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   1 /*
   2  * lzx-decompress.c
   3  *
   4  * LZX decompression routines, originally based on code taken from cabextract
   5  * v0.5, which was, itself, a modified version of the lzx decompression code
   6  * from unlzx.
   7  */
   8
   9 /*
  10  * Copyright (C) 2012, 2013, 2014 Eric Biggers
  11  *
  12  * This file is part of wimlib, a library for working with WIM files.
  13  *
  14  * wimlib is free software; you can redistribute it and/or modify it under the
  15  * terms of the GNU General Public License as published by the Free
  16  * Software Foundation; either version 3 of the License, or (at your option)
  17  * any later version.
  18  *
  19  * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
  20  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  21  * A PARTICULAR PURPOSE. See the GNU General Public License for more
  22  * details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with wimlib; if not, see http://www.gnu.org/licenses/.
  26  */
  27
  28 /*
  29  * LZX is an LZ77 and Huffman-code based compression format that has many
  30  * similarities to the DEFLATE format used in zlib.  The compression ratio is as
  31  * good or better than DEFLATE.
  32  *
  33  * Some notes on the LZX compression format as used in Windows Imaging (WIM)
  34  * files:
  35  *
  36  * A compressed WIM resource consists of a table of chunk offsets followed by
  37  * the compressed chunks themselves.  All compressed chunks except possibly the
  38  * last decompress to a fixed number of bytes, by default 32768.  This is quite
  39  * similar to the cabinet (.cab) file format, but they are not the same.
  40  * According to the cabinet format documentation, the LZX block size is
  41  * independent from the CFDATA blocks, and an LZX block may span several CFDATA
  42  * blocks.  However, in WIMs, LZX blocks do not appear to ever span multiple WIM
  43  * chunks.  Note that this means any WIM chunk may be decompressed or compressed
  44  * independently from any other chunk, which allows random access.
  45  *
  46  * An LZX compressed WIM chunk contains one or more LZX blocks of the aligned,
  47  * verbatim, or uncompressed block types.  For aligned and verbatim blocks, the
  48  * size of the block in uncompressed bytes is specified by a bit following the 3
  49  * bits that specify the block type, possibly followed by an additional 16 bits.
  50  * '1' means to use the default block size (equal to 32768, the default size of
  51  * a WIM chunk), while '0' means that the block size is provided by the next 16
  52  * bits.
  53  *
  54  * The cabinet format, as documented, allows for the possibility that a
  55  * compressed CFDATA chunk is up to 6144 bytes larger than the data it
  56  * uncompresses to.  However, in the WIM format it appears that every chunk that
  57  * would be 32768 bytes or more when compressed is actually stored fully
  58  * uncompressed.
  59  *
  60  * The 'e8' preprocessing step that changes x86 call instructions to use
  61  * absolute offsets instead of relative offsets relies on a filesize parameter.
  62  * There is no such parameter for this in the WIM files (even though the size of
  63  * the file resource could be used for this purpose), and instead a magic file
  64  * size of 12000000 is used.  The 'e8' preprocessing is always done, and there
  65  * is no bit to indicate whether it is done or not.
  66  */
  67
  68 /*
  69  * Some more notes about errors in Microsoft's LZX documentation:
  70  *
  71  * Microsoft's LZX document and their implementation of the com.ms.util.cab Java
  72  * package do not concur.
  73  *
  74  * In the LZX document, there is a table showing the correlation between window
  75  * size and the number of position slots. It states that the 1MB window = 40
  76  * slots and the 2MB window = 42 slots. In the implementation, 1MB = 42 slots,
  77  * 2MB = 50 slots. The actual calculation is 'find the first slot whose position
  78  * base is equal to or more than the required window size'. This would explain
  79  * why other tables in the document refer to 50 slots rather than 42.
  80  *
  81  * The constant NUM_PRIMARY_LENS used in the decompression pseudocode is not
  82  * defined in the specification.
  83  *
  84  * The LZX document states that aligned offset blocks have their aligned offset
  85  * Huffman tree AFTER the main and length trees. The implementation suggests
  86  * that the aligned offset tree is BEFORE the main and length trees.
  87  *
  88  * The LZX document decoding algorithm states that, in an aligned offset block,
  89  * if an extra_bits value is 1, 2 or 3, then that number of bits should be read
  90  * and the result added to the match offset. This is correct for 1 and 2, but
  91  * not 3, where just a Huffman symbol (using the aligned tree) should be read.
