/*
 * .xz Stream decoder
 *
 * Author: Lasse Collin <lasse.collin@tukaani.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_stream.h"

/* Hash used to validate the Index field */
struct xz_dec_hash {
        vli_type unpadded;
        vli_type uncompressed;
        uint32_t crc32;
};

struct xz_dec {
        /* Position in dec_main() */
        enum {
                SEQ_STREAM_HEADER,
                SEQ_BLOCK_START,
                SEQ_BLOCK_HEADER,
                SEQ_BLOCK_UNCOMPRESS,
                SEQ_BLOCK_PADDING,
                SEQ_BLOCK_CHECK,
                SEQ_INDEX,
                SEQ_INDEX_PADDING,
                SEQ_INDEX_CRC32,
                SEQ_STREAM_FOOTER
        } sequence;

        /* Position in variable-length integers and Check fields */
        uint32_t pos;

        /* Variable-length integer decoded by dec_vli() */
        vli_type vli;

        /* Saved in_pos and out_pos */
        size_t in_start;
        size_t out_start;

        /* CRC32 value in Block or Index */
        uint32_t crc32;

        /* Type of the integrity check calculated from uncompressed data */
        enum xz_check check_type;

        /* Operation mode */
        enum xz_mode mode;

        /*
         * True if the next call to xz_dec_run() is allowed to return
         * XZ_BUF_ERROR.
         */
        bool allow_buf_error;

        /* Information stored in Block Header */
        struct {
                /*
                 * Value stored in the Compressed Size field, or
                 * VLI_UNKNOWN if Compressed Size is not present.
                 */
                vli_type compressed;

                /*
                 * Value stored in the Uncompressed Size field, or
                 * VLI_UNKNOWN if Uncompressed Size is not present.
                 */
                vli_type uncompressed;

                /* Size of the Block Header field */
                uint32_t size;
        } block_header;

        /* Information collected when decoding Blocks */
        struct {
                /* Observed compressed size of the current Block */
                vli_type compressed;

                /* Observed uncompressed size of the current Block */
                vli_type uncompressed;

                /* Number of Blocks decoded so far */
                vli_type count;

                /*
                 * Hash calculated from the Block sizes. This is used to
                 * validate the Index field.
                 */
                struct xz_dec_hash hash;
        } block;

        /* Variables needed when verifying the Index field */
        struct {
                /* Position in dec_index() */
                enum {
                        SEQ_INDEX_COUNT,
                        SEQ_INDEX_UNPADDED,
                        SEQ_INDEX_UNCOMPRESSED
                } sequence;

                /* Size of the Index in bytes */
                vli_type size;

                /* Number of Records (matches block.count in valid files) */
                vli_type count;

                /*
                 * Hash calculated from the Records (matches block.hash in
                 * valid files).
                 */
                struct xz_dec_hash hash;
        } index;

        /*
         * Temporary buffer needed to hold Stream Header, Block Header,
         * and Stream Footer. The Block Header is the biggest (1 KiB)
         * so we reserve space according to that. buf[] has to be aligned
         * to a multiple of four bytes; the size_t variables before it
         * should guarantee this.
         */
        struct {
                size_t pos;
                size_t size;
                uint8_t buf[1024];
        } temp;

        struct xz_dec_lzma2 *lzma2;

#ifdef XZ_DEC_BCJ
        struct xz_dec_bcj *bcj;
        bool bcj_active;
#endif
};

#ifdef XZ_DEC_ANY_CHECK
/* Sizes of the Check field with different Check IDs */
static const uint8_t check_sizes[16] = {
        0,
        4, 4, 4,
        8, 8, 8,
        16, 16, 16,
        32, 32, 32,
        64, 64, 64
};
#endif

