* of the bits within the 16-bit coding units is such that the first bit is the
* high-order bit and the last bit is the low-order bit.
*
- * From these two logical bitstreams, a LZMS decompressor can reconstitute the
+ * From these two logical bitstreams, an LZMS decompressor can reconstitute the
* series of items that make up the LZMS data representation. Each such item
* may be a literal byte or a match. Matches may be either traditional LZ77
* matches or "delta" matches, either of which can have its offset encoded
* sequence of bytes beginning at the current position and extending for the
* length is exactly equal to the equal-length sequence of bytes at the offset
* back in the window. On the other hand, a delta match consists of a length,
- * raw offset, and power. It asserts that the sequence of bytes of beginning at
+ * raw offset, and power. It asserts that the sequence of bytes beginning at
* the current position and extending for the length is equal to the bytewise
* sum of the two equal-length sequences of bytes (2**power) and (raw_offset *
* 2**power) bytes before the current position, minus bytewise the sequence of
* filled in with the next 16 bits from the forwards bitstream.
*
* To decode each bit, the range decoder requires a probability that is
- * logically a real number between 0 and 1. Multiplying this
- * probability by the current range and taking the floor gives the bound between
- * the 0-bit region of the range and the 1-bit region of the range. However, in
- * LZMS, probabilities are restricted to values of n/64 where n is an integer is
+ * logically a real number between 0 and 1. Multiplying this probability by the
+ * current range and taking the floor gives the bound between the 0-bit region
+ * of the range and the 1-bit region of the range. However, in LZMS,
+ * probabilities are restricted to values of n/64 where n is an integer is
* between 1 and 63 inclusively, so the implementation may use integer
* operations instead. Following calculation of the bound, if the current code
* is in the 0-bit region, the new range becomes the current code and the
* decoded bit is 0; otherwise, the bound must be subtracted from both the range
* and the code, and the decoded bit is 1. More information about range coding
- * can be found https://en.wikipedia.org/wiki/Range_encoding. Furthermore, note
- * that the LZMA format also uses range coding and has public domain code
+ * can be found at https://en.wikipedia.org/wiki/Range_encoding. Furthermore,
+ * note that the LZMA format also uses range coding and has public domain code
* available for it.
*
* The probability used to range-decode each bit must be taken from a table, of
* bitstream. For this, there are 5 different Huffman codes used:
*
* - The literal code, used for decoding literal bytes. Each of the 256
- * symbols represents literal byte. This code must be rebuilt whenever 1024
- * symbols have been decoded with it.
+ * symbols represents a literal byte. This code must be rebuilt whenever
+ * 1024 symbols have been decoded with it.
*
* - The LZ offset code, used for decoding the offsets of standard LZ77
* matches. Each symbol represents a position slot, which corresponds to a
*
* Codewords in all the LZMS Huffman codes are limited to 15 bits. If the
* canonical code for a given set of symbol frequencies has any codewords longer
- * than 15 bits, all frequencies must be divided by 2, rounding up, and the code
- * construction must be attempted again.
+ * than 15 bits, then all frequencies must be divided by 2, rounding up, and the
+ * code construction must be attempted again.
*
- * A LZMS-compressed block seemingly cannot have a size greater than or equal to
- * the original uncompressed size. In such cases the block must be stored
+ * A LZMS-compressed block seemingly cannot have a compressed size greater than
+ * or equal to the uncompressed size. In such cases the block must be stored
* uncompressed.
*
* After all LZMS items have been decoded, the data must be postprocessed to
{
int ret;
- /* XXX: This implementation that makes use of code already implemented
- * for the XPRESS and LZX compression formats. However, since for the
+ /* XXX: This implementation makes use of code already implemented for
+ * the XPRESS and LZX compression formats. However, since for the
* adaptive codes used in LZMS we don't actually need the explicit codes
* themselves, only the decode tables, it may be possible to optimize
* this by somehow directly building or updating the Huffman decode
return 0;
}
-/* Validate a LZ match and copy it to the output buffer. */
+/* Validate an LZ match and copy it to the output buffer. */
static int
lzms_copy_lz_match(struct lzms_decompressor *ctx, u32 length, u32 offset)
{
for (int i = LZMS_NUM_RECENT_OFFSETS - 1; i >= 0; i--)
ctx->recent_lz_offsets[i + 1] = ctx->recent_lz_offsets[i];
ctx->recent_lz_offsets[0] = ctx->prev_lz_offset;
-
}
if (ctx->prev_delta_offset != 0) {
dec->sym_freqs[i] = 1;
}
-/* Prepare to decode items from a LZMS-compressed block. */
+/* Prepare to decode items from an LZMS-compressed block. */
static void
lzms_init_decompressor(struct lzms_decompressor *ctx,
const void *cdata, unsigned clen,
/* Initialize position and length slot bases if not done already. */
lzms_init_slot_bases();
- /* Like in other compression formats such as LZX and DEFLATE, match
- * offsets in LZMS are represented as a position slot, which corresponds
- * to a fixed lesser or equal match offset, followed by a
- * position-slot-dependent number of extra bits that gives an additional
- * offset from that position slot. Because the full number of position
- * slots may exceed the length of the compressed block, here we
- * calculate the number of position slots that will actually be used in
- * the compressed representation. */
+ /* Calculate the number of position slots needed for this compressed
+ * block. */
num_position_slots = lzms_get_position_slot_raw(ulen - 1) + 1;
LZMS_DEBUG("Using %u position slots", num_position_slots);
LZMS_DELTA_POWER_CODE_REBUILD_FREQ);
- /* Initialize range decoders (all of which wrap around the same
- * lzms_range_decoder_raw). */
+ /* Initialize range decoders, all of which wrap around the same
+ * lzms_range_decoder_raw. */
lzms_init_range_decoder(&ctx->main_range_decoder,
&ctx->rd, LZMS_NUM_MAIN_STATES);
lzms_init_range_decoder(&ctx->delta_repeat_match_range_decoders[i],
&ctx->rd, LZMS_NUM_DELTA_REPEAT_MATCH_STATES);
-
/* Initialize the LRU queue for recent match offsets. */
for (size_t i = 0; i < LZMS_NUM_RECENT_OFFSETS + 1; i++)
ctx->recent_lz_offsets[i] = i + 1;
git://wimlib.net / wimlib / commitdiff