  92  *
  93  * Regarding the E8 preprocessing, the LZX document states 'No translation may
  94  * be performed on the last 6 bytes of the input block'. This is correct.
  95  * However, the pseudocode provided checks for the *E8 leader* up to the last 6
  96  * bytes. If the leader appears between -10 and -7 bytes from the end, this
  97  * would cause the next four bytes to be modified, at least one of which would
  98  * be in the last 6 bytes, which is not allowed according to the spec.
  99  *
 100  * The specification states that the Huffman trees must always contain at least
 101  * one element. However, many CAB files contain blocks where the length tree is
 102  * completely empty (because there are no matches), and this is expected to
 103  * succeed.
 104  */
 105
 106 #ifdef HAVE_CONFIG_H
 107 #  include "config.h"
 108 #endif
 109
 110 #include "wimlib.h"
 111 #include "wimlib/decompressor_ops.h"
 112 #include "wimlib/decompress_common.h"
 113 #include "wimlib/lzx.h"
 114 #include "wimlib/util.h"
 115
 116 #include <string.h>
 117
 118 /* Huffman decoding tables and maps from symbols to code lengths. */
 119 struct lzx_tables {
 120
 121         u16 maintree_decode_table[(1 << LZX_MAINCODE_TABLEBITS) +
 122                                         (LZX_MAINCODE_MAX_NUM_SYMBOLS * 2)]
 123                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 124         u8 maintree_lens[LZX_MAINCODE_MAX_NUM_SYMBOLS];
 125
 126
 127         u16 lentree_decode_table[(1 << LZX_LENCODE_TABLEBITS) +
 128                                         (LZX_LENCODE_NUM_SYMBOLS * 2)]
 129                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 130         u8 lentree_lens[LZX_LENCODE_NUM_SYMBOLS];
 131
 132
 133         u16 alignedtree_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) +
 134                                         (LZX_ALIGNEDCODE_NUM_SYMBOLS * 2)]
 135                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 136         u8 alignedtree_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS];
 137 } _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 138
 139 struct lzx_decompressor {
 140         u32 max_window_size;
 141         unsigned num_main_syms;
 142         struct lzx_tables tables;
 143 };
 144
 145 /*
 146  * Reads a Huffman-encoded symbol using the pre-tree.
 147  */
 148 static inline u16
 149 read_huffsym_using_pretree(struct input_bitstream *istream,
 150                            const u16 pretree_decode_table[])
 151 {
 152         return read_huffsym(istream, pretree_decode_table,
 153                             LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN);
 154 }
 155
 156 /* Reads a Huffman-encoded symbol using the main tree. */
 157 static inline u16
 158 read_huffsym_using_maintree(struct input_bitstream *istream,
 159                             const struct lzx_tables *tables)
 160 {
 161         return read_huffsym(istream, tables->maintree_decode_table,
 162                             LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN);
 163 }
 164
 165 /* Reads a Huffman-encoded symbol using the length tree. */
 166 static inline u16
 167 read_huffsym_using_lentree(struct input_bitstream *istream,
 168                            const struct lzx_tables *tables)
 169 {
 170         return read_huffsym(istream, tables->lentree_decode_table,
 171                             LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN);
 172 }
 173
 174 /* Reads a Huffman-encoded symbol using the aligned offset tree. */
 175 static inline u16
 176 read_huffsym_using_alignedtree(struct input_bitstream *istream,
 177                                const struct lzx_tables *tables)
 178 {
 179         return read_huffsym(istream, tables->alignedtree_decode_table,
 180                             LZX_ALIGNEDCODE_TABLEBITS, LZX_MAX_ALIGNED_CODEWORD_LEN);
 181 }
 182
 183 /*
 184  * Reads the pretree from the input, then uses the pretree to decode @num_lens
 185  * code length values from the input.
 186  *
 187  * @istream:    The bit stream for the input.  It is positioned on the beginning
 188  *                      of the pretree for the code length values.
 189  * @lens:       An array that contains the length values from the previous time
 190  *                      the code lengths for this Huffman tree were read, or all
 191  *                      0's if this is the first time.
 192  * @num_lens:   Number of length values to decode and return.