/*
 * Fill s->temp by copying data starting from b->in[b->in_pos]. Caller
 * must have set s->temp.pos to indicate how much data we are supposed
 * to copy into s->temp.buf. Return true once s->temp.pos has reached
 * s->temp.size.
 */
static bool XZ_FUNC fill_temp(struct xz_dec *s, struct xz_buf *b)
{
        size_t copy_size = min_t(size_t,
                        b->in_size - b->in_pos, s->temp.size - s->temp.pos);

        memcpy(s->temp.buf + s->temp.pos, b->in + b->in_pos, copy_size);
        b->in_pos += copy_size;
        s->temp.pos += copy_size;

        if (s->temp.pos == s->temp.size) {
                s->temp.pos = 0;
                return true;
        }

        return false;
}

/* Decode a variable-length integer (little-endian base-128 encoding) */
static enum xz_ret XZ_FUNC dec_vli(struct xz_dec *s,
                const uint8_t *in, size_t *in_pos, size_t in_size)
{
        uint8_t byte;

        if (s->pos == 0)
                s->vli = 0;

        while (*in_pos < in_size) {
                byte = in[*in_pos];
                ++*in_pos;

                s->vli |= (vli_type)(byte & 0x7F) << s->pos;

                if ((byte & 0x80) == 0) {
                        /* Don't allow non-minimal encodings. */
                        if (byte == 0 && s->pos != 0)
                                return XZ_DATA_ERROR;

                        s->pos = 0;
                        return XZ_STREAM_END;
                }

                s->pos += 7;
                if (s->pos == 7 * VLI_BYTES_MAX)
                        return XZ_DATA_ERROR;
        }

        return XZ_OK;
}

/*
 * Decode the Compressed Data field from a Block. Update and validate
 * the observed compressed and uncompressed sizes of the Block so that
 * they don't exceed the values possibly stored in the Block Header
 * (validation assumes that no integer overflow occurs, since vli_type
 * is normally uint64_t). Update the CRC32 if presence of the CRC32
 * field was indicated in Stream Header.
 *
 * Once the decoding is finished, validate that the observed sizes match
 * the sizes possibly stored in the Block Header. Update the hash and
 * Block count, which are later used to validate the Index field.
 */
static enum xz_ret XZ_FUNC dec_block(struct xz_dec *s, struct xz_buf *b)
{
        enum xz_ret ret;

        s->in_start = b->in_pos;
        s->out_start = b->out_pos;

#ifdef XZ_DEC_BCJ
        if (s->bcj_active)
                ret = xz_dec_bcj_run(s->bcj, s->lzma2, b);
        else
#endif
                ret = xz_dec_lzma2_run(s->lzma2, b);

        s->block.compressed += b->in_pos - s->in_start;
        s->block.uncompressed += b->out_pos - s->out_start;

        /*
         * There is no need to separately check for VLI_UNKNOWN, since
         * the observed sizes are always smaller than VLI_UNKNOWN.
         */
        if (s->block.compressed > s->block_header.compressed
                        || s->block.uncompressed
                                > s->block_header.uncompressed)
                return XZ_DATA_ERROR;

        if (s->check_type == XZ_CHECK_CRC32)
                s->crc32 = xz_crc32(b->out + s->out_start,
                                b->out_pos - s->out_start, s->crc32);

        if (ret == XZ_STREAM_END) {
                if (s->block_header.compressed != VLI_UNKNOWN
                                && s->block_header.compressed
                                        != s->block.compressed)
                        return XZ_DATA_ERROR;

                if (s->block_header.uncompressed != VLI_UNKNOWN
                                && s->block_header.uncompressed
                                        != s->block.uncompressed)
                        return XZ_DATA_ERROR;

                s->block.hash.unpadded += s->block_header.size
                                + s->block.compressed;

#ifdef XZ_DEC_ANY_CHECK
                s->block.hash.unpadded += check_sizes[s->check_type];
#else
                if (s->check_type == XZ_CHECK_CRC32)
                        s->block.hash.unpadded += 4;
#endif

                s->block.hash.uncompressed += s->block.uncompressed;
                s->block.hash.crc32 = xz_crc32(
                                (const uint8_t *)&s->block.hash,
                                sizeof(s->block.hash), s->block.hash.crc32);

                ++s->block.count;
        }

        return ret;
}

/* Update the Index size and the CRC32 value. */
static void XZ_FUNC index_update(struct xz_dec *s, const struct xz_buf *b)
{
        size_t in_used = b->in_pos - s->in_start;
        s->index.size += in_used;
        s->crc32 = xz_crc32(b->in + s->in_start, in_used, s->crc32);
}

