*/
-
/*
- * 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,
*
* 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.
- *
- * 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.
*/
#ifdef HAVE_CONFIG_H
#endif
#include "wimlib.h"
-#include "wimlib/assert.h"
-#define XPRESS_DECOMP
#include "wimlib/decompress.h"
-#include "wimlib/util.h"
#include "wimlib/xpress.h"
/*
- * Decodes a symbol @huffsym that begins an XPRESS match.
+ * Decodes a symbol @sym 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.
+ * Returns the match length, or -1 if the data is invalid.
*/
static int
-xpress_decode_match(unsigned huffsym, unsigned window_pos,
- unsigned window_len, u8 window[restrict],
+xpress_decode_match(unsigned sym, input_idx_t window_pos,
+ input_idx_t window_len, u8 window[restrict],
struct input_bitstream * restrict istream)
{
- unsigned match_len;
- unsigned match_offset;
- u8 match_sym = (u8)huffsym;
- u8 len_hdr = match_sym & 0xf;
- u8 offset_bsr = match_sym >> 4;
+
+ u8 len_hdr;
+ u8 offset_bsr;
int ret;
u8 *match_dest;
u8 *match_src;
unsigned i;
+ unsigned match_len;
+ unsigned match_offset;
+
+ sym -= XPRESS_NUM_CHARS;
+ len_hdr = sym & 0xf;
+ offset_bsr = sym >> 4;
+
+ if (bitstream_ensure_bits(istream, 16))
+ return -1;
- ret = bitstream_read_bits(istream, offset_bsr, &match_offset);
- if (ret)
- return ret;
- match_offset |= (1 << offset_bsr);
+ match_offset = (1U << offset_bsr) | bitstream_pop_bits(istream, offset_bsr);
if (len_hdr == 0xf) {
ret = bitstream_read_byte(istream);
if (ret < 0)
return ret;
match_len = ret;
- if (match_len == 0xff) {
+ if (unlikely(match_len == 0xff)) {
ret = bitstream_read_byte(istream);
if (ret < 0)
return ret;
} else {
match_len = len_hdr;
}
- match_len += XPRESS_MIN_MATCH;
+ match_len += XPRESS_MIN_MATCH_LEN;
- /* 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. */
- if (window_pos + match_len > window_len) {
- DEBUG("XPRESS decompression error: match of length %u "
- "bytes overflows window", match_len);
+ /* Verify the match is in bounds, then copy its data to the the current
+ * position. */
+
+ if (window_pos + match_len > window_len)
return -1;
- }
- if (match_offset > window_pos) {
- DEBUG("XPRESS decompression error: match of length %u bytes "
- "references data before window (match_offset = %u, "
- "window_pos = %u)", match_len, match_offset, window_pos);
+ if (match_offset > window_pos)
return -1;
- }
match_dest = window + window_pos;
match_src = match_dest - match_offset;
return match_len;
}
-/* Decodes the Huffman-encoded matches and literal bytes in a block of
- * XPRESS-encoded data. */
+/* Decodes the Huffman-encoded matches and literal bytes in a region of
+ * XPRESS-encoded data. */
static int
-xpress_decompress_block(struct input_bitstream * restrict istream,
- u8 uncompressed_data[restrict],
- unsigned uncompressed_len,
- const u8 lens[restrict],
- const u16 decode_table[restrict])
+xpress_lz_decode(struct input_bitstream * restrict istream,
+ u8 uncompressed_data[restrict],
+ unsigned uncompressed_len,
+ const u8 lens[restrict],
+ const u16 decode_table[restrict])
{
- 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)
- return ret;
+ input_idx_t curpos;
+ unsigned match_len;
+
+ for (curpos = 0; curpos < uncompressed_len; curpos += match_len) {
+ unsigned sym;
+ int ret;
+
+ if (unlikely(bitstream_ensure_bits(istream, 16)))
+ return -1;
- if (huffsym < XPRESS_NUM_CHARS) {
- uncompressed_data[curpos++] = huffsym;
+ if (unlikely(read_huffsym(istream, decode_table, lens,
+ XPRESS_NUM_SYMBOLS, XPRESS_TABLEBITS,
+ &sym, XPRESS_MAX_CODEWORD_LEN)))
+ return -1;
+
+ if (sym < XPRESS_NUM_CHARS) {
+ /* Literal */
+ uncompressed_data[curpos] = sym;
+ match_len = 1;
} else {
- match_len = xpress_decode_match(huffsym,
- curpos,
- uncompressed_len,
- uncompressed_data,
- istream);
- if (match_len < 0)
- return match_len;
- curpos += match_len;
+ /* Match */
+ ret = xpress_decode_match(sym,
+ curpos,
+ uncompressed_len,
+ uncompressed_data,
+ istream);
+ if (unlikely(ret < 0))
+ return -1;
+ match_len = ret;
}
}
return 0;
/* API function documented in wimlib.h */
WIMLIBAPI int
-wimlib_xpress_decompress(const void * restrict _compressed_data, unsigned compressed_len,
- void * restrict uncompressed_data, unsigned uncompressed_len)
+wimlib_xpress_decompress(const void * const restrict _compressed_data,
+ const unsigned compressed_len,
+ void * const restrict uncompressed_data,
+ const unsigned uncompressed_len)
{
+ const u8 *compressed_data = _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;
- 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
+ /* 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) {
- DEBUG("xpress_decompress(): Compressed length too short!");
+ * in the first 256 bytes of the compressed data. */
+ if (compressed_len < XPRESS_NUM_SYMBOLS / 2)
return -1;
- }
- for (i = 0; i < XPRESS_NUM_SYMBOLS / 2; i++) {
+ lens_p = lens;
+ for (unsigned 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)
- 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);
- return xpress_decompress_block(&istream, uncompressed_data,
- uncompressed_len, lens,
- decode_table);
+ return xpress_lz_decode(&istream, uncompressed_data,
+ uncompressed_len, lens, decode_table);
}
git://wimlib.net / wimlib / blobdiff