endif
   
   /*
    * 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;
   
                   /*
                    * These buffers cannot overlap even if doing in-place
                    * decompression because in multi-call mode dict->buf
                    * has been allocated by us in this file; it's not
                    * provided by the caller like in single-call mode.
                    *
                    * With MicroLZMA, b->out can be NULL to skip bytes that
                    * the caller doesn't need. This cannot be done with XZ
                    * because it would break BCJ filters.
                    */
                   if (!DICT_FLUSH_SUPPORTS_SKIPPING || b->out != NULL)
                           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;
   }
   
   /* 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 split 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-split 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);
   }
   
   /* 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 not 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;
           s->lzma.len = 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) {
                                  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->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);
  }
  
  #ifdef XZ_DEC_MICROLZMA
  /* This is a wrapper struct to have a nice struct name in the public API. */
  struct xz_dec_microlzma {
          struct xz_dec_lzma2 s;
  };
  
  enum xz_ret xz_dec_microlzma_run(struct xz_dec_microlzma *s_ptr,
                                   struct xz_buf *b)
  {
          struct xz_dec_lzma2 *s = &s_ptr->s;
  
          /*
           * sequence is SEQ_PROPERTIES before the first input byte,
           * SEQ_LZMA_PREPARE until a total of five bytes have been read,
           * and SEQ_LZMA_RUN for the rest of the input stream.
           */
          if (s->lzma2.sequence != SEQ_LZMA_RUN) {
                  if (s->lzma2.sequence == SEQ_PROPERTIES) {
                          /* One byte is needed for the props. */
                          if (b->in_pos >= b->in_size)
                                  return XZ_OK;
  
                          /*
                           * Don't increment b->in_pos here. The same byte is
                           * also passed to rc_read_init() which will ignore it.
                           */
                          if (!lzma_props(s, ~b->in[b->in_pos]))
                                  return XZ_DATA_ERROR;
  
                          s->lzma2.sequence = SEQ_LZMA_PREPARE;
                  }
  
                  /*
                   * xz_dec_microlzma_reset() doesn't validate the compressed
                   * size so we do it here. We have to limit the maximum size
                   * to avoid integer overflows in lzma2_lzma(). 3 GiB is a nice
                   * round number and much more than users of this code should
                   * ever need.
                   */
                  if (s->lzma2.compressed < RC_INIT_BYTES
                                  || s->lzma2.compressed > (3U << 30))
                          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;
  
                  dict_reset(&s->dict, b);
          }
  
          /* This is to allow increasing b->out_size between calls. */
          if (DEC_IS_SINGLE(s->dict.mode))
                  s->dict.end = b->out_size - b->out_pos;
  
          while (true) {
                  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.pedantic_microlzma) {
                                  if (s->lzma2.compressed > 0 || s->lzma.len > 0
                                                  || !rc_is_finished(&s->rc))
                                          return XZ_DATA_ERROR;
                          }
  
                          return XZ_STREAM_END;
                  }
  
                  if (b->out_pos == b->out_size)
                          return XZ_OK;
  
                  if (b->in_pos == b->in_size
                                  && s->temp.size < s->lzma2.compressed)
                          return XZ_OK;
          }
  }
  
  struct xz_dec_microlzma *xz_dec_microlzma_alloc(enum xz_mode mode,
                                                  uint32_t dict_size)
  {
          struct xz_dec_microlzma *s;
  
          /* Restrict dict_size to the same range as in the LZMA2 code. */
          if (dict_size < 4096 || dict_size > (3U << 30))
                  return NULL;
  
          s = kmalloc(sizeof(*s), GFP_KERNEL);
          if (s == NULL)
                  return NULL;
  
          s->s.dict.mode = mode;
          s->s.dict.size = dict_size;
  
          if (DEC_IS_MULTI(mode)) {
                  s->s.dict.end = dict_size;
  
                  s->s.dict.buf = vmalloc(dict_size);
                  if (s->s.dict.buf == NULL) {
                          kfree(s);
                          return NULL;
                  }
          }
  
          return s;
  }
  
  void xz_dec_microlzma_reset(struct xz_dec_microlzma *s, uint32_t comp_size,
                              uint32_t uncomp_size, int uncomp_size_is_exact)
  {
          /*
           * comp_size is validated in xz_dec_microlzma_run().
           * uncomp_size can safely be anything.
           */
          s->s.lzma2.compressed = comp_size;
          s->s.lzma2.uncompressed = uncomp_size;
          s->s.lzma2.pedantic_microlzma = uncomp_size_is_exact;
  
          s->s.lzma2.sequence = SEQ_PROPERTIES;
          s->s.temp.size = 0;
  }
  
  void xz_dec_microlzma_end(struct xz_dec_microlzma *s)
  {
          if (DEC_IS_MULTI(s->s.dict.mode))
                  vfree(s->s.dict.buf);
  
          kfree(s);
  }
  #endif

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