+++ /dev/null
-/*
- * xpress-decomp.c
- *
- * XPRESS decompression routines.
- */
-
-/*
- *
- * 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 General Public License as published by the Free
- * Software Foundation; either version 3 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 General Public License for more
- * details.
- *
- * You should have received a copy of the GNU General Public License
- * along with wimlib; if not, see http://www.gnu.org/licenses/.
- */
-
-
-
-/*
- * The XPRESS compression format is a LZ77 and Huffman-code based algorithm.
- * That means it is quite similar to LZX compression, but XPRESS is slightly
- * simpler, so it is a little faster to compress and decompress.
- *
- * The XPRESS compression format is mostly documented in a file called "[MS-XCA]
- * Xpress Compression Algorithm". In the MSDN library, it can currently be
- * found under Open Specifications => Protocols => Windows Protocols => Windows
- * Server Protocols => [MS-XCA] Xpress Compression Algorithm". The format in
- * WIMs is specifically the algorithm labeled as the "LZ77+Huffman Algorithm"
- * (there apparently are some other versions of XPRESS as well).
- *
- * If you are already familiar with the LZ77 algorithm and Huffman coding, the
- * XPRESS format is fairly simple. The compressed data begins with 256 bytes
- * that contain 512 4-bit integers that are the lengths of the symbols in the
- * Huffman tree used for decoding compressed literals. This is the only Huffman
- * tree that is used for the entirety of the compressed data, and the codeword
- * lengths are not encoded with a pretree.
- *
- * The rest of the compressed data is Huffman-encoded symbols. Values 0 through
- * 255 are literal bytes. Values 256 through 511 are matches and may require
- * extra bits or bytes to be read to get the match offset and match length.
- *
- * There is no notion of a "compressed block" in the XPRESS format, so in the
- * XPRESS format, each WIM chunk (32768 bytes) will always use only one Huffman
- * tree.
- *
- * The trickiest part is probably the fact that literal bytes for match lengths
- * are encoded "separately" from the bitstream.
- *
- * Also, a caveat--- according to Microsoft's documentation for XPRESS,
- *
- * "Some implementation of the decompression algorithm expect an extra
- * symbol to mark the end of the data. Specifically, some implementations
- * fail during decompression if the Huffman symbol 256 is not found after
- * the actual data."
- *
- * This is the case for WIM files--- in we must write this extra symbol "256" at
- * the end. Otherwise Microsoft's software will fail to decompress the
- * XPRESS-compressed data.
- *
- * Howeve, wimlib's decompressor in xpress-decomp.c currently does not care if
- * this extra symbol is there or not.
- */
-
-#include "util.h"
-#include "xpress.h"
-#include "wimlib.h"
-
-#define XPRESS_DECOMP
-#include "decomp.h"
-
-
-/*
- * Decodes a symbol @huffsym that begins an XPRESS match.
- *
- * The low 8 bits of the symbol are divided into:
- *
- * bits 0-3: length header
- * bits 4-7: index of high-order bit of match offset
- *
- * Note: taking the low 8 bits of the symbol is the same as subtracting 256, the
- * number of symbols reserved for literals.
