Fix version.sh compatiblity with Solaris

[xz/debian.git] / src / liblzma / lzma / lzma_decoder.c

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       lzma_decoder.c
/// \brief      LZMA decoder
///
//  Authors:    Igor Pavlov
//              Lasse Collin
//              Jia Tan
//
///////////////////////////////////////////////////////////////////////////////

#include "lz_decoder.h"
#include "lzma_common.h"
#include "lzma_decoder.h"
#include "range_decoder.h"

// The macros unroll loops with switch statements.
// Silence warnings about missing fall-through comments.
#if TUKLIB_GNUC_REQ(7, 0)
#       pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
#endif

// Minimum number of input bytes 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 20 bytes of input.
#define LZMA_IN_REQUIRED 20


// Macros for (somewhat) size-optimized code.
// This is used to decode the match length (how many bytes must be repeated
// from the dictionary). This version is used in the Resumable mode and
// does not unroll any loops.
#define len_decode(target, ld, pos_state, seq) \
do { \
case seq ## _CHOICE: \
        rc_if_0_safe(ld.choice, seq ## _CHOICE) { \
                rc_update_0(ld.choice); \
                probs = ld.low[pos_state];\
                limit = LEN_LOW_SYMBOLS; \
                target = MATCH_LEN_MIN; \
        } else { \
                rc_update_1(ld.choice); \
case seq ## _CHOICE2: \
                rc_if_0_safe(ld.choice2, seq ## _CHOICE2) { \
                        rc_update_0(ld.choice2); \
                        probs = ld.mid[pos_state]; \
                        limit = LEN_MID_SYMBOLS; \
                        target = MATCH_LEN_MIN + LEN_LOW_SYMBOLS; \
                } else { \
                        rc_update_1(ld.choice2); \
                        probs = ld.high; \
                        limit = LEN_HIGH_SYMBOLS; \
                        target = MATCH_LEN_MIN + LEN_LOW_SYMBOLS \
                                        + LEN_MID_SYMBOLS; \
                } \
        } \
        symbol = 1; \
case seq ## _BITTREE: \
        do { \
                rc_bit_safe(probs[symbol], , , seq ## _BITTREE); \
        } while (symbol < limit); \
        target += symbol - limit; \
} while (0)


// This is the faster version of the match length decoder that does not
// worry about being resumable. It unrolls the bittree decoding loop.
#define len_decode_fast(target, ld, pos_state) \
do { \
        symbol = 1; \
        rc_if_0(ld.choice) { \
                rc_update_0(ld.choice); \
                rc_bittree3(ld.low[pos_state], \
                                -LEN_LOW_SYMBOLS + MATCH_LEN_MIN); \
                target = symbol; \
        } else { \
                rc_update_1(ld.choice); \
                rc_if_0(ld.choice2) { \
                        rc_update_0(ld.choice2); \
                        rc_bittree3(ld.mid[pos_state], -LEN_MID_SYMBOLS \
                                        + MATCH_LEN_MIN + LEN_LOW_SYMBOLS); \
                        target = symbol; \
                } else { \
                        rc_update_1(ld.choice2); \
                        rc_bittree8(ld.high, -LEN_HIGH_SYMBOLS \
                                        + MATCH_LEN_MIN \
                                        + LEN_LOW_SYMBOLS + LEN_MID_SYMBOLS); \
                        target = symbol; \
                } \
        } \
} while (0)


/// Length decoder probabilities; see comments in lzma_common.h.
typedef struct {
        probability choice;
        probability choice2;
        probability low[POS_STATES_MAX][LEN_LOW_SYMBOLS];
        probability mid[POS_STATES_MAX][LEN_MID_SYMBOLS];
        probability high[LEN_HIGH_SYMBOLS];
} lzma_length_decoder;


typedef struct {
        ///////////////////
        // Probabilities //
        ///////////////////

        /// Literals; see comments in lzma_common.h.
        probability literal[LITERAL_CODERS_MAX * LITERAL_CODER_SIZE];

        /// If 1, it's a match. Otherwise it's a single 8-bit literal.
        probability is_match[STATES][POS_STATES_MAX];

        /// If 1, it's a repeated match. The distance is one of rep0 .. rep3.
        probability is_rep[STATES];

        /// If 0, distance of a repeated match is rep0.
        /// Otherwise check is_rep1.
        probability is_rep0[STATES];

        /// If 0, distance of a repeated match is rep1.
        /// Otherwise check is_rep2.
        probability is_rep1[STATES];

        /// If 0, distance of a repeated match is rep2. Otherwise it is rep3.
        probability is_rep2[STATES];

        /// If 1, the repeated match has length of one byte. Otherwise
        /// the length is decoded from rep_len_decoder.
        probability 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].
        probability dist_slot[DIST_STATES][DIST_SLOTS];

        /// Probability trees for additional bits for match distance when the
        /// distance is in the range [4, 127].
        probability pos_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.
        probability pos_align[ALIGN_SIZE];

        /// Length of a normal match
        lzma_length_decoder match_len_decoder;

        /// Length of a repeated match
        lzma_length_decoder rep_len_decoder;

