[wimlib] / src / lzx-decomp.c

/*
 * lzx-decomp.c
 *
 * Routines for LZX decompression.  The LZX format has many similarities to the
 * DEFLATE format used in zlib and gzip, but it's not quite the same.
 *
 */

/*
 * Copyright (C) 2012 Eric Biggers
 *
 * This file is part of wimlib, a library for working with WIM files.
 *
 * wimlib is free software; you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 2.1 of the License, or (at your option)
 * any later version.
 *
 * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with wimlib; if not, see http://www.gnu.org/licenses/.
 */

/* 
 * This file has been modified from code taken from cabextract v0.5, which was,
 * itself, a modified version of the lzx decompression code from unlzx.  The
 * code has been customized for wimlib.
 *
 * Some notes on the LZX compression format as used in Windows Imaging (WIM)
 * files:
 *
 * A compressed WIM file resource consists of a table of chunk offsets followed
 * by compressed chunks.  All compressed chunks except the last decompress to
 * WIM_CHUNK_SIZE (= 32768) bytes.  This is quite similar to the cabinet (.cab)
 * file format, but they are not the same (at least based on M$'s
 * documentation).  According to the documentation, in the cabinet format, the
 * LZX block size is independent from the CFDATA blocks and may span several
 * CFDATA blocks.  However, for WIM file resources, I have seen no case of a LZX
 * block spanning multiple WIM chunks.  This is probably done to make it easier
 * to randomly access the compressed file resources.  WIMLIB in fact makes use
 * of this feature to allow semi-random access to file resources in the
 * read_resource() function.
 *
 * Usually a WIM chunk will contain only one LZX block, but on rare occasions it
 * may contain multiple LZX block. The LZX block are usually the aligned block
 * type or verbatim block type, but can (very rarely) be the uncompressed block
 * type.  The size of a LZX block is specified by 1 or 17 bits following the 3
 * bits that specify the block type.  A '1' means to use the default block size
 * (equal to 32768), while a '0' means that the block size is given by the next
 * 16 bits.
 *
 * The cabinet format, as documented, allows for the possibility that a CFDATA
 * chunk is up to 6144 bytes larger than the uncompressed data.  In the WIM
 * format, however, it appears that every chunk that would be 32768 bytes or
 * more when compressed, is actually stored uncompressed.  This is not
 * documented by M$.
 *
 * The 'e8' preprocessing step that changes x86 call instructions to use
 * absolute offsets instead of relative offsets relies on a filesize parameter.
 * There is no such parameter for this in the WIM files (even though the size of
 * the file resource could be used for this purpose), and instead a magic file
 * size of 12000000 is used.  The 'e8' preprocessing is always done, and there
 * is no bit to indicate whether it is done or not.
 *
 */

/* 
 * Some more notes about errors in Microsoft's documentation:
 *
 * Microsoft's LZX document and their implementation of the com.ms.util.cab Java
 * package do not concur.
 *
 * In the LZX document, there is a table showing the correlation between window
 * size and the number of position slots. It states that the 1MB window = 40
 * slots and the 2MB window = 42 slots. In the implementation, 1MB = 42 slots,
 * 2MB = 50 slots. The actual calculation is 'find the first slot whose position
 * base is equal to or more than the required window size'. This would explain
 * why other tables in the document refer to 50 slots rather than 42.
 *
 * The constant NUM_PRIMARY_LENS used in the decompression pseudocode is not
 * defined in the specification.
 *
 * The LZX document states that aligned offset blocks have their aligned offset
 * huffman tree AFTER the main and length trees. The implementation suggests
 * that the aligned offset tree is BEFORE the main and length trees.
 *
 * The LZX document decoding algorithm states that, in an aligned offset block,
 * if an extra_bits value is 1, 2 or 3, then that number of bits should be read
 * and the result added to the match offset. This is correct for 1 and 2, but
 * not 3, where just a huffman symbol (using the aligned tree) should be read.
 *
 * Regarding the E8 preprocessing, the LZX document states 'No translation may
 * be performed on the last 6 bytes of the input block'. This is correct.
 * However, the pseudocode provided checks for the *E8 leader* up to the last 6
 * bytes. If the leader appears between -10 and -7 bytes from the end, this
 * would cause the next four bytes to be modified, at least one of which would
 * be in the last 6 bytes, which is not allowed according to the spec.
 *
 * The specification states that the huffman trees must always contain at least
 * one element. However, many CAB files contain blocks where the length tree is
 * completely empty (because there are no matches), and this is expected to
 * succeed.
 */