/*
 * Decode the Number of Records, Unpadded Size, and Uncompressed Size
 * fields from the Index field. That is, Index Padding and CRC32 are not
 * decoded by this function.
 *
 * This can return XZ_OK (more input needed), XZ_STREAM_END (everything
 * successfully decoded), or XZ_DATA_ERROR (input is corrupt).
 */
static enum xz_ret XZ_FUNC dec_index(struct xz_dec *s, struct xz_buf *b)
{
        enum xz_ret ret;

        do {
                ret = dec_vli(s, b->in, &b->in_pos, b->in_size);
                if (ret != XZ_STREAM_END) {
                        index_update(s, b);
                        return ret;
                }

                switch (s->index.sequence) {
                case SEQ_INDEX_COUNT:
                        s->index.count = s->vli;

                        /*
                         * Validate that the Number of Records field
                         * indicates the same number of Records as
                         * there were Blocks in the Stream.
                         */
                        if (s->index.count != s->block.count)
                                return XZ_DATA_ERROR;

                        s->index.sequence = SEQ_INDEX_UNPADDED;
                        break;

                case SEQ_INDEX_UNPADDED:
                        s->index.hash.unpadded += s->vli;
                        s->index.sequence = SEQ_INDEX_UNCOMPRESSED;
                        break;

                case SEQ_INDEX_UNCOMPRESSED:
                        s->index.hash.uncompressed += s->vli;
                        s->index.hash.crc32 = xz_crc32(
                                        (const uint8_t *)&s->index.hash,
                                        sizeof(s->index.hash),
                                        s->index.hash.crc32);
                        --s->index.count;
                        s->index.sequence = SEQ_INDEX_UNPADDED;
                        break;
                }
        } while (s->index.count > 0);

        return XZ_STREAM_END;
}

/*
 * Validate that the next four input bytes match the value of s->crc32.
 * s->pos must be zero when starting to validate the first byte.
 */
static enum xz_ret XZ_FUNC crc32_validate(struct xz_dec *s, struct xz_buf *b)
{
        do {
                if (b->in_pos == b->in_size)
                        return XZ_OK;

                if (((s->crc32 >> s->pos) & 0xFF) != b->in[b->in_pos++])
                        return XZ_DATA_ERROR;

                s->pos += 8;
        } while (s->pos < 32);

        s->crc32 = 0;
        s->pos = 0;

        return XZ_STREAM_END;
}

#ifdef XZ_DEC_ANY_CHECK
/*
 * Skip over the Check field when the Check ID is not supported.
 * Returns true once the whole Check field has been skipped over.
 */
static bool XZ_FUNC check_skip(struct xz_dec *s, struct xz_buf *b)
{
        while (s->pos < check_sizes[s->check_type]) {
                if (b->in_pos == b->in_size)
                        return false;

                ++b->in_pos;
                ++s->pos;
        }

        s->pos = 0;

        return true;
}
#endif

/* Decode the Stream Header field (the first 12 bytes of the .xz Stream). */
static enum xz_ret XZ_FUNC dec_stream_header(struct xz_dec *s)
{
        if (!memeq(s->temp.buf, HEADER_MAGIC, HEADER_MAGIC_SIZE))
                return XZ_FORMAT_ERROR;

        if (xz_crc32(s->temp.buf + HEADER_MAGIC_SIZE, 2, 0)
                        != get_le32(s->temp.buf + HEADER_MAGIC_SIZE + 2))
                return XZ_DATA_ERROR;

        if (s->temp.buf[HEADER_MAGIC_SIZE] != 0)
                return XZ_OPTIONS_ERROR;

        /*
         * Of integrity checks, we support only none (Check ID = 0) and
         * CRC32 (Check ID = 1). However, if XZ_DEC_ANY_CHECK is defined,
         * we will accept other check types too, but then the check won't
         * be verified and a warning (XZ_UNSUPPORTED_CHECK) will be given.
         */
        s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];

#ifdef XZ_DEC_ANY_CHECK
        if (s->check_type > XZ_CHECK_MAX)
                return XZ_OPTIONS_ERROR;

        if (s->check_type > XZ_CHECK_CRC32)
                return XZ_UNSUPPORTED_CHECK;
#else
        if (s->check_type > XZ_CHECK_CRC32)
                return XZ_OPTIONS_ERROR;
#endif

        return XZ_OK;
}

/* Decode the Stream Footer field (the last 12 bytes of the .xz Stream) */
static enum xz_ret XZ_FUNC dec_stream_footer(struct xz_dec *s)
{
        if (!memeq(s->temp.buf + 10, FOOTER_MAGIC, FOOTER_MAGIC_SIZE))
                return XZ_DATA_ERROR;

        if (xz_crc32(s->temp.buf + 4, 6, 0) != get_le32(s->temp.buf))
                return XZ_DATA_ERROR;

