Linux 3.8-rc7

[cris-mirror.git] / lib / xz / xz_dec_lzma2.c

/*
 * 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;
}

/* 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);
}

/* 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;

                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;

                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);
}