/*
* xpress-decompress.c
*
- * XPRESS decompression routines.
+ * A very fast decompressor for XPRESS (Huffman version).
*/
/*
# include "config.h"
#endif
-#include "wimlib.h"
#include "wimlib/decompressor_ops.h"
#include "wimlib/decompress_common.h"
+#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, input_idx_t window_pos,
- input_idx_t 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)
{
-
- u8 len_hdr;
- u8 offset_bsr;
- u8 *match_dest;
- u8 *match_src;
- unsigned i;
+ 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);
-
- match_offset = (1U << offset_bsr) | bitstream_pop_bits(istream, offset_bsr);
+ while (window_ptr != window_end) {
- 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;
-
- /* Verify the match is in bounds, then copy its data to the current
- * position. */
-
- if (window_pos + match_len > window_len)
- return -1;
-
- if (match_offset > window_pos)
- return -1;
+ /* 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);
- for (i = 0; i < match_len; i++)
- match_dest[i] = match_src[i];
+ 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 u8 lens[restrict],
- const u16 decode_table[restrict])
-{
- input_idx_t 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;
- bitstream_ensure_bits(istream, 16);
+ lz_copy(window_ptr, match_len, match_offset, window_end);
- sym = read_huffsym(istream, decode_table, lens,
- XPRESS_NUM_SYMBOLS, 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;
- }
+ 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, 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 = {
- .decompress = xpress_decompress,
+ .create_decompressor = xpress_create_decompressor,
+ .decompress = xpress_decompress,
};
git://wimlib.net / wimlib / blobdiff