 193  *
 194  */
 195 static int
 196 lzx_read_code_lens(struct input_bitstream *istream, u8 lens[],
 197                    unsigned num_lens)
 198 {
 199         /* Declare the decoding table and length table for the pretree. */
 200         u16 pretree_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
 201                                         (LZX_PRECODE_NUM_SYMBOLS * 2)]
 202                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 203         u8 pretree_lens[LZX_PRECODE_NUM_SYMBOLS];
 204         unsigned i;
 205         int ret;
 206
 207         /* Read the code lengths of the pretree codes.  There are 20 lengths of
 208          * 4 bits each. */
 209         for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
 210                 pretree_lens[i] = bitstream_read_bits(istream,
 211                                                       LZX_PRECODE_ELEMENT_SIZE);
 212         }
 213
 214         /* Make the decoding table for the pretree. */
 215         ret = make_huffman_decode_table(pretree_decode_table,
 216                                         LZX_PRECODE_NUM_SYMBOLS,
 217                                         LZX_PRECODE_TABLEBITS,
 218                                         pretree_lens,
 219                                         LZX_MAX_PRE_CODEWORD_LEN);
 220         if (ret)
 221                 return ret;
 222
 223         /* Pointer past the last length value that needs to be filled in. */
 224         u8 *lens_end = lens + num_lens;
 225
 226         while (1) {
 227
 228                 /* Decode a symbol from the input.  If the symbol is between 0
 229                  * and 16, it is the difference from the old length.  If it is
 230                  * between 17 and 19, it is a special code that indicates that
 231                  * some number of the next lengths are all 0, or some number of
 232                  * the next lengths are all equal to the next symbol in the
 233                  * input. */
 234                 unsigned tree_code;
 235                 u32 num_zeroes;
 236                 unsigned code;
 237                 u32 num_same;
 238                 signed char value;
 239
 240                 tree_code = read_huffsym_using_pretree(istream,
 241                                                        pretree_decode_table);
 242                 switch (tree_code) {
 243                 case 17: /* Run of 0's */
 244                         num_zeroes = bitstream_read_bits(istream, 4);
 245                         num_zeroes += 4;
 246                         while (num_zeroes--) {
 247                                 *lens = 0;
 248                                 if (++lens == lens_end)
 249                                         return 0;
 250                         }
 251                         break;
 252                 case 18: /* Longer run of 0's */
 253                         num_zeroes = bitstream_read_bits(istream, 5);
 254                         num_zeroes += 20;
 255                         while (num_zeroes--) {
 256                                 *lens = 0;
 257                                 if (++lens == lens_end)
 258                                         return 0;
 259                         }
 260                         break;
 261                 case 19: /* Run of identical lengths */
 262                         num_same = bitstream_read_bits(istream, 1);
 263                         num_same += 4;
 264                         code = read_huffsym_using_pretree(istream,
 265                                                           pretree_decode_table);
 266                         value = (signed char)*lens - (signed char)code;
 267                         if (value < 0)
 268                                 value += 17;
 269                         while (num_same--) {
 270                                 *lens = value;
 271                                 if (++lens == lens_end)
 272                                         return 0;
 273                         }
 274                         break;
 275                 default: /* Difference from old length. */
 276                         value = (signed char)*lens - (signed char)tree_code;
 277                         if (value < 0)
 278                                 value += 17;
 279                         *lens = value;
 280                         if (++lens == lens_end)
 281                                 return 0;
 282                         break;
 283                 }
 284         }
 285 }
 286
 287 /*
 288  * Reads the header for an LZX-compressed block.
 289  *
 290  * @istream:            The input bitstream.
 291  * @block_size_ret:     A pointer to an int into which the size of the block,
 292  *                              in bytes, will be returned.
 293  * @block_type_ret:     A pointer to an int into which the type of the block
 294  *                              (LZX_BLOCKTYPE_*) will be returned.
 295  * @tables:             A pointer to an lzx_tables structure in which the
 296  *                              main tree, the length tree, and possibly the
 297  *                              aligned offset tree will be constructed.