#include "util.h"
#include "lzx.h"

#include "decomp.h"

#include <string.h>

/* Huffman decoding tables and maps from symbols to code lengths. */
struct lzx_tables {

        u16 maintree_decode_table[(1 << LZX_MAINTREE_TABLEBITS) + 
                                        (LZX_MAINTREE_NUM_SYMBOLS * 2)];
        u8 maintree_lens[LZX_MAINTREE_NUM_SYMBOLS];


        u16 lentree_decode_table[(1 << LZX_LENTREE_TABLEBITS) + 
                                        (LZX_LENTREE_NUM_SYMBOLS * 2)];
        u8 lentree_lens[LZX_LENTREE_NUM_SYMBOLS];


        u16 alignedtree_decode_table[(1 << LZX_ALIGNEDTREE_TABLEBITS) + 
                                        (LZX_ALIGNEDTREE_NUM_SYMBOLS * 2)];
        u8 alignedtree_lens[LZX_ALIGNEDTREE_NUM_SYMBOLS];
};


/* 
 * Reads a Huffman-encoded symbol using the pre-tree. 
 */
static inline int read_huffsym_using_pretree(struct input_bitstream *istream, 
                                             const u16 pretree_decode_table[],
                                             const u8 pretree_lens[], uint *n)
{
        return read_huffsym(istream, pretree_decode_table, pretree_lens, 
                            LZX_PRETREE_NUM_SYMBOLS, LZX_PRETREE_TABLEBITS, n,
                            LZX_MAX_CODEWORD_LEN);
}

/* Reads a Huffman-encoded symbol using the main tree. */
static inline int read_huffsym_using_maintree(struct input_bitstream *istream, 
                                              const struct lzx_tables *tables, 
                                              uint *n)
{
        return read_huffsym(istream, tables->maintree_decode_table, 
                            tables->maintree_lens, LZX_MAINTREE_NUM_SYMBOLS,
                            LZX_MAINTREE_TABLEBITS, n, LZX_MAX_CODEWORD_LEN);
}

/* Reads a Huffman-encoded symbol using the length tree. */
static inline int read_huffsym_using_lentree(struct input_bitstream *istream, 
                                             const struct lzx_tables *tables, 
                                             uint *n)
{
        return read_huffsym(istream, tables->lentree_decode_table, 
                            tables->lentree_lens, LZX_LENTREE_NUM_SYMBOLS, 
                            LZX_LENTREE_TABLEBITS, n, LZX_MAX_CODEWORD_LEN);
}

/* Reads a Huffman-encoded symbol using the aligned offset tree. */
static inline int read_huffsym_using_alignedtree(struct input_bitstream *istream, 
                                                 const struct lzx_tables *tables, 
                                                 uint *n)
{
        return read_huffsym(istream, tables->alignedtree_decode_table, 
                            tables->alignedtree_lens,
                            LZX_ALIGNEDTREE_NUM_SYMBOLS, 
                            LZX_ALIGNEDTREE_TABLEBITS, n, 8);
}

/* 
 * Reads the pretree from the input, then uses the pretree to decode @num_lens
 * code length values from the input. 
 *
 * @istream:    The bit stream for the input.  It is positioned on the beginning
 *                      of the pretree for the code length values.
 * @lens:       An array that contains the length values from the previous time
 *                      the code lengths for this Huffman tree were read, or all
 *                      0's if this is the first time.  
 * @num_lens:   Number of length values to decode and return.
 *
 */
static int lzx_read_code_lens(struct input_bitstream *istream, u8 lens[], 
                              uint num_lens)
{
        /* Declare the decoding table and length table for the pretree. */
        u16 pretree_decode_table[(1 << LZX_PRETREE_TABLEBITS) + 
                                        (LZX_PRETREE_NUM_SYMBOLS * 2)];
        u8 pretree_lens[LZX_PRETREE_NUM_SYMBOLS];
        uint i;
        uint len;
        int ret;

        /* Read the code lengths of the pretree codes.  There are 20 lengths of
         * 4 bits each. */
        for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++) {
                ret = bitstream_read_bits(istream, LZX_PRETREE_ELEMENT_SIZE, 
                                          &len);
                if (ret != 0)
                        return ret;
                pretree_lens[i] = len;
        }