        ///////////////////
        // Decoder state //
        ///////////////////

        // Range coder
        lzma_range_decoder rc;

        // Types of the most recently seen LZMA symbols
        lzma_lzma_state state;

        uint32_t rep0;      ///< Distance of the latest match
        uint32_t rep1;      ///< Distance of second latest match
        uint32_t rep2;      ///< Distance of third latest match
        uint32_t rep3;      ///< Distance of fourth latest match

        uint32_t pos_mask; // (1U << pb) - 1
        uint32_t literal_context_bits;
        uint32_t literal_mask;

        /// Uncompressed size as bytes, or LZMA_VLI_UNKNOWN if end of
        /// payload marker is expected.
        lzma_vli uncompressed_size;

        /// True if end of payload marker (EOPM) is allowed even when
        /// uncompressed_size is known; false if EOPM must not be present.
        /// This is ignored if uncompressed_size == LZMA_VLI_UNKNOWN.
        bool allow_eopm;

        ////////////////////////////////
        // State of incomplete symbol //
        ////////////////////////////////

        /// Position where to continue the decoder loop
        enum {
                SEQ_NORMALIZE,
                SEQ_IS_MATCH,
                SEQ_LITERAL,
                SEQ_LITERAL_MATCHED,
                SEQ_LITERAL_WRITE,
                SEQ_IS_REP,
                SEQ_MATCH_LEN_CHOICE,
                SEQ_MATCH_LEN_CHOICE2,
                SEQ_MATCH_LEN_BITTREE,
                SEQ_DIST_SLOT,
                SEQ_DIST_MODEL,
                SEQ_DIRECT,
                SEQ_ALIGN,
                SEQ_EOPM,
                SEQ_IS_REP0,
                SEQ_SHORTREP,
                SEQ_IS_REP0_LONG,
                SEQ_IS_REP1,
                SEQ_IS_REP2,
                SEQ_REP_LEN_CHOICE,
                SEQ_REP_LEN_CHOICE2,
                SEQ_REP_LEN_BITTREE,
                SEQ_COPY,
        } sequence;

        /// Base of the current probability tree
        probability *probs;

        /// Symbol being decoded. This is also used as an index variable in
        /// bittree decoders: probs[symbol]
        uint32_t symbol;

        /// Used as a loop termination condition on bittree decoders and
        /// direct bits decoder.
        uint32_t limit;

        /// Matched literal decoder: 0x100 or 0 to help avoiding branches.
        /// Bittree reverse decoders: Offset of the next bit: 1 << offset
        uint32_t offset;

        /// If decoding a literal: match byte.
        /// If decoding a match: length of the match.
        uint32_t len;
} lzma_lzma1_decoder;


static lzma_ret
lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
                const uint8_t *restrict in,
                size_t *restrict in_pos, size_t in_size)
{
        lzma_lzma1_decoder *restrict coder = coder_ptr;

        ////////////////////
        // Initialization //
        ////////////////////

        {
                const lzma_ret ret = rc_read_init(
                                &coder->rc, in, in_pos, in_size);
                if (ret != LZMA_STREAM_END)
                        return ret;
        }

        ///////////////
        // Variables //
        ///////////////

        // Making local copies of often-used variables improves both
        // speed and readability.

        lzma_dict dict = *dictptr;

        const size_t dict_start = dict.pos;

        // Range decoder
        rc_to_local(coder->rc, *in_pos, LZMA_IN_REQUIRED);

        // State
        uint32_t state = coder->state;
        uint32_t rep0 = coder->rep0;
        uint32_t rep1 = coder->rep1;
        uint32_t rep2 = coder->rep2;
        uint32_t rep3 = coder->rep3;

        const uint32_t pos_mask = coder->pos_mask;

        // These variables are actually needed only if we last time ran
        // out of input in the middle of the decoder loop.
        probability *probs = coder->probs;
        uint32_t symbol = coder->symbol;
        uint32_t limit = coder->limit;
        uint32_t offset = coder->offset;
        uint32_t len = coder->len;

        const uint32_t literal_mask = coder->literal_mask;
        const uint32_t literal_context_bits = coder->literal_context_bits;

        // Temporary variables
        uint32_t pos_state = dict.pos & pos_mask;

        lzma_ret ret = LZMA_OK;

        // This is true when the next LZMA symbol is allowed to be EOPM.
        // That is, if this is false, then EOPM is considered
        // an invalid symbol and we will return LZMA_DATA_ERROR.
        //
        // EOPM is always required (not just allowed) when
        // the uncompressed size isn't known. When uncompressed size
        // is known, eopm_is_valid may be set to true later.
        bool eopm_is_valid = coder->uncompressed_size == LZMA_VLI_UNKNOWN;

        // If uncompressed size is known and there is enough output space
        // to decode all the data, limit the available buffer space so that
        // the main loop won't try to decode past the end of the stream.
        bool might_finish_without_eopm = false;
        if (coder->uncompressed_size != LZMA_VLI_UNKNOWN
                        && coder->uncompressed_size <= dict.limit - dict.pos) {
                dict.limit = dict.pos + (size_t)(coder->uncompressed_size);
                might_finish_without_eopm = true;
        }