- */
-static int xpress_decode_match(int huffsym, unsigned window_pos,
- unsigned window_len, u8 window[],
- struct input_bitstream *istream)
-{
- unsigned match_len;
- unsigned match_offset;
- u8 match_sym = (u8)huffsym;
- u8 len_hdr = match_sym & 0xf;
- u8 offset_bsr = match_sym >> 4;
- int ret;
- u8 *match_dest;
- u8 *match_src;
- unsigned i;
-
- ret = bitstream_read_bits(istream, offset_bsr, &match_offset);
- if (ret != 0)
- return -1;
- match_offset |= (1 << offset_bsr);
-
- if (len_hdr == 0xf) {
- ret = bitstream_read_byte(istream);
- if (ret == -1)
- return -1;
- match_len = ret;
- if (match_len == 0xff) {
- ret = bitstream_read_byte(istream);
- if (ret == -1)
- return -1;
- match_len = ret;
-
- ret = bitstream_read_byte(istream);
- if (ret == -1)
- return -1;
-
- match_len |= (ret << 8);
- if (match_len < 0xf)
- return -1;
- } else {
- match_len += 0xf;
- }
- } else {
- match_len = len_hdr;
- }
- match_len += XPRESS_MIN_MATCH;
-
- /* 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 (window_pos + match_len > window_len) {
- ERROR("XPRESS decompression error: match of length %d "
- "bytes overflows window", match_len);
- return -1;
- }
-
- if (match_src < window) {
- ERROR("XPRESS decompression error: match of length %d bytes "
- "references data before window (match_offset = %d, "
- "window_pos = %d)", match_len, match_offset, window_pos);
- return -1;
- }
-
- for (i = 0; i < match_len; i++)
- match_dest[i] = match_src[i];
-
- return match_len;
-}
-
-/* Decodes the Huffman-encoded matches and literal bytes in a block of
- * XPRESS-encoded data. */
-static int xpress_decompress_literals(struct input_bitstream *istream,
- u8 uncompressed_data[],
- unsigned uncompressed_len,
- const u8 lens[],
- const u16 decode_table[])
-{
- unsigned curpos = 0;
- unsigned huffsym;
- int match_len;
- int ret = 0;
-
- while (curpos < uncompressed_len) {
- ret = read_huffsym(istream, decode_table, lens,
- XPRESS_NUM_SYMBOLS, XPRESS_TABLEBITS,
- &huffsym, XPRESS_MAX_CODEWORD_LEN);
- if (ret != 0)
- break;
-
- if (huffsym < XPRESS_NUM_CHARS) {
- uncompressed_data[curpos++] = huffsym;
- } else {
- match_len = xpress_decode_match(huffsym,
- curpos,
- uncompressed_len,
- uncompressed_data,
- istream);
- if (match_len == -1) {
- ret = 1;
- break;
- }
- curpos += match_len;
- }
- }
- return ret;
-}
-
-
-int xpress_decompress(const void *__compressed_data, unsigned compressed_len,
- void *uncompressed_data, unsigned uncompressed_len)
-{
- u8 lens[XPRESS_NUM_SYMBOLS];
- u16 decode_table[(1 << XPRESS_TABLEBITS) + 2 * XPRESS_NUM_SYMBOLS];
- struct input_bitstream istream;
- u8 *lens_p;
- const u8 *compressed_data;
- unsigned i;
- int ret;
-
- compressed_data = __compressed_data;
- lens_p = lens;
-
- DEBUG2("compressed_len = %d, uncompressed_len = %d",
- compressed_len, uncompressed_len);
-
- /* XPRESS uses only one Huffman tree. It contains 512 symbols, and the
- * code lengths of these symbols are given literally as 4-bit integers
- * in the first 256 bytes of the compressed data.
- */
- if (compressed_len < XPRESS_NUM_SYMBOLS / 2)
- return WIMLIB_ERR_DECOMPRESSION;
-
- for (i = 0; i < XPRESS_NUM_SYMBOLS / 2; i++) {
- *lens_p++ = compressed_data[i] & 0xf;
- *lens_p++ = compressed_data[i] >> 4;
- }
-
- ret = make_huffman_decode_table(decode_table, XPRESS_NUM_SYMBOLS,
- XPRESS_TABLEBITS, lens,
- XPRESS_MAX_CODEWORD_LEN);
- if (ret != 0)
- return ret;
-
- init_input_bitstream(&istream, compressed_data + XPRESS_NUM_SYMBOLS / 2,
- compressed_len - XPRESS_NUM_SYMBOLS / 2);
-
- return xpress_decompress_literals(&istream, uncompressed_data,
- uncompressed_len, lens,
- decode_table);
-}
projects / wimlib / blobdiff