        /* Make the decoding table for the pretree. */
        ret = make_huffman_decode_table(pretree_decode_table, 
                                        LZX_PRETREE_NUM_SYMBOLS, 
                                        LZX_PRETREE_TABLEBITS, 
                                        pretree_lens, 
                                        LZX_MAX_CODEWORD_LEN);
        if (ret != 0)
                return ret;

        /* Pointer past the last length value that needs to be filled in. */
        u8 *lens_end = lens + num_lens;

        while (1) {

                /* Decode a symbol from the input.  If the symbol is between 0
                 * and 16, it is the difference from the old length.  If it is
                 * between 17 and 19, it is a special code that indicates that
                 * some number of the next lengths are all 0, or some number of
                 * the next lengths are all equal to the next symbol in the
                 * input. */
                uint tree_code;
                uint num_zeroes;
                uint code; 
                uint num_same;
                char value;

                ret = read_huffsym_using_pretree(istream, pretree_decode_table, 
                                                pretree_lens, &tree_code);
                if (ret != 0)
                        return ret;
                switch (tree_code) {
                case 17: /* Run of 0's */
                        ret = bitstream_read_bits(istream, 4, &num_zeroes);
                        if (ret != 0)
                                return ret;
                        num_zeroes += 4;
                        while (num_zeroes--) {
                                *lens = 0;
                                if (++lens == lens_end)
                                        return 0;
                        }
                        break;
                case 18: /* Longer run of 0's */
                        ret = bitstream_read_bits(istream, 5, &num_zeroes);
                        if (ret != 0)
                                return ret;
                        num_zeroes += 20;
                        while (num_zeroes--) {
                                *lens = 0;
                                if (++lens == lens_end)
                                        return 0;
                        }
                        break;
                case 19: /* Run of identical lengths */
                        ret = bitstream_read_bits(istream, 1, &num_same);
                        if (ret != 0)
                                return ret;
                        num_same += 4;

                        ret = read_huffsym_using_pretree(istream, 
                                                pretree_decode_table, 
                                                pretree_lens, &code);
                        if (ret != 0)
                                return ret;
                        value = (char)*lens - (char)code;
                        if (value < 0)
                                value += 17;
                        while (num_same--) {
                                *lens = value;
                                if (++lens == lens_end)
                                        return 0;
                        }
                        break;
                default: /* Difference from old length. */
                        value = (char)*lens - (char)tree_code;
                        if (value < 0)
                                value += 17;
                        *lens = value;
                        if (++lens == lens_end)
                                return 0;
                        break;
                }
        }
}

/* 
 * Reads the header for an LZX-compressed block.
 *
 * @istream:            The input bitstream.
 * @block_size_ret:     A pointer to an int into which the size of the block,
 *                              in bytes, will be returned.
 * @block_type_ret:     A pointer to an int into which the type of the block
 *                              (LZX_BLOCKTYPE_*) will be returned.
 * @tables:             A pointer to a lzx_tables structure in which the 
 *                              main tree, the length tree, and possibly the
 *                              aligned offset tree will be constructed.
 * @queue:      A pointer to the least-recently-used queue into which
 *                      R0, R1, and R2 will be written (only for uncompressed
 *                      blocks, which contain this information in the header)
 */
static int lzx_read_block_header(struct input_bitstream *istream, 
                                 int *block_size_ret, int *block_type_ret, 
                                 struct lzx_tables *tables, 
                                 struct lru_queue *queue)
{
        int ret;
        int block_type;
        uint block_size;
        int s;
        int i;
        uint len;
        int32_t R[3];

        ret = bitstream_ensure_bits(istream, 4);
        if (ret != 0) {
                ERROR("Input stream overrun!\n");
                return ret;
        }

        /* The first three bits tell us what kind of block it is, and are one
         * of the LZX_BLOCKTYPE_* values.  */
        block_type = bitstream_read_bits_nocheck(istream, 3);

        /* The next bit indicates whether the block size is the default (32768),
         * indicated by a 1 bit, or whether the block size is given by the next
         * 16 bits, indicated by a 0 bit. */
        s = bitstream_read_bits_nocheck(istream, 1);

        if (s == 1) {
                block_size = 1 << 15;
        } else {
                ret = bitstream_read_bits(istream, 16, &block_size);
                if (ret != 0)
                        return ret;
                block_size = to_le16(block_size);
        }

        switch (block_type) {
        case LZX_BLOCKTYPE_ALIGNED:

