*/
/*
- * Copyright (C) 2013 Eric Biggers
+ * Copyright (C) 2013, 2014 Eric Biggers
*
* This file is part of wimlib, a library for working with WIM files.
*
* is a container format from which the locations and sizes (both compressed and
* uncompressed) of the constituent blocks can be determined.
*
- * A LZMS-compressed block must be read in 16-bit little endian units from both
+ * An LZMS-compressed block must be read in 16-bit little endian units from both
* directions. One logical bitstream starts at the front of the block and
* proceeds forwards. Another logical bitstream starts at the end of the block
* and proceeds backwards. Bits read from the forwards bitstream constitute
* offset is 1, regardless of match length.
*
* For LZ matches, up to 3 repeat offsets are allowed, similar to some other
- * LZ-based formats such as LZX and LZMA. They must updated in a LRU fashion,
- * except for a quirk: updates to the queue must be delayed by one LZMS item,
- * except for the removal of a repeat match. As a result, 4 entries are
- * actually needed in the queue, even though it is only possible to decode
- * references to the first 3 at any given time. The queue must be initialized
- * to the offsets {1, 2, 3, 4}.
+ * LZ-based formats such as LZX and LZMA. They must updated in an LRU fashion,
+ * except for a quirk: inserting anything to the front of the queue must be
+ * delayed by one LZMS item. The reason for this is presumably that there is
+ * almost no reason to code the same match offset twice in a row, since you
+ * might as well have coded a longer match at that offset. For this same
+ * reason, it also is a requirement that when an offset in the queue is used,
+ * that offset is removed from the queue immediately (and made pending for
+ * front-insertion after the following decoded item), and everything to the
+ * right is shifted left one queue slot. This creates a need for an "overflow"
+ * fourth entry in the queue, even though it is only possible to decode
+ * references to the first 3 entries at any given time. The queue must be
+ * initialized to the offsets {1, 2, 3, 4}.
*
* Repeat delta matches are handled similarly, but for them there are two queues
* updated in lock-step: one for powers and one for raw offsets. The power
* 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
+ * matches. Each symbol represents an offset slot, which corresponds to a
* base value and some number of extra bits which must be read and added to
* the base value to reconstitute the full offset. The number of symbols in
- * this code is the number of position slots needed to represent all possible
+ * this code is the number of offset slots needed to represent all possible
* offsets in the uncompressed block. This code must be rebuilt whenever
* 1024 symbols have been decoded with it.
*
* symbols have been decoded with it.
*
* - The delta offset code, used for decoding the offsets of delta matches.
- * Each symbol corresponds to a position slot, which corresponds to a base
+ * Each symbol corresponds to an offset slot, which corresponds to a base
* value and some number of extra bits which must be read and added to the
* base value to reconstitute the full offset. The number of symbols in this
* code is equal to the number of symbols in the LZ offset code. This code
* have equal frequency. Following that, each code must be rebuilt whenever a
* certain number of symbols has been decoded with it.
*
- * In general, multiple valid Huffman codes can be constructed from a set of
- * symbol frequencies. Like other compression formats such as XPRESS, LZX, and
- * DEFLATE, the LZMS format solves this ambiguity by requiring that all Huffman
- * codes be constructed in canonical form. This form requires that same-length
- * codewords be lexicographically ordered the same way as the corresponding
- * symbols and that all shorter codewords lexicographically precede longer
- * codewords.
+ * Like other compression formats such as XPRESS, LZX, and DEFLATE, the LZMS
+ * format requires that all Huffman codes be constructed in canonical form.
+ * This form requires that same-length codewords be lexicographically ordered
+ * the same way as the corresponding symbols and that all shorter codewords
+ * lexicographically precede longer codewords. Such a code can be constructed
+ * directly from codeword lengths, although in LZMS this is not actually
+ * necessary because the codes are built using adaptive symbol frequencies.
*
- * 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, then all frequencies must be divided by 2, rounding up, and the
- * code construction must be attempted again.
+ * Even with the canonical code restriction, the same frequencies can be used to
+ * construct multiple valid Huffman codes. Therefore, the decompressor needs to
+ * construct the right one. Specifically, the LZMS format requires that the
+ * Huffman code be constructed as if the well-known priority queue algorithm is
+ * used and frequency ties are always broken in favor of leaf nodes. See
+ * make_canonical_huffman_code() in compress_common.c for more information.