 298  * @queue:      A pointer to the least-recently-used queue into which
 299  *                      R0, R1, and R2 will be written (only for uncompressed
 300  *                      blocks, which contain this information in the header)
 301  */
 302 static int
 303 lzx_read_block_header(struct input_bitstream *istream,
 304                       unsigned num_main_syms,
 305                       unsigned max_window_size,
 306                       unsigned *block_size_ret,
 307                       unsigned *block_type_ret,
 308                       struct lzx_tables *tables,
 309                       struct lzx_lru_queue *queue)
 310 {
 311         int ret;
 312         unsigned block_type;
 313         unsigned block_size;
 314
 315         bitstream_ensure_bits(istream, 4);
 316
 317         /* The first three bits tell us what kind of block it is, and are one
 318          * of the LZX_BLOCKTYPE_* values.  */
 319         block_type = bitstream_pop_bits(istream, 3);
 320
 321         /* Read the block size.  This mirrors the behavior
 322          * lzx_write_compressed_block() in lzx-compress.c; see that for more
 323          * details.  */
 324         if (bitstream_pop_bits(istream, 1)) {
 325                 block_size = LZX_DEFAULT_BLOCK_SIZE;
 326         } else {
 327                 u32 tmp;
 328                 block_size = 0;
 329
 330                 tmp = bitstream_read_bits(istream, 8);
 331                 block_size |= tmp;
 332                 tmp = bitstream_read_bits(istream, 8);
 333                 block_size <<= 8;
 334                 block_size |= tmp;
 335
 336                 if (max_window_size >= 65536) {
 337                         tmp = bitstream_read_bits(istream, 8);
 338                         block_size <<= 8;
 339                         block_size |= tmp;
 340                 }
 341         }
 342
 343         switch (block_type) {
 344         case LZX_BLOCKTYPE_ALIGNED:
 345                 /* Read the path lengths for the elements of the aligned tree,
 346                  * then build it. */
 347
 348                 for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
 349                         tables->alignedtree_lens[i] =
 350                                 bitstream_read_bits(istream,
 351                                                     LZX_ALIGNEDCODE_ELEMENT_SIZE);
 352                 }
 353
 354                 LZX_DEBUG("Building the aligned tree.");
 355                 ret = make_huffman_decode_table(tables->alignedtree_decode_table,
 356                                                 LZX_ALIGNEDCODE_NUM_SYMBOLS,
 357                                                 LZX_ALIGNEDCODE_TABLEBITS,
 358                                                 tables->alignedtree_lens,
 359                                                 LZX_MAX_ALIGNED_CODEWORD_LEN);
 360                 if (ret) {
 361                         LZX_DEBUG("Failed to make the decode table for the "
 362                                   "aligned offset tree");
 363                         return ret;
 364                 }
 365
 366                 /* Fall though, since the rest of the header for aligned offset
 367                  * blocks is the same as that for verbatim blocks */
 368
 369         case LZX_BLOCKTYPE_VERBATIM:
 370                 if (block_type == LZX_BLOCKTYPE_VERBATIM)
 371                         LZX_DEBUG("Found verbatim block.");
 372
 373                 LZX_DEBUG("Reading path lengths for main tree.");
 374                 /* Read the path lengths for the first 256 elements of the main
 375                  * tree. */
 376                 ret = lzx_read_code_lens(istream, tables->maintree_lens,
 377                                          LZX_NUM_CHARS);
 378                 if (ret) {
 379                         LZX_DEBUG("Failed to read the code lengths for the "
 380                                   "first 256 elements of the main tree");
 381                         return ret;
 382                 }
 383
 384                 /* Read the path lengths for the remaining elements of the main
 385                  * tree. */
 386                 LZX_DEBUG("Reading path lengths for remaining elements of "
 387                           "main tree (%d elements).",
 388                           num_main_syms - LZX_NUM_CHARS);
 389                 ret = lzx_read_code_lens(istream,
 390                                          tables->maintree_lens + LZX_NUM_CHARS,
 391                                          num_main_syms - LZX_NUM_CHARS);
 392                 if (ret) {
 393                         LZX_DEBUG("Failed to read the path lengths for the "
 394                                   "remaining elements of the main tree");
 395                         return ret;
 396                 }
 397
 398                 LZX_DEBUG("Building the Huffman decoding "
 399                           "table for the main tree.");
 400
 401                 ret = make_huffman_decode_table(tables->maintree_decode_table,
 402                                                 num_main_syms,
 403                                                 LZX_MAINCODE_TABLEBITS,
 404                                                 tables->maintree_lens,
 405                                                 LZX_MAX_MAIN_CODEWORD_LEN);
 406                 if (ret) {
 407                         LZX_DEBUG("Failed to make the decode "
 408                                   "table for the main tree");
 409                         return ret;
 410                 }
 411
 412                 LZX_DEBUG("Reading path lengths for the length tree.");
 413                 ret = lzx_read_code_lens(istream, tables->lentree_lens,
 414                                          LZX_LENCODE_NUM_SYMBOLS);