        // The main decoder loop. The "switch" is used to resume the decoder at
        // correct location. Once resumed, the "switch" is no longer used.
        // The decoder loops is split into two modes:
        //
        // 1 - Non-resumable mode (fast). This is used when it is guaranteed
        //     there is enough input to decode the next symbol. If the output
        //     limit is reached, then the decoder loop will save the place
        //     for the resumable mode to continue. This mode is not used if
        //     HAVE_SMALL is defined. This is faster than Resumable mode
        //     because it reduces the number of branches needed and allows
        //     for more compiler optimizations.
        //
        // 2 - Resumable mode (slow). This is used when a previous decoder
        //     loop did not have enough space in the input or output buffers
        //     to complete. It uses sequence enum values to set remind
        //     coder->sequence where to resume in the decoder loop. This
        //     is the only mode used when HAVE_SMALL is defined.

        switch (coder->sequence)
        while (true) {
                // Calculate new pos_state. This is skipped on the first loop
                // since we already calculated it when setting up the local
                // variables.
                pos_state = dict.pos & pos_mask;

#ifndef HAVE_SMALL

                ///////////////////////////////
                // Non-resumable Mode (fast) //
                ///////////////////////////////

                // Go to Resumable mode (1) if there is not enough input to
                // safely decode any possible LZMA symbol or (2) if the
                // dictionary is full, which may need special checks that
                // are only done in the Resumable mode.
                if (unlikely(!rc_is_fast_allowed()
                                || dict.pos == dict.limit))
                        goto slow;

                // Decode the first bit from the next LZMA symbol.
                // If the bit is a 0, then we handle it as a literal.
                // If the bit is a 1, then it is a match of previously
                // decoded data.
                rc_if_0(coder->is_match[state][pos_state]) {
                        /////////////////////
                        // Decode literal. //
                        /////////////////////

                        // Update the RC that we have decoded a 0.
                        rc_update_0(coder->is_match[state][pos_state]);

                        // Get the correct probability array from lp and
                        // lc params.
                        probs = literal_subcoder(coder->literal,
                                        literal_context_bits, literal_mask,
                                        dict.pos, dict_get0(&dict));

                        if (is_literal_state(state)) {
                                update_literal_normal(state);

                                // Decode literal without match byte.
                                rc_bittree8(probs, 0);
                        } else {
                                update_literal_matched(state);

                                // Decode literal with match byte.
                                rc_matched_literal(probs,
                                                dict_get(&dict, rep0));
                        }

                        // Write decoded literal to dictionary
                        dict_put(&dict, symbol);
                        continue;
                }

                ///////////////////
                // Decode match. //
                ///////////////////

                // Instead of a new byte we are going to decode a
                // distance-length pair. The distance represents how far
                // back in the dictionary to begin copying. The length
                // represents how many bytes to copy.

                rc_update_1(coder->is_match[state][pos_state]);

                rc_if_0(coder->is_rep[state]) {
                        ///////////////////
                        // Simple match. //
                        ///////////////////

                        // Not a repeated match. In this case,
                        // the length (how many bytes to copy) must be
                        // decoded first. Then, the distance (where to
                        // start copying) is decoded.
                        //
                        // This is also how we know when we are done
                        // decoding. If the distance decodes to UINT32_MAX,
                        // then we know to stop decoding (end of payload
                        // marker).

                        rc_update_0(coder->is_rep[state]);
                        update_match(state);

                        // The latest three match distances are kept in
                        // memory in case there are repeated matches.
                        rep3 = rep2;
                        rep2 = rep1;
                        rep1 = rep0;

                        // Decode the length of the match.
                        len_decode_fast(len, coder->match_len_decoder,
                                        pos_state);

                        // Next, decode the distance into rep0.

                        // The next 6 bits determine how to decode the
                        // rest of the distance.
                        probs = coder->dist_slot[get_dist_state(len)];

                        rc_bittree6(probs, -DIST_SLOTS);
                        assert(symbol <= 63);

                        if (symbol < DIST_MODEL_START) {
                                // If the decoded symbol is < DIST_MODEL_START
                                // then we use its value directly as the
                                // match distance. No other bits are needed.
                                // The only possible distance values
                                // are [0, 3].
                                rep0 = symbol;
                        } else {
                                // Use the first two bits of symbol as the
                                // highest bits of the match distance.