*
- * A LZMS-compressed block seemingly cannot have a compressed size greater than
+ * Codewords in LZMS are guaranteed to not exceed 15 bits. The format otherwise
+ * places no restrictions on codeword length. Therefore, the Huffman code
+ * construction algorithm that a correct LZMS decompressor uses need not
+ * implement length-limited code construction. But if it does (e.g. by virtue
+ * of being shared among multiple compression algorithms), the details of how it
+ * does so are unimportant, provided that the maximum codeword length parameter
+ * is set to at least 15 bits.
+ *
+ * An 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.
*
# include "config.h"
#endif
-#include "wimlib.h"
#include "wimlib/compress_common.h"
#include "wimlib/decompressor_ops.h"
#include "wimlib/decompress_common.h"
+#include "wimlib/error.h"
#include "wimlib/lzms.h"
#include "wimlib/util.h"
* at a time, this needs to be 64 bits rather than 32 bits. */
u64 bitbuf;
- /* Number of bits in @bitbuf that are are used. */
+ /* Number of bits in @bitbuf that are used. */
unsigned num_filled_bits;
/* Pointer to the one past the next little-endian 16-bit integer in the
u8 lens[LZMS_MAX_NUM_SYMS];
/* The codeword of each symbol in the Huffman code. */
- u16 codewords[LZMS_MAX_NUM_SYMS];
+ u32 codewords[LZMS_MAX_NUM_SYMS];
/* A table for quickly decoding symbols encoded using the Huffman code.
*/
struct lzms_huffman_decoder delta_power_decoder;
struct lzms_huffman_decoder delta_offset_decoder;
- /* LRU (least-recently-used) queues for match information. */
- struct lzms_lru_queues lru;
+ /* LRU (least-recently-used) queues for match information. */
+ struct lzms_lru_queues lru;
/* Used for postprocessing. */
s32 last_target_usages[65536];
/* Load the probability entry corresponding to the current state. */
prob_entry = &dec->prob_entries[dec->state];
- /* Treat the number of zero bits in the most recently decoded
- * LZMS_PROBABILITY_MAX bits with this probability entry as the chance,
- * out of LZMS_PROBABILITY_MAX, that the next bit will be a 0. However,
- * don't allow 0% or 100% probabilities. */
- prob = prob_entry->num_recent_zero_bits;
- if (prob == LZMS_PROBABILITY_MAX)
- prob = LZMS_PROBABILITY_MAX - 1;
- else if (prob == 0)
- prob = 1;
+ /* Get the probability that the next bit is 0. */
+ prob = lzms_get_probability(prob_entry);
/* Decode the next bit. */
bit = lzms_range_decoder_raw_decode_bit(dec->rd, prob);
- /* Update the state based on the newly decoded bit. */
+ /* Update the state and probability entry based on the decoded bit. */
dec->state = (((dec->state << 1) | bit) & dec->mask);
-
- /* Update the recent bits, including the cached count of 0's. */
- BUILD_BUG_ON(LZMS_PROBABILITY_MAX > sizeof(prob_entry->recent_bits) * 8);
- if (bit == 0) {
- if (prob_entry->recent_bits & (1ULL << (LZMS_PROBABILITY_MAX - 1))) {
- /* Replacing 1 bit with 0 bit; increment the zero count.
- */
- prob_entry->num_recent_zero_bits++;
- }
- } else {
- if (!(prob_entry->recent_bits & (1ULL << (LZMS_PROBABILITY_MAX - 1)))) {
- /* Replacing 0 bit with 1 bit; decrement the zero count.
