+++ /dev/null
-/*
- * xpress-decompress.c
- *
- * A very fast decompressor for XPRESS (Huffman version).
- */
-
-/*
- *
- * Copyright (C) 2012, 2013 Eric Biggers
- *
- * This file 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 3 of the License, or (at your option) any
- * later version.
- *
- * This file 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 this file; if not, see http://www.gnu.org/licenses/.
- */
-
-
-/*
- * The XPRESS compression format is an LZ77 and Huffman-code based algorithm.
- * That means it is fairly similar to LZX compression, but XPRESS is 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 code used for match/literal headers. In contrast with more
- * complicated formats such as DEFLATE and LZX, this is the only Huffman code
- * that is used for the entirety of the XPRESS 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 represent the corresponding literal bytes. Values 256 through 511
- * represent matches and may require extra bits or bytes to be read to get the
- * match offset and match length.
- *
- * The trickiest part is probably the way in which literal bytes for match
- * lengths are interleaved in 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 the implementation in WIMGAPI. However, wimlib's
- * decompressor in this file currently does not care if this extra symbol is
- * there or not.
- */
-
-#ifdef HAVE_CONFIG_H
-# include "config.h"
-#endif
-
-#include "wimlib/decompressor_ops.h"
-#include "wimlib/decompress_common.h"
-#include "wimlib/error.h"
-#include "wimlib/xpress.h"
-
-/* This value is chosen for fast decompression. */
-#define XPRESS_TABLEBITS 12
-
-/* Decode the matches and literal bytes in a region of XPRESS-encoded data. */
-static int
-xpress_decode_window(struct input_bitstream *istream, const u16 *decode_table,
- u8 *window, unsigned window_size)
-{
- u8 *window_ptr = window;
- u8 *window_end = &window[window_size];
- unsigned sym;
- unsigned match_len;
- unsigned offset_high_bit;
- unsigned match_offset;
-
- while (window_ptr != window_end) {
-
- sym = read_huffsym(istream, decode_table,
- XPRESS_TABLEBITS, XPRESS_MAX_CODEWORD_LEN);
- if (sym < XPRESS_NUM_CHARS) {
- /* Literal */
- *window_ptr++ = sym;
- continue;
- }
-
- /* Match */
- match_len = sym & 0xf;
- offset_high_bit = (sym >> 4) & 0xf;
-
- bitstream_ensure_bits(istream, 16);
-
- match_offset = (1 << offset_high_bit) |
- bitstream_pop_bits(istream, offset_high_bit);
-
- if (match_len == 0xf) {
- match_len += bitstream_read_byte(istream);
- if (match_len == 0xf + 0xff)
- match_len = bitstream_read_u16(istream);
- }
- match_len += XPRESS_MIN_MATCH_LEN;
-
- if (unlikely(match_offset > window_ptr - window))
- return -1;
-
- if (unlikely(match_len > window_end - window_ptr))
- return -1;
-
- lz_copy(window_ptr, match_len, match_offset, window_end,
- XPRESS_MIN_MATCH_LEN);
-
- window_ptr += match_len;
- }
- return 0;
-}
-
-static int
-xpress_decompress(const void *compressed_data, size_t compressed_size,
- void *uncompressed_data, size_t uncompressed_size, void *_ctx)
-{
- const u8 *cdata = compressed_data;
- u8 lens[XPRESS_NUM_SYMBOLS];
- u8 *lens_p;
- u16 decode_table[(1 << XPRESS_TABLEBITS) + 2 * XPRESS_NUM_SYMBOLS]
- _aligned_attribute(DECODE_TABLE_ALIGNMENT);
- struct input_bitstream istream;
-
- /* XPRESS uses only one Huffman code. 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_size < XPRESS_NUM_SYMBOLS / 2)
- return -1;
-
- lens_p = lens;
- for (unsigned i = 0; i < XPRESS_NUM_SYMBOLS / 2; i++) {
- *lens_p++ = cdata[i] & 0xf;
- *lens_p++ = cdata[i] >> 4;
- }
-
- if (make_huffman_decode_table(decode_table, XPRESS_NUM_SYMBOLS,
- XPRESS_TABLEBITS, lens,
- XPRESS_MAX_CODEWORD_LEN))
- return -1;
-
- init_input_bitstream(&istream, cdata + XPRESS_NUM_SYMBOLS / 2,
- compressed_size - XPRESS_NUM_SYMBOLS / 2);
-
- return xpress_decode_window(&istream, decode_table,
- uncompressed_data, uncompressed_size);
-}
-
-static int
-xpress_create_decompressor(size_t max_block_size, void **dec_ret)
-{
- if (max_block_size > XPRESS_MAX_OFFSET + 1)
- return WIMLIB_ERR_INVALID_PARAM;
-
- return 0;
-}
-
-const struct decompressor_ops xpress_decompressor_ops = {
- .create_decompressor = xpress_create_decompressor,
- .decompress = xpress_decompress,
-};
projects / wimlib / blobdiff