                /* Read the path lengths for the elements of the aligned tree,
                 * then build it. */

                for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++) {
                        ret = bitstream_read_bits(istream, 
                                                  LZX_ALIGNEDTREE_ELEMENT_SIZE, 
                                                  &len);
                        if (ret != 0)
                                return ret;
                        tables->alignedtree_lens[i] = len;
                }
                
                LZX_DEBUG("Building the aligned tree.\n");
                ret = make_huffman_decode_table(tables->alignedtree_decode_table,
                                        LZX_ALIGNEDTREE_NUM_SYMBOLS, 
                                        LZX_ALIGNEDTREE_TABLEBITS,
                                        tables->alignedtree_lens, 8);
                if (ret != 0) {
                        ERROR("Failed to make the decode table for "
                                        "the aligned offset tree!\n");
                        return ret;
                }

                /* Fall though, since the rest of the header for aligned offset
                 * blocks is the same as that for verbatim blocks */

        case LZX_BLOCKTYPE_VERBATIM:
                if (block_type == LZX_BLOCKTYPE_VERBATIM)
                        LZX_DEBUG("Found verbatim block\n");

                LZX_DEBUG("Reading path lengths for main tree.\n");
                /* Read the path lengths for the first 256 elements of the main
                 * tree. */
                ret = lzx_read_code_lens(istream, tables->maintree_lens, 
                                         LZX_NUM_CHARS);
                if (ret != 0) {
                        ERROR("Failed to read the code lengths for "
                                        "the first 256 elements of the main "
                                        "tree!\n");
                        return ret;
                }

                /* Read the path lengths for the remaining elements of the main
                 * tree. */
                LZX_DEBUG("Reading path lengths for remaining elements of "
                                "main tree (%d elements).\n",
                                LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
                ret = lzx_read_code_lens(istream, 
                                         tables->maintree_lens + LZX_NUM_CHARS, 
                                         LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
                if (ret != 0) {
                        ERROR("Failed to read the path lengths for "
                                        "the remaining elements of the main "
                                        "tree!\n");
                        return ret;
                }

                LZX_DEBUG("Building the Huffman decoding table for the main tree.\n");

                ret = make_huffman_decode_table(tables->maintree_decode_table,
                                                LZX_MAINTREE_NUM_SYMBOLS,
                                                LZX_MAINTREE_TABLEBITS,
                                                tables->maintree_lens, 
                                                LZX_MAX_CODEWORD_LEN);
                if (ret != 0) {
                        ERROR("Failed to make the decode table for "
                                        "the main tree!\n");
                        return ret;
                }

                LZX_DEBUG("Reading path lengths for the length tree.\n");
                ret = lzx_read_code_lens(istream, tables->lentree_lens, 
                                         LZX_LENTREE_NUM_SYMBOLS);
                if (ret != 0) {
                        ERROR("Failed to read the path lengths "
                                        "for the length tree!\n");
                        return ret;
                }

                LZX_DEBUG("Building the length tree.\n");
                ret = make_huffman_decode_table(tables->lentree_decode_table,
                                                LZX_LENTREE_NUM_SYMBOLS, 
                                                LZX_LENTREE_TABLEBITS,
                                                tables->lentree_lens, 
                                                LZX_MAX_CODEWORD_LEN);
                if (ret != 0) {
                        ERROR("Failed to build the length Huffman "
                                        "tree!\n");
                        return ret;
                }

                break;

        case LZX_BLOCKTYPE_UNCOMPRESSED:
                LZX_DEBUG("Found uncompressed block\n");
                ret = align_input_bitstream(istream, true);
                if (ret != 0)
                        return ret;
                ret = bitstream_read_bytes(istream, sizeof(R), R);
                if (ret != 0)
                        return ret;
                array_to_le32(R, ARRAY_LEN(3));
                queue->R0 = R[0];
                queue->R1 = R[1];
                queue->R2 = R[2];
                break;
        default:
                LZX_DEBUG("Found invalid block\n");
                return 1;
        }
        *block_type_ret = block_type;
        *block_size_ret = block_size;
        return 0;
}

