/*
* xpress-decompress.c
*
- * XPRESS decompression routines.
+ * A very fast decompressor for XPRESS (Huffman version).
*/
/*
*
- * Copyright (C) 2012 Eric Biggers
+ * Copyright (C) 2012, 2013 Eric Biggers
*
* This file is part of wimlib, a library for working with WIM files.
*
*/
-
/*
- * 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 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
* 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
+ * 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 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.
+ * 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 fact that literal bytes for match lengths
- * are encoded "separately" from the bitstream.
+ * 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 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.
+ * "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."
*
- * However, wimlib's decompressor in this file currently does not care if this
- * extra symbol is there or not.
+ * 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.
*/
-#include "util.h"
-#include "xpress.h"
-#include "wimlib.h"
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
-#define XPRESS_DECOMP
-#include "decompress.h"
+#include "wimlib/decompressor_ops.h"
+#include "wimlib/decompress_common.h"
+#include "wimlib/error.h"
+#include "wimlib/xpress.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.
- *
- * Returns the match length, or -1 on error.
- */
-static int xpress_decode_match(unsigned huffsym, unsigned window_pos,
- unsigned window_len, u8 window[],
- struct input_bitstream *istream)
+/* 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_bsr;
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 ret;
- match_offset |= (1 << offset_bsr);
-
- if (len_hdr == 0xf) {
- ret = bitstream_read_byte(istream);
- if (ret < 0)
- return ret;
- match_len = ret;
- if (match_len == 0xff) {
- ret = bitstream_read_byte(istream);
- if (ret < 0)
- return ret;
- match_len = ret;
-
- ret = bitstream_read_byte(istream);
- if (ret < 0)
- return ret;
-
- match_len |= (ret << 8);
- } else {
- match_len += 0xf;
+
+ 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;
}
- } 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 */
+ match_len = sym & 0xf;
+ offset_bsr = (sym >> 4) & 0xf;
- match_dest = window + window_pos;
- match_src = match_dest - match_offset;
+ bitstream_ensure_bits(istream, 16);
- if (window_pos + match_len > window_len) {
- ERROR("XPRESS decompression error: match of length %d "
- "bytes overflows window", match_len);
- return -1;
- }
+ match_offset = (1 << offset_bsr) |
+ bitstream_pop_bits(istream, offset_bsr);
- 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;
- }
+ 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;
- for (i = 0; i < match_len; i++)
- match_dest[i] = match_src[i];
+ if (unlikely(match_offset > window_ptr - window))
+ return -1;
- return match_len;
-}
+ if (unlikely(match_len > window_end - window_ptr))
+ return -1;
-/* Decodes the Huffman-encoded matches and literal bytes in a block of
- * XPRESS-encoded data. */
-static int xpress_decompress_block(struct input_bitstream *istream,
- u8 uncompressed_data[],
- unsigned uncompressed_len,
- const u8 lens[],
- const u16 decode_table[])
-{
- unsigned curpos;
- unsigned huffsym;
- int ret;
- int match_len;
-
- curpos = 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)
- return ret;
-
- 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 < 0)
- return match_len;
- curpos += match_len;
- }
+ lz_copy(window_ptr, match_len, match_offset, window_end);
+
+ window_ptr += match_len;
}
return 0;
}
-
-int xpress_decompress(const void *__compressed_data, unsigned compressed_len,
- void *uncompressed_data, unsigned uncompressed_len)
+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];
- 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);
+ u16 decode_table[(1 << XPRESS_TABLEBITS) + 2 * XPRESS_NUM_SYMBOLS]
+ _aligned_attribute(DECODE_TABLE_ALIGNMENT);
+ struct input_bitstream istream;
- /* XPRESS uses only one Huffman tree. It contains 512 symbols, and the
+ /* 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_len < XPRESS_NUM_SYMBOLS / 2)
+ * in the first 256 bytes of the compressed data. */
+ if (compressed_size < XPRESS_NUM_SYMBOLS / 2)
return -1;
- for (i = 0; i < XPRESS_NUM_SYMBOLS / 2; i++) {
- *lens_p++ = compressed_data[i] & 0xf;
- *lens_p++ = compressed_data[i] >> 4;
+ lens_p = lens;
+ for (unsigned i = 0; i < XPRESS_NUM_SYMBOLS / 2; i++) {
+ *lens_p++ = cdata[i] & 0xf;
+ *lens_p++ = cdata[i] >> 4;
}
- ret = make_huffman_decode_table(decode_table, XPRESS_NUM_SYMBOLS,
- XPRESS_TABLEBITS, lens,
- XPRESS_MAX_CODEWORD_LEN);
- if (ret != 0)
- return ret;
+ if (make_huffman_decode_table(decode_table, XPRESS_NUM_SYMBOLS,
+ XPRESS_TABLEBITS, lens,
+ XPRESS_MAX_CODEWORD_LEN))
+ return -1;
- init_input_bitstream(&istream, compressed_data + XPRESS_NUM_SYMBOLS / 2,
- compressed_len - XPRESS_NUM_SYMBOLS / 2);
+ init_input_bitstream(&istream, cdata + XPRESS_NUM_SYMBOLS / 2,
+ compressed_size - XPRESS_NUM_SYMBOLS / 2);
- return xpress_decompress_block(&istream, uncompressed_data,
- uncompressed_len, lens,
- decode_table);
+ 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,
+};
git://wimlib.net / wimlib / blobdiff