        /*
         * Validate Backward Size. Note that we never added the size of the
         * Index CRC32 field to s->index.size, thus we use s->index.size / 4
         * instead of s->index.size / 4 - 1.
         */
        if ((s->index.size >> 2) != get_le32(s->temp.buf + 4))
                return XZ_DATA_ERROR;

        if (s->temp.buf[8] != 0 || s->temp.buf[9] != s->check_type)
                return XZ_DATA_ERROR;

        /*
         * Use XZ_STREAM_END instead of XZ_OK to be more convenient
         * for the caller.
         */
        return XZ_STREAM_END;
}

/* Decode the Block Header and initialize the filter chain. */
static enum xz_ret XZ_FUNC dec_block_header(struct xz_dec *s)
{
        enum xz_ret ret;

        /*
         * Validate the CRC32. We know that the temp buffer is at least
         * eight bytes so this is safe.
         */
        s->temp.size -= 4;
        if (xz_crc32(s->temp.buf, s->temp.size, 0)
                        != get_le32(s->temp.buf + s->temp.size))
                return XZ_DATA_ERROR;

        s->temp.pos = 2;

        /*
         * Catch unsupported Block Flags. We support only one or two filters
         * in the chain, so we catch that with the same test.
         */
#ifdef XZ_DEC_BCJ
        if (s->temp.buf[1] & 0x3E)
#else
        if (s->temp.buf[1] & 0x3F)
#endif
                return XZ_OPTIONS_ERROR;

        /* Compressed Size */
        if (s->temp.buf[1] & 0x40) {
                if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
                                        != XZ_STREAM_END)
                        return XZ_DATA_ERROR;

                s->block_header.compressed = s->vli;
        } else {
                s->block_header.compressed = VLI_UNKNOWN;
        }

        /* Uncompressed Size */
        if (s->temp.buf[1] & 0x80) {
                if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
                                != XZ_STREAM_END)
                        return XZ_DATA_ERROR;

                s->block_header.uncompressed = s->vli;
        } else {
                s->block_header.uncompressed = VLI_UNKNOWN;
        }

#ifdef XZ_DEC_BCJ
        /* If there are two filters, the first one must be a BCJ filter. */
        s->bcj_active = s->temp.buf[1] & 0x01;
        if (s->bcj_active) {
                if (s->temp.size - s->temp.pos < 2)
                        return XZ_OPTIONS_ERROR;

                ret = xz_dec_bcj_reset(s->bcj, s->temp.buf[s->temp.pos++]);
                if (ret != XZ_OK)
                        return ret;

                /*
                 * We don't support custom start offset,
                 * so Size of Properties must be zero.
                 */
                if (s->temp.buf[s->temp.pos++] != 0x00)
                        return XZ_OPTIONS_ERROR;
        }
#endif

        /* Valid Filter Flags always take at least two bytes. */
        if (s->temp.size - s->temp.pos < 2)
                return XZ_DATA_ERROR;

        /* Filter ID = LZMA2 */
        if (s->temp.buf[s->temp.pos++] != 0x21)
                return XZ_OPTIONS_ERROR;

        /* Size of Properties = 1-byte Filter Properties */
        if (s->temp.buf[s->temp.pos++] != 0x01)
                return XZ_OPTIONS_ERROR;

        /* Filter Properties contains LZMA2 dictionary size. */
        if (s->temp.size - s->temp.pos < 1)
                return XZ_DATA_ERROR;

        ret = xz_dec_lzma2_reset(s->lzma2, s->temp.buf[s->temp.pos++]);
        if (ret != XZ_OK)
                return ret;

        /* The rest must be Header Padding. */
        while (s->temp.pos < s->temp.size)
                if (s->temp.buf[s->temp.pos++] != 0x00)
                        return XZ_OPTIONS_ERROR;

        s->temp.pos = 0;
        s->block.compressed = 0;
        s->block.uncompressed = 0;

        return XZ_OK;
}

static NOINLINE enum xz_ret XZ_FUNC dec_main(struct xz_dec *s, struct xz_buf *b)
{
        enum xz_ret ret;