/* 
 * Decodes a compressed literal match value.  It refers to some match_offset to
 * a point earlier in the window, and some match_len, for which the data is to
 * be copied to the current position in the window.
 *
 * @main_element:       The start of the match data, as decoded using the main
 *                              tree.
 * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or
 *                      LZX_BLOCKTYPE_VERBATIM)
 * @bytes_remaining:    The amount of uncompressed data remaining to be
 *                              uncompressed.  It is an error if the match
 *                              is longer than @bytes_remaining.
 * @window:     A pointer to the window into which the uncompressed
 *                      data is being written.
 * @window_pos: The current position in the window.
 * @tables:     Contains the Huffman tables for the block (main,
 *                      length, and also aligned offset only for
 *                      LZX_BLOCKTYPE_ALIGNED)
 * @queue:      The least-recently used queue for match offsets.
 * @istream:    The input bitstream.
 *
 * Returns the length of the match, or -1 on error (match would exceed
 * the amount of data needing to be uncompressed, or match refers to data before
 * the window, or the input bitstream ended unexpectedly).
 */
static int lzx_decode_match(int main_element, int block_type, 
                            int bytes_remaining, u8 *window, int window_pos, 
                            const struct lzx_tables *tables, 
                            struct lru_queue *queue, 
                            struct input_bitstream *istream)
{
        uint length_header;
        uint position_slot;
        uint match_len;
        uint match_offset;
        uint additional_len;
        uint num_extra_bits;
        uint verbatim_bits;
        uint aligned_bits;
        int ret;
        int i;
        u8 *match_dest;
        u8 *match_src;

        /* The main element is offset by 256 because values under 256 indicate a
         * literal value. */
        main_element -= LZX_NUM_CHARS;

        /* The length header consists of the lower 3 bits of the main element.
         * The position slot is the rest of it. */
        length_header = main_element & LZX_NUM_PRIMARY_LENS;
        position_slot = main_element >> 3;

        /* If the length_header is less than LZX_NUM_PRIMARY_LENS (= 7), it
         * gives the match length as the offset from LZX_MIN_MATCH.  Otherwise,
         * the length is given by an additional symbol encoded using the length
         * tree, offset by 9 (LZX_MIN_MATCH + LZX_NUM_PRIMARY_LENS) */
        match_len = LZX_MIN_MATCH + length_header;
        if (length_header == LZX_NUM_PRIMARY_LENS) {
                ret = read_huffsym_using_lentree(istream, tables, 
                                                &additional_len);
                if (ret != 0)
                        return -1;
                match_len += additional_len;
        }


        /* If the position_slot is 0, 1, or 2, the match offset is retrieved
         * from the LRU queue.  Otherwise, the match offset is not in the LRU
         * queue. */
        switch (position_slot) {
        case 0:
                match_offset = queue->R0;
                break;
        case 1:
                match_offset = queue->R1;
                swap(queue->R0, queue->R1);
                break;
        case 2:
                /* The queue doesn't work quite the same as a real LRU queue,
                 * since using the R2 offset doesn't bump the R1 offset down to
                 * R2. */
                match_offset = queue->R2;
                swap(queue->R0, queue->R2);
                break;
        default:
                /* Otherwise, the offset was not encoded as one the offsets in
                 * the queue.  Depending on the position slot, there is a
                 * certain number of extra bits that need to be read to fully
                 * decode the match offset. */

                /* Look up the number of extra bits that need to be read. */
                num_extra_bits = lzx_extra_bits[position_slot];

                /* For aligned blocks, if there are at least 3 extra bits, the
                 * actual number of extra bits is 3 less, and they encode a
                 * number of 8-byte words that are added to the offset; there
                 * is then an additional symbol read using the aligned tree that
                 * specifies the actual byte alignment. */
                if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {

                        /* There is an error in the LZX "specification" at this
                         * point; it indicates that a Huffman symbol is to be
                         * read only if num_extra_bits is greater than 3, but
                         * actually it is if num_extra_bits is greater than or
                         * equal to 3.  (Note that in the case with
                         * num_extra_bits == 3, the assignment to verbatim_bits
                         * will just set it to 0. ) */
                        ret = bitstream_read_bits(istream, num_extra_bits - 3, 
                                                                &verbatim_bits);
                        if (ret != 0)
                                return -1;