 415                 if (ret) {
 416                         LZX_DEBUG("Failed to read the path "
 417                                   "lengths for the length tree");
 418                         return ret;
 419                 }
 420
 421                 LZX_DEBUG("Building the length tree.");
 422                 ret = make_huffman_decode_table(tables->lentree_decode_table,
 423                                                 LZX_LENCODE_NUM_SYMBOLS,
 424                                                 LZX_LENCODE_TABLEBITS,
 425                                                 tables->lentree_lens,
 426                                                 LZX_MAX_LEN_CODEWORD_LEN);
 427                 if (ret) {
 428                         LZX_DEBUG("Failed to build the length Huffman tree");
 429                         return ret;
 430                 }
 431                 /* The bitstream of compressed literals and matches for this
 432                  * block directly follows and will be read in
 433                  * lzx_decompress_block(). */
 434                 break;
 435         case LZX_BLOCKTYPE_UNCOMPRESSED:
 436                 LZX_DEBUG("Found uncompressed block.");
 437                 /* Before reading the three LRU match offsets from the
 438                  * uncompressed block header, the stream needs to be aligned on
 439                  * a 16-bit boundary.  But, unexpectedly, if the stream is
 440                  * *already* aligned, the correct thing to do is to throw away
 441                  * the next 16 bits. */
 442                 if (istream->bitsleft == 0) {
 443                         if (istream->data_bytes_left < 14) {
 444                                 LZX_DEBUG("Insufficient length in "
 445                                           "uncompressed block");
 446                                 return -1;
 447                         }
 448                         istream->data += 2;
 449                         istream->data_bytes_left -= 2;
 450                 } else {
 451                         if (istream->data_bytes_left < 12) {
 452                                 LZX_DEBUG("Insufficient length in "
 453                                           "uncompressed block");
 454                                 return -1;
 455                         }
 456                         istream->bitsleft = 0;
 457                         istream->bitbuf = 0;
 458                 }
 459                 queue->R[0] = le32_to_cpu(*(le32*)(istream->data + 0));
 460                 queue->R[1] = le32_to_cpu(*(le32*)(istream->data + 4));
 461                 queue->R[2] = le32_to_cpu(*(le32*)(istream->data + 8));
 462                 istream->data += 12;
 463                 istream->data_bytes_left -= 12;
 464                 /* The uncompressed data of this block directly follows and will
 465                  * be read in lzx_decompress(). */
 466                 break;
 467         default:
 468                 LZX_DEBUG("Found invalid block");
 469                 return -1;
 470         }
 471         *block_type_ret = block_type;
 472         *block_size_ret = block_size;
 473         return 0;
 474 }
 475
 476 /*
 477  * Decodes a compressed match from a block of LZX-compressed data.  A match
 478  * refers to some match_offset to a point earlier in the window as well as some
 479  * match_len, for which the data is to be copied to the current position in the
 480  * window.
 481  *
 482  * @main_element:       The start of the match data, as decoded using the main
 483  *                      tree.
 484  *
 485  * @block_type:         The type of the block (LZX_BLOCKTYPE_ALIGNED or
 486  *                      LZX_BLOCKTYPE_VERBATIM)
 487  *
 488  * @bytes_remaining:    The amount of uncompressed data remaining to be
 489  *                      uncompressed in this block.  It is an error if the match
 490  *                      is longer than this number.
 491  *
 492  * @window:             A pointer to the window into which the uncompressed
 493  *                      data is being written.
 494  *
 495  * @window_pos:         The current byte offset in the window.
 496  *
 497  * @tables:             The Huffman decoding tables for this LZX block (main
 498  *                      code, length code, and for LZX_BLOCKTYPE_ALIGNED blocks,
 499  *                      also the aligned offset code).
 500  *
 501  * @queue:              The least-recently used queue for match offsets.
 502  *
 503  * @istream:            The input bitstream.
 504  *
 505  * Returns the length of the match, or a negative number on error.  The possible
 506  * error cases are:
 507  *      - Match would exceed the amount of data remaining to be uncompressed.
 508  *      - Match refers to data before the window.
 509  *      - The input bitstream ended unexpectedly.
 510  */
 511 static int
 512 lzx_decode_match(unsigned main_element, int block_type,
 513                  unsigned bytes_remaining, u8 *window,
 514                  unsigned window_pos,
 515                  const struct lzx_tables *tables,
 516                  struct lzx_lru_queue *queue,
 517                  struct input_bitstream *istream)
 518 {
 519         unsigned length_header;
 520         unsigned position_slot;
 521         unsigned match_len;
 522         unsigned match_offset;
 523         unsigned num_extra_bits;
 524         u32 verbatim_bits;
 525         u32 aligned_bits;
 526         unsigned i;
 527         u8 *match_dest;
 528         u8 *match_src;
 529
 530         /* The main element is offset by 256 because values under 256 indicate a
 531          * literal value. */
 532         main_element -= LZX_NUM_CHARS;
 533
 534         /* The length header consists of the lower 3 bits of the main element.