- */
- prob_entry->num_recent_zero_bits--;
- }
- }
- prob_entry->recent_bits = (prob_entry->recent_bits << 1) | bit;
+ lzms_update_probability_entry(prob_entry, bit);
/* Return the decoded bit. */
return bit;
static u32
lzms_huffman_decode_symbol(struct lzms_huffman_decoder *dec)
{
- const u8 *lens = dec->lens;
const u16 *decode_table = dec->decode_table;
struct lzms_input_bitstream *is = dec->is;
+ u16 entry;
+ u16 key_bits;
+ u16 sym;
/* The Huffman codes used in LZMS are adaptive and must be rebuilt
* whenever a certain number of symbols have been read. Each such
dec->num_syms_read = 0;
}
- /* In the following Huffman decoding implementation, the first
- * LZMS_DECODE_TABLE_BITS of the input are used as an offset into a
- * decode table. The entry will either provide the decoded symbol
- * directly, or else a "real" Huffman binary tree will be searched to
- * decode the symbol. */
-
+ /* XXX: Copied from read_huffsym() (decompress_common.h), since this
+ * uses a different input bitstream type. Should unify the
+ * implementations. */
lzms_input_bitstream_ensure_bits(is, LZMS_MAX_CODEWORD_LEN);
- u16 key_bits = lzms_input_bitstream_peek_bits(is, LZMS_DECODE_TABLE_BITS);
- u16 sym = decode_table[key_bits];
-
- if (sym < dec->num_syms) {
- /* Fast case: The decode table directly provided the symbol. */
- lzms_input_bitstream_remove_bits(is, lens[sym]);
+ /* Index the decode table by the next table_bits bits of the input. */
+ key_bits = lzms_input_bitstream_peek_bits(is, LZMS_DECODE_TABLE_BITS);
+ entry = decode_table[key_bits];
+ if (likely(entry < 0xC000)) {
+ /* Fast case: The decode table directly provided the symbol and
+ * codeword length. The low 11 bits are the symbol, and the
+ * high 5 bits are the codeword length. */
+ lzms_input_bitstream_remove_bits(is, entry >> 11);
+ sym = entry & 0x7FF;
} else {
- /* Slow case: The symbol took too many bits to include directly
- * in the decode table, so search for it in a binary tree at the
- * end of the decode table. */
+ /* Slow case: The codeword for the symbol is longer than
+ * table_bits, so the symbol does not have an entry directly in
+ * the first (1 << table_bits) entries of the decode table.
+ * Traverse the appropriate binary tree bit-by-bit in order to
+ * decode the symbol. */
lzms_input_bitstream_remove_bits(is, LZMS_DECODE_TABLE_BITS);
do {
- key_bits = sym + lzms_input_bitstream_pop_bits(is, 1);
- } while ((sym = decode_table[key_bits]) >= dec->num_syms);
+ key_bits = (entry & 0x3FFF) + lzms_input_bitstream_pop_bits(is, 1);
+ } while ((entry = decode_table[key_bits]) >= 0xC000);
+ sym = entry;
}
/* Tally and return the decoded symbol. */
LZMS_ASSERT(dec->slot_base_tab != NULL);
LZMS_ASSERT(dec->extra_bits_tab != NULL);
- /* Read the slot (position slot, length slot, etc.), which is encoded as
- * a Huffman symbol. */
+ /* Read the slot (offset slot, length slot, etc.), which is encoded as a
+ * Huffman symbol. */
slot = lzms_huffman_decode_symbol(dec);
/* Get the number of extra bits needed to represent the range of values
lzms_copy_lz_match(struct lzms_decompressor *ctx, u32 length, u32 offset)
{
u8 *out_next;
- u8 *matchptr;
if (length > ctx->out_end - ctx->out_next) {
LZMS_DEBUG("Match overrun!");
}
out_next = ctx->out_next;
- matchptr = out_next - offset;
- while (length--)
- *out_next++ = *matchptr++;
- ctx->out_next = out_next;
+ lz_copy(out_next, length, offset, ctx->out_end);
+ ctx->out_next = out_next + length;
+
return 0;
}
return lzms_copy_delta_match(ctx, length, power, raw_offset);
}
-/* Decode a LZ or delta match. */
+/* Decode an LZ or delta match. */
static int
lzms_decode_match(struct lzms_decompressor *ctx)
{
if (ret)
return ret;