        /*
         * Store the start position for the case when we are in the middle
         * of the Index field.
         */
        s->in_start = b->in_pos;

        while (true) {
                switch (s->sequence) {
                case SEQ_STREAM_HEADER:
                        /*
                         * Stream Header is copied to s->temp, and then
                         * decoded from there. This way if the caller
                         * gives us only little input at a time, we can
                         * still keep the Stream Header decoding code
                         * simple. Similar approach is used in many places
                         * in this file.
                         */
                        if (!fill_temp(s, b))
                                return XZ_OK;

                        /*
                         * If dec_stream_header() returns
                         * XZ_UNSUPPORTED_CHECK, it is still possible
                         * to continue decoding if working in multi-call
                         * mode. Thus, update s->sequence before calling
                         * dec_stream_header().
                         */
                        s->sequence = SEQ_BLOCK_START;

                        ret = dec_stream_header(s);
                        if (ret != XZ_OK)
                                return ret;

                case SEQ_BLOCK_START:
                        /* We need one byte of input to continue. */
                        if (b->in_pos == b->in_size)
                                return XZ_OK;

                        /* See if this is the beginning of the Index field. */
                        if (b->in[b->in_pos] == 0) {
                                s->in_start = b->in_pos++;
                                s->sequence = SEQ_INDEX;
                                break;
                        }

                        /*
                         * Calculate the size of the Block Header and
                         * prepare to decode it.
                         */
                        s->block_header.size
                                = ((uint32_t)b->in[b->in_pos] + 1) * 4;

                        s->temp.size = s->block_header.size;
                        s->temp.pos = 0;
                        s->sequence = SEQ_BLOCK_HEADER;

                case SEQ_BLOCK_HEADER:
                        if (!fill_temp(s, b))
                                return XZ_OK;

                        ret = dec_block_header(s);
                        if (ret != XZ_OK)
                                return ret;

                        s->sequence = SEQ_BLOCK_UNCOMPRESS;

                case SEQ_BLOCK_UNCOMPRESS:
                        ret = dec_block(s, b);
                        if (ret != XZ_STREAM_END)
                                return ret;

                        s->sequence = SEQ_BLOCK_PADDING;

                case SEQ_BLOCK_PADDING:
                        /*
                         * Size of Compressed Data + Block Padding
                         * must be a multiple of four. We don't need
                         * s->block.compressed for anything else
                         * anymore, so we use it here to test the size
                         * of the Block Padding field.
                         */
                        while (s->block.compressed & 3) {
                                if (b->in_pos == b->in_size)
                                        return XZ_OK;

                                if (b->in[b->in_pos++] != 0)
                                        return XZ_DATA_ERROR;

                                ++s->block.compressed;
                        }

                        s->sequence = SEQ_BLOCK_CHECK;

                case SEQ_BLOCK_CHECK:
                        if (s->check_type == XZ_CHECK_CRC32) {
                                ret = crc32_validate(s, b);
                                if (ret != XZ_STREAM_END)
                                        return ret;
                        }
#ifdef XZ_DEC_ANY_CHECK
                        else if (!check_skip(s, b)) {
                                return XZ_OK;
                        }
#endif

                        s->sequence = SEQ_BLOCK_START;
                        break;

                case SEQ_INDEX:
                        ret = dec_index(s, b);
                        if (ret != XZ_STREAM_END)
                                return ret;

                        s->sequence = SEQ_INDEX_PADDING;

                case SEQ_INDEX_PADDING:
                        while ((s->index.size + (b->in_pos - s->in_start))
                                        & 3) {
                                if (b->in_pos == b->in_size) {
                                        index_update(s, b);
                                        return XZ_OK;
                                }

                                if (b->in[b->in_pos++] != 0)
                                        return XZ_DATA_ERROR;
                        }

                        /* Finish the CRC32 value and Index size. */
                        index_update(s, b);

                        /* Compare the hashes to validate the Index field. */
                        if (!memeq(&s->block.hash, &s->index.hash,
                                        sizeof(s->block.hash)))
                                return XZ_DATA_ERROR;

                        s->sequence = SEQ_INDEX_CRC32;

                case SEQ_INDEX_CRC32:
                        ret = crc32_validate(s, b);
                        if (ret != XZ_STREAM_END)
                                return ret;