                                // "limit" represents the number of low bits
                                // to decode.
                                limit = (symbol >> 1) - 1;
                                assert(limit >= 1 && limit <= 30);
                                rep0 = 2 + (symbol & 1);

                                if (symbol < DIST_MODEL_END) {
                                        // When symbol is > DIST_MODEL_START,
                                        // but symbol < DIST_MODEL_END, then
                                        // it can decode distances between
                                        // [4, 127].
                                        assert(limit <= 5);
                                        rep0 <<= limit;
                                        assert(rep0 <= 96);

                                        // -1 is fine, because we start
                                        // decoding at probs[1], not probs[0].
                                        // NOTE: This violates the C standard,
                                        // since we are doing pointer
                                        // arithmetic past the beginning of
                                        // the array.
                                        assert((int32_t)(rep0 - symbol - 1)
                                                        >= -1);
                                        assert((int32_t)(rep0 - symbol - 1)
                                                        <= 82);
                                        probs = coder->pos_special + rep0
                                                        - symbol - 1;
                                        symbol = 1;
                                        offset = 1;

                                        // Variable number (1-5) of bits
                                        // from a reverse bittree. This
                                        // isn't worth manual unrolling.
                                        //
                                        // NOTE: Making one or many of the
                                        // variables (probs, symbol, offset,
                                        // or limit) local here (instead of
                                        // using those declared outside the
                                        // main loop) can affect code size
                                        // and performance which isn't a
                                        // surprise but it's not so clear
                                        // what is the best.
                                        do {
                                                rc_bit_add_if_1(probs,
                                                                rep0, offset);
                                                offset <<= 1;
                                        } while (--limit > 0);
                                } else {
                                        // The distance is >= 128. Decode the
                                        // lower bits without probabilities
                                        // except the lowest four bits.
                                        assert(symbol >= 14);
                                        assert(limit >= 6);

                                        limit -= ALIGN_BITS;
                                        assert(limit >= 2);

                                        rc_direct(rep0, limit);

                                        // Decode the lowest four bits using
                                        // probabilities.
                                        rep0 <<= ALIGN_BITS;
                                        rc_bittree_rev4(coder->pos_align);
                                        rep0 += symbol;

                                        // If the end of payload marker (EOPM)
                                        // is detected, jump to the safe code.
                                        // The EOPM handling isn't speed
                                        // critical at all.
                                        //
                                        // A final normalization is needed
                                        // after the EOPM (there can be a
                                        // dummy byte to read in some cases).
                                        // If the normalization was done here
                                        // in the fast code, it would need to
                                        // be taken into account in the value
                                        // of LZMA_IN_REQUIRED. Using the
                                        // safe code allows keeping
                                        // LZMA_IN_REQUIRED as 20 instead of
                                        // 21.
                                        if (rep0 == UINT32_MAX)
                                                goto eopm;
                                }
                        }

                        // Validate the distance we just decoded.
                        if (unlikely(!dict_is_distance_valid(&dict, rep0))) {
                                ret = LZMA_DATA_ERROR;
                                goto out;
                        }

                } else {
                        rc_update_1(coder->is_rep[state]);

                        /////////////////////
                        // Repeated match. //
                        /////////////////////

                        // The match distance is a value that we have decoded
                        // recently. The latest four match distances are
                        // available as rep0, rep1, rep2 and rep3. We will
                        // now decode which of them is the new distance.
                        //
                        // There cannot be a match if we haven't produced
                        // any output, so check that first.
                        if (unlikely(!dict_is_distance_valid(&dict, 0))) {
                                ret = LZMA_DATA_ERROR;
                                goto out;
                        }

                        rc_if_0(coder->is_rep0[state]) {
                                rc_update_0(coder->is_rep0[state]);
                                // The distance is rep0.

                                // Decode the next bit to determine if 1 byte
                                // should be copied from rep0 distance or
                                // if the number of bytes needs to be decoded.

                                // If the next bit is 0, then it is a
                                // "Short Rep Match" and only 1 bit is copied.
                                // Otherwise, the length of the match is
                                // decoded after the "else" statement.
                                rc_if_0(coder->is_rep0_long[state][pos_state]) {
                                        rc_update_0(coder->is_rep0_long[
                                                        state][pos_state]);

                                        update_short_rep(state);
                                        dict_put(&dict, dict_get(&dict, rep0));
                                        continue;
                                }

                                // Repeating more than one byte at
                                // distance of rep0.
                                rc_update_1(coder->is_rep0_long[
                                                state][pos_state]);

                        } else {
                                rc_update_1(coder->is_rep0[state]);

                                // The distance is rep1, rep2 or rep3. Once
                                // we find out which one of these three, it
                                // is stored to rep0 and rep1, rep2 and rep3
                                // are updated accordingly. There is no
                                // "Short Rep Match" option, so the length
                                // of the match must always be decoded next.
                                rc_if_0(coder->is_rep1[state]) {
                                        // The distance is rep1.
                                        rc_update_0(coder->is_rep1[state]);

                                        const uint32_t distance = rep1;
                                        rep1 = rep0;
                                        rep0 = distance;

                                } else {
                                        rc_update_1(coder->is_rep1[state]);

                                        rc_if_0(coder->is_rep2[state]) {
                                                // The distance is rep2.
                                                rc_update_0(coder->is_rep2[
                                                                state]);

                                                const uint32_t distance = rep2;
                                                rep2 = rep1;
                                                rep1 = rep0;
                                                rep0 = distance;

                                        } else {
                                                // The distance is rep3.
                                                rc_update_1(coder->is_rep2[
                                                                state]);

                                                const uint32_t distance = rep3;
                                                rep3 = rep2;
                                                rep2 = rep1;
                                                rep1 = rep0;
                                                rep0 = distance;
                                        }
                                }
                        }

                        update_long_rep(state);