                        verbatim_bits <<= 3;

                        ret = read_huffsym_using_alignedtree(istream, tables, 
                                                             &aligned_bits);
                        if (ret != 0)
                                return -1;
                } else {
                        /* For non-aligned blocks, or for aligned blocks with
                         * less than 3 extra bits, the extra bits are added
                         * directly to the match offset, and the correction for
                         * the alignment is taken to be 0. */
                        ret = bitstream_read_bits(istream, num_extra_bits, 
                                                  &verbatim_bits);
                        if (ret != 0)
                                return -1;

                        aligned_bits = 0;
                }

                /* Calculate the match offset. */
                match_offset = lzx_position_base[position_slot] + verbatim_bits + 
                                                        aligned_bits - 2;

                /* Update the LRU queue. */
                queue->R2 = queue->R1;
                queue->R1 = queue->R0;
                queue->R0 = match_offset;
                break;
        }

        /* Verify that the match is in the bounds of the part of the window
         * currently in use, then copy the source of the match to the current
         * position. */
        match_dest = window + window_pos;
        match_src = match_dest - match_offset;

        if (match_len > bytes_remaining) {
                ERROR("Match of length %d bytes overflows uncompressed "
                                "block size!\n", match_len);
                return -1;
        }

        if (match_src < window) {
                ERROR("Match of length %d bytes references data "
                                "before window (match_offset = %d, "
                                "window_pos = %d)\n", match_len,
                                match_offset, window_pos);
                return -1;
        }

        for (i = 0; i < match_len; i++)
                match_dest[i] = match_src[i];

        return match_len;
}



/* Undo the 'E8' preprocessing, where the targets of x86 CALL instructions were
 * changed from relative offsets to absolute offsets.  This type of
 * preprocessing can be used on any binary data even if it is not actually
 * machine code.  It seems to always be used in WIM files, even though there is
 * no bit to indicate that it actually is used, unlike in the LZX compressed
 * format as used in other file formats, where a bit is reserved for that
 * purpose. */
static void undo_call_insn_preprocessing(u8 uncompressed_data[], 
                                         uint uncompressed_data_len)
{
        int i = 0;
        int file_size = LZX_MAGIC_FILESIZE;
        int32_t abs_offset;
        int32_t rel_offset;

        /* Not enabled in the last 6 bytes, which means the 5-byte call
         * instruction cannot start in the last *10* bytes. */
        while (i < uncompressed_data_len - 10) { 
                if (uncompressed_data[i] != 0xe8) {
                        i++;
                        continue;
                }
                abs_offset = to_le32(*(int32_t*)(uncompressed_data + i + 1));

                if (abs_offset >= -i && abs_offset < file_size) {
                        if (abs_offset >= 0) {
                                /* "good translation" */
                                rel_offset = abs_offset - i;
                        } else {
                                /* "compensating translation" */
                                rel_offset = abs_offset + file_size;
                        }
                        *(int32_t*)(uncompressed_data + i + 1) = 
                                                to_le32(rel_offset);
                }
                i += 5;
        }
}

/* 
 * Decompresses a compressed block of data from which the header has already
 * been read.
 *
 * @block_type: The type of the block (LZX_BLOCKTYPE_VERBATIM or
 *              LZX_BLOCKTYPE_ALIGNED)
 * @block_size: The size of the block, in bytes.
 * @window:     Pointer to the decompression window.
 * @window_pos: The current position in the window.  Will be 0 for the first
 *                      block.  
 * @tables:     The Huffman decoding tables for the block (main, length, and
 *                      aligned offset, the latter only for LZX_BLOCKTYPE_ALIGNED)
 * @queue:      The least-recently-used queue for match offsets.
 * @istream:    The input bitstream for the compressed literals.
 */
static int lzx_decompress_block(int block_type, int block_size, u8 *window, 
                                int window_pos, 
                                const struct lzx_tables *tables, 
                                struct lru_queue *queue, 
                                struct input_bitstream *istream)
{
        uint bytes_remaining;
        uint main_element;
        int match_len;
        int ret;

        bytes_remaining = block_size;
        while (bytes_remaining > 0) {

                ret = read_huffsym_using_maintree(istream, tables, 
                                                  &main_element);
                if (ret != 0)
                        return ret;

                if (main_element < LZX_NUM_CHARS) {
                        /* literal: 0 to LZX_NUM_CHARS - 1 */
                        window[window_pos + block_size - bytes_remaining] = 
                                                        main_element;
                        bytes_remaining--;
                } else {
                        /* match: LZX_NUM_CHARS to LZX_MAINTREE_NUM_SYMBOLS - 1 */
                        match_len = lzx_decode_match(main_element, 
                                                block_type, bytes_remaining, window,
                                                block_size + window_pos - 
                                                        bytes_remaining,
                                                tables, queue, istream);
                        if (match_len == -1)
                                return 1;

