/*
* xpress-decompress.c
*
- * XPRESS decompression routines.
+ * A very fast decompressor for XPRESS (Huffman version).
*/
/*
*
* Copyright (C) 2012, 2013 Eric Biggers
*
- * This file is part of wimlib, a library for working with WIM files.
+ * 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.
*
- * 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
+ * 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 General Public License
- * along with wimlib; if not, see http://www.gnu.org/licenses/.
+ * 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/.
*/
#include "wimlib/error.h"
#include "wimlib/xpress.h"
-/*
- * 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
- *
- * Returns the match length, or -1 if the data is invalid.
- */
+/* 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_match(unsigned sym, u32 window_pos,
- u32 window_len, u8 window[restrict],
- struct input_bitstream * restrict istream)
+xpress_decode_window(struct input_bitstream *istream, const u16 *decode_table,
+ u8 *window, unsigned window_size)
{
- unsigned len_hdr;
- unsigned offset_bsr;
+ u8 *window_ptr = window;
+ u8 *window_end = &window[window_size];
+ unsigned sym;
unsigned match_len;
+ unsigned offset_bsr;
unsigned match_offset;
- sym -= XPRESS_NUM_CHARS;
- len_hdr = sym & 0xf;
- offset_bsr = sym >> 4;
-
- bitstream_ensure_bits(istream, 16);
+ while (window_ptr != window_end) {
- match_offset = (1U << offset_bsr) | bitstream_pop_bits(istream, offset_bsr);
-
- if (len_hdr == 0xf) {
- match_len = bitstream_read_byte(istream);
- if (unlikely(match_len == 0xff)) {
- match_len = bitstream_read_byte(istream);
- match_len |= (unsigned)bitstream_read_byte(istream) << 8;
- } else {
- match_len += 0xf;
+ 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_LEN;
- if (unlikely(match_len > window_len - window_pos))
- return -1;
+ /* Match */
+ match_len = sym & 0xf;
+ offset_bsr = (sym >> 4) & 0xf;
- if (unlikely(match_offset > window_pos))
- return -1;
+ bitstream_ensure_bits(istream, 16);
- lz_copy(&window[window_pos], match_len, match_offset,
- &window[window_len]);
+ match_offset = (1 << offset_bsr) |
+ bitstream_pop_bits(istream, offset_bsr);
- return match_len;
-}
+ 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;
-/* Decodes the Huffman-encoded matches and literal bytes in a region of
- * XPRESS-encoded data. */
-static int
-xpress_lz_decode(struct input_bitstream * restrict istream,
- u8 uncompressed_data[restrict],
- unsigned uncompressed_len,
- const u16 decode_table[restrict])
-{
- u32 curpos;
- unsigned match_len;
+ if (unlikely(match_offset > window_ptr - window))
+ return -1;
- for (curpos = 0; curpos < uncompressed_len; curpos += match_len) {
- unsigned sym;
- int ret;
+ if (unlikely(match_len > window_end - window_ptr))
+ return -1;
- sym = read_huffsym(istream, decode_table,
- XPRESS_TABLEBITS, XPRESS_MAX_CODEWORD_LEN);
- if (sym < XPRESS_NUM_CHARS) {
- /* Literal */
- uncompressed_data[curpos] = sym;
- match_len = 1;
- } else {
- /* Match */
- ret = xpress_decode_match(sym,
- curpos,
- uncompressed_len,
- uncompressed_data,
- istream);
- if (unlikely(ret < 0))
- return -1;
- match_len = ret;
- }
+ lz_copy(window_ptr, match_len, match_offset, window_end);
+
+ 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)
init_input_bitstream(&istream, cdata + XPRESS_NUM_SYMBOLS / 2,
compressed_size - XPRESS_NUM_SYMBOLS / 2);
- return xpress_lz_decode(&istream, uncompressed_data,
- uncompressed_size, decode_table);
+ return xpress_decode_window(&istream, decode_table,
+ uncompressed_data, uncompressed_size);
}
static int