                        // Decode the length of the repeated match.
                        len_decode_fast(len, coder->rep_len_decoder,
                                        pos_state);
                }

                /////////////////////////////////
                // Repeat from history buffer. //
                /////////////////////////////////

                // The length is always between these limits. There is no way
                // to trigger the algorithm to set len outside this range.
                assert(len >= MATCH_LEN_MIN);
                assert(len <= MATCH_LEN_MAX);

                // Repeat len bytes from distance of rep0.
                if (unlikely(dict_repeat(&dict, rep0, &len))) {
                        coder->sequence = SEQ_COPY;
                        goto out;
                }

                continue;

slow:
#endif
        ///////////////////////////
        // Resumable Mode (slow) //
        ///////////////////////////

        // This is very similar to Non-resumable Mode, so most of the
        // comments are not repeated. The main differences are:
        // - case labels are used to resume at the correct location.
        // - Loops are not unrolled.
        // - Range coder macros take an extra sequence argument
        //   so they can save to coder->sequence the location to
        //   resume in case there is not enough input.
        case SEQ_NORMALIZE:
        case SEQ_IS_MATCH:
                if (unlikely(might_finish_without_eopm
                                && dict.pos == dict.limit)) {
                        // In rare cases there is a useless byte that needs
                        // to be read anyway.
                        rc_normalize_safe(SEQ_NORMALIZE);

                        // If the range decoder state is such that we can
                        // be at the end of the LZMA stream, then the
                        // decoding is finished.
                        if (rc_is_finished(rc)) {
                                ret = LZMA_STREAM_END;
                                goto out;
                        }

                        // If the caller hasn't allowed EOPM to be present
                        // together with known uncompressed size, then the
                        // LZMA stream is corrupt.
                        if (!coder->allow_eopm) {
                                ret = LZMA_DATA_ERROR;
                                goto out;
                        }

                        // Otherwise continue decoding with the expectation
                        // that the next LZMA symbol is EOPM.
                        eopm_is_valid = true;
                }

                rc_if_0_safe(coder->is_match[state][pos_state], SEQ_IS_MATCH) {
                        /////////////////////
                        // Decode literal. //
                        /////////////////////

                        rc_update_0(coder->is_match[state][pos_state]);

                        probs = literal_subcoder(coder->literal,
                                        literal_context_bits, literal_mask,
                                        dict.pos, dict_get0(&dict));
                        symbol = 1;

                        if (is_literal_state(state)) {
                                update_literal_normal(state);

                                // Decode literal without match byte.
                                // The "slow" version does not unroll
                                // the loop.
        case SEQ_LITERAL:
                                do {
                                        rc_bit_safe(probs[symbol], , ,
                                                        SEQ_LITERAL);
                                } while (symbol < (1 << 8));
                        } else {
                                update_literal_matched(state);

                                // Decode literal with match byte.
                                len = (uint32_t)(dict_get(&dict, rep0)) << 1;

                                offset = 0x100;

        case SEQ_LITERAL_MATCHED:
                                do {
                                        const uint32_t match_bit
                                                        = len & offset;
                                        const uint32_t subcoder_index
                                                        = offset + match_bit
                                                        + symbol;

                                        rc_bit_safe(probs[subcoder_index],
                                                        offset &= ~match_bit,
                                                        offset &= match_bit,
                                                        SEQ_LITERAL_MATCHED);

                                        // It seems to be faster to do this
                                        // here instead of putting it to the
                                        // beginning of the loop and then
                                        // putting the "case" in the middle
                                        // of the loop.
                                        len <<= 1;

                                } while (symbol < (1 << 8));
                        }

        case SEQ_LITERAL_WRITE:
                        if (dict_put_safe(&dict, symbol)) {
                                coder->sequence = SEQ_LITERAL_WRITE;
                                goto out;
                        }

                        continue;
                }

                ///////////////////
                // Decode match. //
                ///////////////////

                rc_update_1(coder->is_match[state][pos_state]);

        case SEQ_IS_REP:
                rc_if_0_safe(coder->is_rep[state], SEQ_IS_REP) {
                        ///////////////////
                        // Simple match. //
                        ///////////////////

                        rc_update_0(coder->is_rep[state]);
                        update_match(state);

                        rep3 = rep2;
                        rep2 = rep1;
                        rep1 = rep0;

                        len_decode(len, coder->match_len_decoder,
                                        pos_state, SEQ_MATCH_LEN);

                        probs = coder->dist_slot[get_dist_state(len)];
                        symbol = 1;

        case SEQ_DIST_SLOT:
                        do {
                                rc_bit_safe(probs[symbol], , , SEQ_DIST_SLOT);
                        } while (symbol < DIST_SLOTS);

                        symbol -= DIST_SLOTS;
                        assert(symbol <= 63);

                        if (symbol < DIST_MODEL_START) {
                                rep0 = symbol;
                        } else {
                                limit = (symbol >> 1) - 1;
                                assert(limit >= 1 && limit <= 30);
                                rep0 = 2 + (symbol & 1);