- lzms_update_lru_queues(&ctx->lru);
+ lzms_update_lru_queues(&ctx->lru);
return 0;
}
const void *cdata, unsigned clen,
void *ubuf, unsigned ulen)
{
- unsigned num_position_slots;
+ unsigned num_offset_slots;
LZMS_DEBUG("Initializing decompressor (clen=%u, ulen=%u)", clen, ulen);
* backwards) */
lzms_input_bitstream_init(&ctx->is, cdata, clen / 2);
- /* Calculate the number of position slots needed for this compressed
+ /* Calculate the number of offset slots needed for this compressed
* block. */
- num_position_slots = lzms_get_position_slot(ulen - 1) + 1;
+ num_offset_slots = lzms_get_offset_slot(ulen - 1) + 1;
- LZMS_DEBUG("Using %u position slots", num_position_slots);
+ LZMS_DEBUG("Using %u offset slots", num_offset_slots);
/* Initialize Huffman decoders for each alphabet used in the compressed
* representation. */
LZMS_LITERAL_CODE_REBUILD_FREQ);
lzms_init_huffman_decoder(&ctx->lz_offset_decoder, &ctx->is,
- lzms_position_slot_base,
- lzms_extra_position_bits,
- num_position_slots,
+ lzms_offset_slot_base,
+ lzms_extra_offset_bits,
+ num_offset_slots,
LZMS_LZ_OFFSET_CODE_REBUILD_FREQ);
lzms_init_huffman_decoder(&ctx->length_decoder, &ctx->is,
LZMS_LENGTH_CODE_REBUILD_FREQ);
lzms_init_huffman_decoder(&ctx->delta_offset_decoder, &ctx->is,
- lzms_position_slot_base,
- lzms_extra_position_bits,
- num_position_slots,
+ lzms_offset_slot_base,
+ lzms_extra_offset_bits,
+ num_offset_slots,
LZMS_DELTA_OFFSET_CODE_REBUILD_FREQ);
lzms_init_huffman_decoder(&ctx->delta_power_decoder, &ctx->is,
&ctx->rd, LZMS_NUM_DELTA_REPEAT_MATCH_STATES);
/* Initialize LRU match information. */
- lzms_init_lru_queues(&ctx->lru);
+ lzms_init_lru_queues(&ctx->lru);
LZMS_DEBUG("Decompressor successfully initialized");
}
return -1;
}
- /* A LZMS-compressed data block should be evenly divisible into 16-bit
+ /* An LZMS-compressed data block should be evenly divisible into 16-bit
* integers. */
if (compressed_size % 2 != 0) {
LZMS_DEBUG("Compressed size not divisible by 2 (got %zu)",
}
/* Handle the trivial case where nothing needs to be decompressed.
- * (Necessary because a window of size 0 does not have a valid position
+ * (Necessary because a window of size 0 does not have a valid offset
* slot.) */
if (uncompressed_size == 0)
return 0;
- /* The x86 post-processor requires that the uncompressed length fit into
- * a signed 32-bit integer. Also, the position slot table cannot be
- * searched for a position of INT32_MAX or greater. */
- if (uncompressed_size >= INT32_MAX) {
- LZMS_DEBUG("Uncompressed length too large "
- "(got %zu, expected < INT32_MAX)",
- uncompressed_size);
- return -1;
- }
-
/* Decode the literals and matches. */
if (lzms_decode_items(compressed_data, compressed_size,
uncompressed_data, uncompressed_size, ctx))
{
struct lzms_decompressor *ctx = _ctx;
- FREE(ctx);
+ ALIGNED_FREE(ctx);
}
static int
-lzms_create_decompressor(size_t max_block_size,
- const struct wimlib_decompressor_params_header *params,
- void **ctx_ret)
+lzms_create_decompressor(size_t max_block_size, void **ctx_ret)
{
struct lzms_decompressor *ctx;
- ctx = MALLOC(sizeof(struct lzms_decompressor));
+ /* The x86 post-processor requires that the uncompressed length fit into
+ * a signed 32-bit integer. Also, the offset slot table cannot be
+ * searched for an offset of INT32_MAX or greater. */
+ if (max_block_size >= INT32_MAX)
+ return WIMLIB_ERR_INVALID_PARAM;
+
+ ctx = ALIGNED_MALLOC(sizeof(struct lzms_decompressor),
+ DECODE_TABLE_ALIGNMENT);
if (ctx == NULL)
return WIMLIB_ERR_NOMEM;
- /* Initialize position and length slot data if not done already. */
+ /* Initialize offset and length slot data if not done already. */
lzms_init_slots();
*ctx_ret = ctx;
git://wimlib.net / wimlib / blobdiff