                        s->temp.size = STREAM_HEADER_SIZE;
                        s->sequence = SEQ_STREAM_FOOTER;

                case SEQ_STREAM_FOOTER:
                        if (!fill_temp(s, b))
                                return XZ_OK;

                        return dec_stream_footer(s);
                }
        }

        /* Never reached */
}

/*
 * xz_dec_run() is a wrapper for dec_main() to handle some special cases in
 * multi-call and single-call decoding.
 *
 * In multi-call mode, we must return XZ_BUF_ERROR when it seems clear that we
 * are not going to make any progress anymore. This is to prevent the caller
 * from calling us infinitely when the input file is truncated or otherwise
 * corrupt. Since zlib-style API allows that the caller fills the input buffer
 * only when the decoder doesn't produce any new output, we have to be careful
 * to avoid returning XZ_BUF_ERROR too easily: XZ_BUF_ERROR is returned only
 * after the second consecutive call to xz_dec_run() that makes no progress.
 *
 * In single-call mode, if we couldn't decode everything and no error
 * occurred, either the input is truncated or the output buffer is too small.
 * Since we know that the last input byte never produces any output, we know
 * that if all the input was consumed and decoding wasn't finished, the file
 * must be corrupt. Otherwise the output buffer has to be too small or the
 * file is corrupt in a way that decoding it produces too big output.
 *
 * If single-call decoding fails, we reset b->in_pos and b->out_pos back to
 * their original values. This is because with some filter chains there won't
 * be any valid uncompressed data in the output buffer unless the decoding
 * actually succeeds (that's the price to pay of using the output buffer as
 * the workspace).
 */
XZ_EXTERN enum xz_ret XZ_FUNC xz_dec_run(struct xz_dec *s, struct xz_buf *b)
{
        size_t in_start;
        size_t out_start;
        enum xz_ret ret;

        if (DEC_IS_SINGLE(s->mode))
                xz_dec_reset(s);

        in_start = b->in_pos;
        out_start = b->out_pos;
        ret = dec_main(s, b);

        if (DEC_IS_SINGLE(s->mode)) {
                if (ret == XZ_OK)
                        ret = b->in_pos == b->in_size
                                        ? XZ_DATA_ERROR : XZ_BUF_ERROR;

                if (ret != XZ_STREAM_END) {
                        b->in_pos = in_start;
                        b->out_pos = out_start;
                }
        } else if (ret == XZ_OK && in_start == b->in_pos
                        && out_start == b->out_pos) {
                if (s->allow_buf_error)
                        ret = XZ_BUF_ERROR;

                s->allow_buf_error = true;
        } else {
                s->allow_buf_error = false;
        }

        return ret;
}

XZ_EXTERN struct xz_dec * XZ_FUNC xz_dec_init(
                enum xz_mode mode, uint32_t dict_max)
{
        struct xz_dec *s = kmalloc(sizeof(*s), GFP_KERNEL);
        if (s == NULL)
                return NULL;

        s->mode = mode;

#ifdef XZ_DEC_BCJ
        s->bcj = xz_dec_bcj_create(DEC_IS_SINGLE(mode));
        if (s->bcj == NULL)
                goto error_bcj;
#endif

        s->lzma2 = xz_dec_lzma2_create(mode, dict_max);
        if (s->lzma2 == NULL)
                goto error_lzma2;

        xz_dec_reset(s);
        return s;

error_lzma2:
#ifdef XZ_DEC_BCJ
        xz_dec_bcj_end(s->bcj);
error_bcj:
#endif
        kfree(s);
        return NULL;
}

XZ_EXTERN void XZ_FUNC xz_dec_reset(struct xz_dec *s)
{
        s->sequence = SEQ_STREAM_HEADER;
        s->allow_buf_error = false;
        s->pos = 0;
        s->crc32 = 0;
        memzero(&s->block, sizeof(s->block));
        memzero(&s->index, sizeof(s->index));
        s->temp.pos = 0;
        s->temp.size = STREAM_HEADER_SIZE;
}

XZ_EXTERN void XZ_FUNC xz_dec_end(struct xz_dec *s)
{
        if (s != NULL) {
                xz_dec_lzma2_end(s->lzma2);
#ifdef XZ_DEC_BCJ
                xz_dec_bcj_end(s->bcj);
#endif
                kfree(s);
        }
}