                                if (symbol < DIST_MODEL_END) {
                                        assert(limit <= 5);
                                        rep0 <<= limit;
                                        assert(rep0 <= 96);
                                        // -1 is fine, because we start
                                        // decoding at probs[1], not probs[0].
                                        // NOTE: This violates the C standard,
                                        // since we are doing pointer
                                        // arithmetic past the beginning of
                                        // the array.
                                        assert((int32_t)(rep0 - symbol - 1)
                                                        >= -1);
                                        assert((int32_t)(rep0 - symbol - 1)
                                                        <= 82);
                                        probs = coder->pos_special + rep0
                                                        - symbol - 1;
                                        symbol = 1;
                                        offset = 0;
        case SEQ_DIST_MODEL:
                                        do {
                                                rc_bit_safe(probs[symbol], ,
                                                        rep0 += 1U << offset,
                                                        SEQ_DIST_MODEL);
                                        } while (++offset < limit);
                                } else {
                                        assert(symbol >= 14);
                                        assert(limit >= 6);
                                        limit -= ALIGN_BITS;
                                        assert(limit >= 2);
        case SEQ_DIRECT:
                                        rc_direct_safe(rep0, limit,
                                                        SEQ_DIRECT);

                                        rep0 <<= ALIGN_BITS;
                                        symbol = 0;
                                        offset = 1;
        case SEQ_ALIGN:
                                        do {
                                                rc_bit_last_safe(
                                                        coder->pos_align[
                                                                offset
                                                                + symbol],
                                                        ,
                                                        symbol += offset,
                                                        SEQ_ALIGN);
                                                offset <<= 1;
                                        } while (offset < ALIGN_SIZE);

                                        rep0 += symbol;

                                        if (rep0 == UINT32_MAX) {
                                                // End of payload marker was
                                                // found. It may only be
                                                // present if
                                                //   - uncompressed size is
                                                //     unknown or
                                                //   - after known uncompressed
                                                //     size amount of bytes has
                                                //     been decompressed and
                                                //     caller has indicated
                                                //     that EOPM might be used
                                                //     (it's not allowed in
                                                //     LZMA2).
#ifndef HAVE_SMALL
eopm:
#endif
                                                if (!eopm_is_valid) {
                                                        ret = LZMA_DATA_ERROR;
                                                        goto out;
                                                }

        case SEQ_EOPM:
                                                // LZMA1 stream with
                                                // end-of-payload marker.
                                                rc_normalize_safe(SEQ_EOPM);
                                                ret = rc_is_finished(rc)
                                                        ? LZMA_STREAM_END
                                                        : LZMA_DATA_ERROR;
                                                goto out;
                                        }
                                }
                        }

                        if (unlikely(!dict_is_distance_valid(&dict, rep0))) {
                                ret = LZMA_DATA_ERROR;
                                goto out;
                        }

                } else {
                        /////////////////////
                        // Repeated match. //
                        /////////////////////

                        rc_update_1(coder->is_rep[state]);

                        if (unlikely(!dict_is_distance_valid(&dict, 0))) {
                                ret = LZMA_DATA_ERROR;
                                goto out;
                        }

        case SEQ_IS_REP0:
                        rc_if_0_safe(coder->is_rep0[state], SEQ_IS_REP0) {
                                rc_update_0(coder->is_rep0[state]);

        case SEQ_IS_REP0_LONG:
                                rc_if_0_safe(coder->is_rep0_long
                                                [state][pos_state],
                                                SEQ_IS_REP0_LONG) {
                                        rc_update_0(coder->is_rep0_long[
                                                        state][pos_state]);

                                        update_short_rep(state);

        case SEQ_SHORTREP:
                                        if (dict_put_safe(&dict,
                                                        dict_get(&dict,
                                                        rep0))) {
                                                coder->sequence = SEQ_SHORTREP;
                                                goto out;
                                        }

                                        continue;
                                }

                                rc_update_1(coder->is_rep0_long[
                                                state][pos_state]);

                        } else {
                                rc_update_1(coder->is_rep0[state]);

        case SEQ_IS_REP1:
                                rc_if_0_safe(coder->is_rep1[state], SEQ_IS_REP1) {
                                        rc_update_0(coder->is_rep1[state]);

                                        const uint32_t distance = rep1;
                                        rep1 = rep0;
                                        rep0 = distance;

                                } else {
                                        rc_update_1(coder->is_rep1[state]);
        case SEQ_IS_REP2:
                                        rc_if_0_safe(coder->is_rep2[state],
                                                        SEQ_IS_REP2) {
                                                rc_update_0(coder->is_rep2[
                                                                state]);

                                                const uint32_t distance = rep2;
                                                rep2 = rep1;
                                                rep1 = rep0;
                                                rep0 = distance;

                                        } else {
                                                rc_update_1(coder->is_rep2[
                                                                state]);

                                                const uint32_t distance = rep3;
                                                rep3 = rep2;
                                                rep2 = rep1;
                                                rep1 = rep0;
                                                rep0 = distance;
                                        }
                                }
                        }

                        update_long_rep(state);

                        len_decode(len, coder->rep_len_decoder,
                                        pos_state, SEQ_REP_LEN);
                }