                        bytes_remaining -= match_len;
                }
        }
        return 0;
}

/* 
 * Decompresses a block of LZX-compressed data using a window size of 32768.
 *
 * @compressed_data:    A pointer to the compressed data.
 * @compressed_len:     The length of the compressed data, in bytes.  
 * @uncompressed_data:  A pointer to the buffer into which to write the
 *                              uncompressed data.
 * @uncompressed_len:   The length of the uncompressed data.
 *
 * Return non-zero on failure.
 */
int lzx_decompress(const void *compressed_data, uint compressed_len, 
                   void *uncompressed_data, uint uncompressed_len)
{
        struct lzx_tables       tables;
        struct input_bitstream  istream;
        struct lru_queue        queue;
        uint                    bytes_remaining;
        int ret;
        int block_size;
        int block_type;

        LZX_DEBUG("lzx_decompress (compressed_data = %p, compressed_len = %d, "
                        "uncompressed_data = %p, uncompressed_len = %d)\n",
                        compressed_data, compressed_len, uncompressed_data,
                        uncompressed_len);

        wimlib_assert(uncompressed_len <= 32768);

        memset(tables.maintree_lens, 0, sizeof(tables.maintree_lens));
        memset(tables.lentree_lens, 0, sizeof(tables.lentree_lens));
        queue.R0 = 1;
        queue.R1 = 1;
        queue.R2 = 1;
        bytes_remaining = uncompressed_len;

        init_input_bitstream(&istream, compressed_data, compressed_len);

        /* The compressed data will consist of one or more blocks.  The
         * following loop decompresses one block, and it runs until there all
         * the compressed data has been decompressed, so there are no more
         * blocks.  */

        while (bytes_remaining != 0) {

                LZX_DEBUG("Reading block header.\n");
                ret = lzx_read_block_header(&istream, &block_size, &block_type, 
                                                        &tables, &queue);
                if (ret != 0)
                        return ret;

                LZX_DEBUG("block_size = %d, bytes_remaining = %d\n",
                                block_size, bytes_remaining);

                if (block_size > bytes_remaining) {
                        ERROR("Expected a block size of at most %d "
                                        "bytes (found %d bytes)!\n", 
                                        bytes_remaining, block_size);
                        return 1;
                }

                if (block_type == LZX_BLOCKTYPE_VERBATIM || 
                                        block_type == LZX_BLOCKTYPE_ALIGNED) {
                        if (block_type == LZX_BLOCKTYPE_VERBATIM)
                                LZX_DEBUG("LZX_BLOCKTYPE_VERBATIM\n");
                        else
                                LZX_DEBUG("LZX_BLOCKTYPE_ALIGNED\n");

                        ret = lzx_decompress_block(block_type, 
                                           block_size, uncompressed_data,
                                           uncompressed_len - bytes_remaining, 
                                           &tables, &queue, &istream);
                        if (ret != 0)
                                return ret;
                } else if (block_type == LZX_BLOCKTYPE_UNCOMPRESSED) {
                        LZX_DEBUG("LZX_BLOCKTYPE_UNCOMPRESSED\n");
                        ret = bitstream_read_bytes(&istream, block_size, 
                                                   uncompressed_data + 
                                                   uncompressed_len - 
                                                   bytes_remaining);
                        if (ret != 0)
                                return ret;
                        if (block_size & 1)
                                align_input_bitstream(&istream, false);
                } else {
                        ERROR("Unrecognized block type!\n");
                        return 1;
                }

                bytes_remaining -= block_size;

                if (bytes_remaining != 0)
                        LZX_DEBUG("%d bytes remaining\n", bytes_remaining);

        }

        if (uncompressed_len >= 10)
                undo_call_insn_preprocessing(uncompressed_data, uncompressed_len);

        return 0;
}