 535          * The position slot is the rest of it. */
 536         length_header = main_element & LZX_NUM_PRIMARY_LENS;
 537         position_slot = main_element >> 3;
 538
 539         /* If the length_header is less than LZX_NUM_PRIMARY_LENS (= 7), it
 540          * gives the match length as the offset from LZX_MIN_MATCH_LEN.
 541          * Otherwise, the length is given by an additional symbol encoded using
 542          * the length tree, offset by 9 (LZX_MIN_MATCH_LEN +
 543          * LZX_NUM_PRIMARY_LENS) */
 544         match_len = LZX_MIN_MATCH_LEN + length_header;
 545         if (length_header == LZX_NUM_PRIMARY_LENS)
 546                 match_len += read_huffsym_using_lentree(istream, tables);
 547
 548         /* If the position_slot is 0, 1, or 2, the match offset is retrieved
 549          * from the LRU queue.  Otherwise, the match offset is not in the LRU
 550          * queue. */
 551         if (position_slot <= 2) {
 552                 /* Note: This isn't a real LRU queue, since using the R2 offset
 553                  * doesn't bump the R1 offset down to R2.  This quirk allows all
 554                  * 3 recent offsets to be handled by the same code.  (For R0,
 555                  * the swap is a no-op.)  */
 556                 match_offset = queue->R[position_slot];
 557                 queue->R[position_slot] = queue->R[0];
 558                 queue->R[0] = match_offset;
 559         } else {
 560                 /* Otherwise, the offset was not encoded as one the offsets in
 561                  * the queue.  Depending on the position slot, there is a
 562                  * certain number of extra bits that need to be read to fully
 563                  * decode the match offset. */
 564
 565                 /* Look up the number of extra bits that need to be read. */
 566                 num_extra_bits = lzx_get_num_extra_bits(position_slot);
 567
 568                 /* For aligned blocks, if there are at least 3 extra bits, the
 569                  * actual number of extra bits is 3 less, and they encode a
 570                  * number of 8-byte words that are added to the offset; there
 571                  * is then an additional symbol read using the aligned tree that
 572                  * specifies the actual byte alignment. */
 573                 if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {
 574
 575                         /* There is an error in the LZX "specification" at this
 576                          * point; it indicates that a Huffman symbol is to be
 577                          * read only if num_extra_bits is greater than 3, but
 578                          * actually it is if num_extra_bits is greater than or
 579                          * equal to 3.  (Note that in the case with
 580                          * num_extra_bits == 3, the assignment to verbatim_bits
 581                          * will just set it to 0. ) */
 582                         verbatim_bits = bitstream_read_bits(istream,
 583                                                             num_extra_bits - 3);
 584                         verbatim_bits <<= 3;
 585                         aligned_bits = read_huffsym_using_alignedtree(istream,
 586                                                                       tables);
 587                 } else {
 588                         /* For non-aligned blocks, or for aligned blocks with
 589                          * less than 3 extra bits, the extra bits are added
 590                          * directly to the match offset, and the correction for
 591                          * the alignment is taken to be 0. */
 592                         verbatim_bits = bitstream_read_bits(istream, num_extra_bits);
 593                         aligned_bits = 0;
 594                 }
 595
 596                 /* Calculate the match offset. */
 597                 match_offset = lzx_position_base[position_slot] +
 598                                verbatim_bits + aligned_bits - LZX_OFFSET_OFFSET;
 599
 600                 /* Update the LRU queue. */
 601                 queue->R[2] = queue->R[1];
 602                 queue->R[1] = queue->R[0];
 603                 queue->R[0] = match_offset;
 604         }
 605
 606         /* Verify that the match is in the bounds of the part of the window
 607          * currently in use, then copy the source of the match to the current
 608          * position. */
 609
 610         if (unlikely(match_len > bytes_remaining)) {
 611                 LZX_DEBUG("Match of length %u bytes overflows "
 612                           "uncompressed block size", match_len);
 613                 return -1;
 614         }
 615
 616         if (unlikely(match_offset > window_pos)) {
 617                 LZX_DEBUG("Match of length %u bytes references "
 618                           "data before window (match_offset = %u, "
 619                           "window_pos = %u)",
 620                           match_len, match_offset, window_pos);
 621                 return -1;
 622         }
 623
 624         match_dest = window + window_pos;
 625         match_src = match_dest - match_offset;
 626
 627 #if 0
 628         printf("Match: src %u, dst %u, len %u\n", match_src - window,
 629                                                 match_dest - window,
 630                                                 match_len);
 631         putchar('|');
 632         for (i = 0; i < match_len; i++) {
 633                 match_dest[i] = match_src[i];
 634                 putchar(match_src[i]);
 635         }
 636         putchar('|');
 637         putchar('\n');
 638 #else
 639         for (i = 0; i < match_len; i++)
 640                 match_dest[i] = match_src[i];
 641 #endif
 642
 643         return match_len;
 644 }
 645
 646 /*
 647  * Decompresses an LZX-compressed block of data from which the header has already
 648  * been read.