                /////////////////////////////////
                // Repeat from history buffer. //
                /////////////////////////////////

                assert(len >= MATCH_LEN_MIN);
                assert(len <= MATCH_LEN_MAX);

        case SEQ_COPY:
                if (unlikely(dict_repeat(&dict, rep0, &len))) {
                        coder->sequence = SEQ_COPY;
                        goto out;
                }
        }

out:
        // Save state

        // NOTE: Must not copy dict.limit.
        dictptr->pos = dict.pos;
        dictptr->full = dict.full;

        rc_from_local(coder->rc, *in_pos);

        coder->state = state;
        coder->rep0 = rep0;
        coder->rep1 = rep1;
        coder->rep2 = rep2;
        coder->rep3 = rep3;

        coder->probs = probs;
        coder->symbol = symbol;
        coder->limit = limit;
        coder->offset = offset;
        coder->len = len;

        // Update the remaining amount of uncompressed data if uncompressed
        // size was known.
        if (coder->uncompressed_size != LZMA_VLI_UNKNOWN) {
                coder->uncompressed_size -= dict.pos - dict_start;

                // If we have gotten all the output but the decoder wants
                // to write more output, the file is corrupt. There are
                // three SEQ values where output is produced.
                if (coder->uncompressed_size == 0 && ret == LZMA_OK
                                && (coder->sequence == SEQ_LITERAL_WRITE
                                        || coder->sequence == SEQ_SHORTREP
                                        || coder->sequence == SEQ_COPY))
                        ret = LZMA_DATA_ERROR;
        }

        if (ret == LZMA_STREAM_END) {
                // Reset the range decoder so that it is ready to reinitialize
                // for a new LZMA2 chunk.
                rc_reset(coder->rc);
                coder->sequence = SEQ_IS_MATCH;
        }

        return ret;
}


static void
lzma_decoder_uncompressed(void *coder_ptr, lzma_vli uncompressed_size,
                bool allow_eopm)
{
        lzma_lzma1_decoder *coder = coder_ptr;
        coder->uncompressed_size = uncompressed_size;
        coder->allow_eopm = allow_eopm;
}


static void
lzma_decoder_reset(void *coder_ptr, const void *opt)
{
        lzma_lzma1_decoder *coder = coder_ptr;
        const lzma_options_lzma *options = opt;

        // NOTE: We assume that lc/lp/pb are valid since they were
        // successfully decoded with lzma_lzma_decode_properties().

        // Calculate pos_mask. We don't need pos_bits as is for anything.
        coder->pos_mask = (1U << options->pb) - 1;

        // Initialize the literal decoder.
        literal_init(coder->literal, options->lc, options->lp);

        coder->literal_context_bits = options->lc;
        coder->literal_mask = literal_mask_calc(options->lc, options->lp);

        // State
        coder->state = STATE_LIT_LIT;
        coder->rep0 = 0;
        coder->rep1 = 0;
        coder->rep2 = 0;
        coder->rep3 = 0;
        coder->pos_mask = (1U << options->pb) - 1;

        // Range decoder
        rc_reset(coder->rc);

        // Bit and bittree decoders
        for (uint32_t i = 0; i < STATES; ++i) {
                for (uint32_t j = 0; j <= coder->pos_mask; ++j) {
                        bit_reset(coder->is_match[i][j]);
                        bit_reset(coder->is_rep0_long[i][j]);
                }

                bit_reset(coder->is_rep[i]);
                bit_reset(coder->is_rep0[i]);
                bit_reset(coder->is_rep1[i]);
                bit_reset(coder->is_rep2[i]);
        }

        for (uint32_t i = 0; i < DIST_STATES; ++i)
                bittree_reset(coder->dist_slot[i], DIST_SLOT_BITS);

        for (uint32_t i = 0; i < FULL_DISTANCES - DIST_MODEL_END; ++i)
                bit_reset(coder->pos_special[i]);

        bittree_reset(coder->pos_align, ALIGN_BITS);

        // Len decoders (also bit/bittree)
        const uint32_t num_pos_states = 1U << options->pb;
        bit_reset(coder->match_len_decoder.choice);
        bit_reset(coder->match_len_decoder.choice2);
        bit_reset(coder->rep_len_decoder.choice);
        bit_reset(coder->rep_len_decoder.choice2);

        for (uint32_t pos_state = 0; pos_state < num_pos_states; ++pos_state) {
                bittree_reset(coder->match_len_decoder.low[pos_state],
                                LEN_LOW_BITS);
                bittree_reset(coder->match_len_decoder.mid[pos_state],
                                LEN_MID_BITS);

                bittree_reset(coder->rep_len_decoder.low[pos_state],
                                LEN_LOW_BITS);
                bittree_reset(coder->rep_len_decoder.mid[pos_state],
                                LEN_MID_BITS);
        }

        bittree_reset(coder->match_len_decoder.high, LEN_HIGH_BITS);
        bittree_reset(coder->rep_len_decoder.high, LEN_HIGH_BITS);

        coder->sequence = SEQ_IS_MATCH;
        coder->probs = NULL;
        coder->symbol = 0;
        coder->limit = 0;
        coder->offset = 0;
        coder->len = 0;

        return;
}


extern lzma_ret
lzma_lzma_decoder_create(lzma_lz_decoder *lz, const lzma_allocator *allocator,
                const lzma_options_lzma *options, lzma_lz_options *lz_options)
{
        if (lz->coder == NULL) {
                lz->coder = lzma_alloc(sizeof(lzma_lzma1_decoder), allocator);
                if (lz->coder == NULL)
                        return LZMA_MEM_ERROR;

                lz->code = &lzma_decode;
                lz->reset = &lzma_decoder_reset;
                lz->set_uncompressed = &lzma_decoder_uncompressed;
        }

        // All dictionary sizes are OK here. LZ decoder will take care of
        // the special cases.
        lz_options->dict_size = options->dict_size;
        lz_options->preset_dict = options->preset_dict;
        lz_options->preset_dict_size = options->preset_dict_size;

        return LZMA_OK;
}


/// Allocate and initialize LZMA decoder. This is used only via LZ
/// initialization (lzma_lzma_decoder_init() passes function pointer to
/// the LZ initialization).
static lzma_ret
lzma_decoder_init(lzma_lz_decoder *lz, const lzma_allocator *allocator,
                lzma_vli id, const void *options, lzma_lz_options *lz_options)
{
        if (!is_lclppb_valid(options))
                return LZMA_PROG_ERROR;

        lzma_vli uncomp_size = LZMA_VLI_UNKNOWN;
        bool allow_eopm = true;

        if (id == LZMA_FILTER_LZMA1EXT) {
                const lzma_options_lzma *opt = options;

                // Only one flag is supported.
                if (opt->ext_flags & ~LZMA_LZMA1EXT_ALLOW_EOPM)
                        return LZMA_OPTIONS_ERROR;

                // FIXME? Using lzma_vli instead of uint64_t is weird because
                // this has nothing to do with .xz headers and variable-length
                // integer encoding. On the other hand, using LZMA_VLI_UNKNOWN
                // instead of UINT64_MAX is clearer when unknown size is
                // meant. A problem with using lzma_vli is that now we
                // allow > LZMA_VLI_MAX which is fine in this file but
                // it's still confusing. Note that alone_decoder.c also
                // allows > LZMA_VLI_MAX when setting uncompressed size.
                uncomp_size = opt->ext_size_low
                                + ((uint64_t)(opt->ext_size_high) << 32);
                allow_eopm = (opt->ext_flags & LZMA_LZMA1EXT_ALLOW_EOPM) != 0
                                || uncomp_size == LZMA_VLI_UNKNOWN;
        }

        return_if_error(lzma_lzma_decoder_create(
                        lz, allocator, options, lz_options));

        lzma_decoder_reset(lz->coder, options);
        lzma_decoder_uncompressed(lz->coder, uncomp_size, allow_eopm);

        return LZMA_OK;
}


extern lzma_ret
lzma_lzma_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
                const lzma_filter_info *filters)
{
        // LZMA can only be the last filter in the chain. This is enforced
        // by the raw_decoder initialization.
        assert(filters[1].init == NULL);

        return lzma_lz_decoder_init(next, allocator, filters,
                        &lzma_decoder_init);
}


extern bool
lzma_lzma_lclppb_decode(lzma_options_lzma *options, uint8_t byte)
{
        if (byte > (4 * 5 + 4) * 9 + 8)
                return true;

        // See the file format specification to understand this.
        options->pb = byte / (9 * 5);
        byte -= options->pb * 9 * 5;
        options->lp = byte / 9;
        options->lc = byte - options->lp * 9;

        return options->lc + options->lp > LZMA_LCLP_MAX;
}


extern uint64_t
lzma_lzma_decoder_memusage_nocheck(const void *options)
{
        const lzma_options_lzma *const opt = options;
        return sizeof(lzma_lzma1_decoder)
                        + lzma_lz_decoder_memusage(opt->dict_size);
}


extern uint64_t
lzma_lzma_decoder_memusage(const void *options)
{
        if (!is_lclppb_valid(options))
                return UINT64_MAX;

        return lzma_lzma_decoder_memusage_nocheck(options);
}


extern lzma_ret
lzma_lzma_props_decode(void **options, const lzma_allocator *allocator,
                const uint8_t *props, size_t props_size)
{
        if (props_size != 5)
                return LZMA_OPTIONS_ERROR;

        lzma_options_lzma *opt
                        = lzma_alloc(sizeof(lzma_options_lzma), allocator);
        if (opt == NULL)
                return LZMA_MEM_ERROR;

        if (lzma_lzma_lclppb_decode(opt, props[0]))
                goto error;

        // All dictionary sizes are accepted, including zero. LZ decoder
        // will automatically use a dictionary at least a few KiB even if
        // a smaller dictionary is requested.
        opt->dict_size = read32le(props + 1);

        opt->preset_dict = NULL;
        opt->preset_dict_size = 0;

        *options = opt;

        return LZMA_OK;

error:
        lzma_free(opt, allocator);
        return LZMA_OPTIONS_ERROR;
}