 649  *
 650  * @block_type: The type of the block (LZX_BLOCKTYPE_VERBATIM or
 651  *              LZX_BLOCKTYPE_ALIGNED)
 652  * @block_size: The size of the block, in bytes.
 653  * @window:     Pointer to the decompression window.
 654  * @window_pos: The current position in the window.  Will be 0 for the first
 655  *                      block.
 656  * @tables:     The Huffman decoding tables for the block (main, length, and
 657  *                      aligned offset, the latter only for LZX_BLOCKTYPE_ALIGNED)
 658  * @queue:      The least-recently-used queue for match offsets.
 659  * @istream:    The input bitstream for the compressed literals.
 660  */
 661 static int
 662 lzx_decompress_block(int block_type, unsigned block_size,
 663                      u8 *window,
 664                      unsigned window_pos,
 665                      const struct lzx_tables *tables,
 666                      struct lzx_lru_queue *queue,
 667                      struct input_bitstream *istream)
 668 {
 669         unsigned main_element;
 670         unsigned end;
 671         int match_len;
 672
 673         end = window_pos + block_size;
 674         while (window_pos < end) {
 675                 main_element = read_huffsym_using_maintree(istream, tables);
 676                 if (main_element < LZX_NUM_CHARS) {
 677                         /* literal: 0 to LZX_NUM_CHARS - 1 */
 678                         window[window_pos++] = main_element;
 679                 } else {
 680                         /* match: LZX_NUM_CHARS to num_main_syms - 1 */
 681                         match_len = lzx_decode_match(main_element,
 682                                                      block_type,
 683                                                      end - window_pos,
 684                                                      window,
 685                                                      window_pos,
 686                                                      tables,
 687                                                      queue,
 688                                                      istream);
 689                         if (unlikely(match_len < 0))
 690                                 return match_len;
 691                         window_pos += match_len;
 692                 }
 693         }
 694         return 0;
 695 }
 696
 697 static int
 698 lzx_decompress(const void *compressed_data, size_t compressed_size,
 699                void *uncompressed_data, size_t uncompressed_size,
 700                void *_ctx)
 701 {
 702         struct lzx_decompressor *ctx = _ctx;
 703         struct input_bitstream istream;
 704         struct lzx_lru_queue queue;
 705         unsigned window_pos;
 706         unsigned block_size;
 707         unsigned block_type;
 708         int ret;
 709         bool e8_preprocessing_done;
 710
 711         LZX_DEBUG("compressed_data = %p, compressed_size = %zu, "
 712                   "uncompressed_data = %p, uncompressed_size = %zu, "
 713                   "max_window_size=%u).",
 714                   compressed_data, compressed_size,
 715                   uncompressed_data, uncompressed_size,
 716                   ctx->max_window_size);
 717
 718         if (uncompressed_size > ctx->max_window_size) {
 719                 LZX_DEBUG("Uncompressed size of %zu exceeds "
 720                           "window size of %u!",
 721                           uncompressed_size, ctx->max_window_size);
 722                 return -1;
 723         }
 724
 725         memset(ctx->tables.maintree_lens, 0, sizeof(ctx->tables.maintree_lens));
 726         memset(ctx->tables.lentree_lens, 0, sizeof(ctx->tables.lentree_lens));
 727         lzx_lru_queue_init(&queue);
 728         init_input_bitstream(&istream, compressed_data, compressed_size);
 729
 730         e8_preprocessing_done = false; /* Set to true if there may be 0xe8 bytes
 731                                           in the uncompressed data. */
 732
 733         /* The compressed data will consist of one or more blocks.  The
 734          * following loop decompresses one block, and it runs until there all
 735          * the compressed data has been decompressed, so there are no more
 736          * blocks.  */
 737
 738         for (window_pos = 0;
 739              window_pos < uncompressed_size;
 740              window_pos += block_size)
 741         {
 742                 LZX_DEBUG("Reading block header.");
 743                 ret = lzx_read_block_header(&istream, ctx->num_main_syms,
 744                                             ctx->max_window_size, &block_size,
 745                                             &block_type, &ctx->tables, &queue);
 746                 if (ret)
 747                         return ret;
 748
 749                 LZX_DEBUG("block_size = %u, window_pos = %u",
 750                           block_size, window_pos);
 751
 752                 if (block_size > uncompressed_size - window_pos) {
 753                         LZX_DEBUG("Expected a block size of at "
 754                                   "most %zu bytes (found %u bytes)",
 755                                   uncompressed_size - window_pos, block_size);
 756                         return -1;
 757                 }
 758
 759                 switch (block_type) {
 760                 case LZX_BLOCKTYPE_VERBATIM:
 761                 case LZX_BLOCKTYPE_ALIGNED:
 762                         if (block_type == LZX_BLOCKTYPE_VERBATIM)
 763                                 LZX_DEBUG("LZX_BLOCKTYPE_VERBATIM");
 764                         else
 765                                 LZX_DEBUG("LZX_BLOCKTYPE_ALIGNED");
 766                         ret = lzx_decompress_block(block_type,
 767                                                    block_size,
 768                                                    uncompressed_data,
 769                                                    window_pos,
 770                                                    &ctx->tables,
 771                                                    &queue,
 772                                                    &istream);
 773                         if (ret)
 774                                 return ret;
 775
 776                         if (ctx->tables.maintree_lens[0xe8] != 0)
 777                                 e8_preprocessing_done = true;
 778                         break;
 779                 case LZX_BLOCKTYPE_UNCOMPRESSED:
 780                         LZX_DEBUG("LZX_BLOCKTYPE_UNCOMPRESSED");
 781                         if (istream.data_bytes_left < block_size) {
 782                                 LZX_DEBUG("Unexpected end of input when "
 783                                           "reading %u bytes from LZX bitstream "
 784                                           "(only have %u bytes left)",
 785                                           block_size, istream.data_bytes_left);
 786                                 return -1;
 787                         }
 788                         memcpy(&((u8*)uncompressed_data)[window_pos], istream.data,
 789                                block_size);
 790                         istream.data += block_size;
 791                         istream.data_bytes_left -= block_size;
 792                         /* Re-align bitstream if an odd number of bytes were
 793                          * read.  */
 794                         if (istream.data_bytes_left && (block_size & 1)) {
 795                                 istream.data_bytes_left--;
 796                                 istream.data++;
 797                         }
 798                         e8_preprocessing_done = true;
 799                         break;
 800                 }
 801         }
 802         if (e8_preprocessing_done)
 803                 lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size);
 804         return 0;
 805 }
 806
 807 static void
 808 lzx_free_decompressor(void *_ctx)
 809 {
 810         struct lzx_decompressor *ctx = _ctx;
 811
 812         ALIGNED_FREE(ctx);
 813 }
 814
 815 static int
 816 lzx_create_decompressor(size_t max_window_size,
 817                         const struct wimlib_decompressor_params_header *params,
 818                         void **ctx_ret)
 819 {
 820         struct lzx_decompressor *ctx;
 821
 822         if (!lzx_window_size_valid(max_window_size))
 823                 return WIMLIB_ERR_INVALID_PARAM;
 824
 825         ctx = ALIGNED_MALLOC(sizeof(struct lzx_decompressor),
 826                              DECODE_TABLE_ALIGNMENT);
 827         if (ctx == NULL)
 828                 return WIMLIB_ERR_NOMEM;
 829
 830         ctx->max_window_size = max_window_size;
 831         ctx->num_main_syms = lzx_get_num_main_syms(max_window_size);
 832
 833         *ctx_ret = ctx;
 834         return 0;
 835 }
 836
 837 const struct decompressor_ops lzx_decompressor_ops = {
 838         .create_decompressor = lzx_create_decompressor,
 839         .decompress          = lzx_decompress,
 840         .free_decompressor   = lzx_free_decompressor,
 841 };