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2945 lines
95 KiB
C
2945 lines
95 KiB
C
/*
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* deflate_compress.c - a compressor for DEFLATE
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*
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* Copyright 2016 Eric Biggers
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following
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* conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include "deflate_compress.h"
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#include "deflate_constants.h"
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#include "unaligned.h"
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#include "libdeflate.h"
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/*
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* By default, the near-optimal parsing algorithm is enabled at compression
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* level 10 and above. The near-optimal parsing algorithm produces a
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* compression ratio significantly better than the greedy and lazy algorithms
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* implemented here, and also the algorithm used by zlib at level 9. However,
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* it is slow.
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*/
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#define SUPPORT_NEAR_OPTIMAL_PARSING 1
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/*
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* Define to 1 to maintain the full map from match offsets to offset slots.
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* This slightly speeds up translations of match offsets to offset slots, but it
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* uses 32769 bytes of memory rather than the 512 bytes used by the condensed
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* map. The speedup provided by the larger map is most helpful when the
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* near-optimal parsing algorithm is being used.
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*/
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#define USE_FULL_OFFSET_SLOT_FAST SUPPORT_NEAR_OPTIMAL_PARSING
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/* Include the needed matchfinders. */
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#define MATCHFINDER_WINDOW_ORDER DEFLATE_WINDOW_ORDER
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#include "hc_matchfinder.h"
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#if SUPPORT_NEAR_OPTIMAL_PARSING
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# include "bt_matchfinder.h"
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#endif
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/*
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* The compressor always chooses a block of at least MIN_BLOCK_LENGTH bytes,
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* except if the last block has to be shorter.
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*/
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#define MIN_BLOCK_LENGTH 10000
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/*
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* The compressor attempts to end blocks after SOFT_MAX_BLOCK_LENGTH bytes, but
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* the final length might be slightly longer due to matches extending beyond
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* this limit.
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*/
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#define SOFT_MAX_BLOCK_LENGTH 300000
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/*
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* The number of observed matches or literals that represents sufficient data to
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* decide whether the current block should be terminated or not.
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*/
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#define NUM_OBSERVATIONS_PER_BLOCK_CHECK 512
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#if SUPPORT_NEAR_OPTIMAL_PARSING
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/* Constants specific to the near-optimal parsing algorithm */
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/*
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* The maximum number of matches the matchfinder can find at a single position.
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* Since the matchfinder never finds more than one match for the same length,
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* presuming one of each possible length is sufficient for an upper bound.
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* (This says nothing about whether it is worthwhile to consider so many
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* matches; this is just defining the worst case.)
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*/
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# define MAX_MATCHES_PER_POS (DEFLATE_MAX_MATCH_LEN - DEFLATE_MIN_MATCH_LEN + 1)
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/*
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* The number of lz_match structures in the match cache, excluding the extra
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* "overflow" entries. This value should be high enough so that nearly the
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* time, all matches found in a given block can fit in the match cache.
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* However, fallback behavior (immediately terminating the block) on cache
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* overflow is still required.
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*/
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# define CACHE_LENGTH (SOFT_MAX_BLOCK_LENGTH * 5)
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#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
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/*
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* These are the compressor-side limits on the codeword lengths for each Huffman
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* code. To make outputting bits slightly faster, some of these limits are
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* lower than the limits defined by the DEFLATE format. This does not
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* significantly affect the compression ratio, at least for the block lengths we
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* use.
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*/
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#define MAX_LITLEN_CODEWORD_LEN 14
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#define MAX_OFFSET_CODEWORD_LEN DEFLATE_MAX_OFFSET_CODEWORD_LEN
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#define MAX_PRE_CODEWORD_LEN DEFLATE_MAX_PRE_CODEWORD_LEN
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/* Table: length slot => length slot base value */
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static const unsigned deflate_length_slot_base[] = {
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3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ,
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11 , 13 , 15 , 17 , 19 , 23 , 27 , 31 ,
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35 , 43 , 51 , 59 , 67 , 83 , 99 , 115 ,
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131 , 163 , 195 , 227 , 258 ,
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};
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/* Table: length slot => number of extra length bits */
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static const u8 deflate_extra_length_bits[] = {
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0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ,
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1 , 1 , 1 , 1 , 2 , 2 , 2 , 2 ,
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3 , 3 , 3 , 3 , 4 , 4 , 4 , 4 ,
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5 , 5 , 5 , 5 , 0 ,
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};
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/* Table: offset slot => offset slot base value */
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static const unsigned deflate_offset_slot_base[] = {
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1 , 2 , 3 , 4 , 5 , 7 , 9 , 13 ,
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17 , 25 , 33 , 49 , 65 , 97 , 129 , 193 ,
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257 , 385 , 513 , 769 , 1025 , 1537 , 2049 , 3073 ,
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4097 , 6145 , 8193 , 12289 , 16385 , 24577 ,
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};
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/* Table: offset slot => number of extra offset bits */
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static const u8 deflate_extra_offset_bits[] = {
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0 , 0 , 0 , 0 , 1 , 1 , 2 , 2 ,
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3 , 3 , 4 , 4 , 5 , 5 , 6 , 6 ,
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7 , 7 , 8 , 8 , 9 , 9 , 10 , 10 ,
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11 , 11 , 12 , 12 , 13 , 13 ,
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};
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/* Table: length => length slot */
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static const u8 deflate_length_slot[DEFLATE_MAX_MATCH_LEN + 1] = {
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0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 12,
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12, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 16,
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16, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18,
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18, 19, 19, 19, 19, 19, 19, 19, 19, 20, 20, 20, 20, 20, 20, 20, 20, 20,
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20, 20, 20, 20, 20, 20, 20, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
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21, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
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22, 22, 22, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
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23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
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24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 25, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
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25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
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26, 26, 26, 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
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27, 27, 28,
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};
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/* The order in which precode codeword lengths are stored */
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static const u8 deflate_precode_lens_permutation[DEFLATE_NUM_PRECODE_SYMS] = {
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16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
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};
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/* Codewords for the DEFLATE Huffman codes. */
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struct deflate_codewords {
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u32 litlen[DEFLATE_NUM_LITLEN_SYMS];
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u32 offset[DEFLATE_NUM_OFFSET_SYMS];
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};
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/* Codeword lengths (in bits) for the DEFLATE Huffman codes.
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* A zero length means the corresponding symbol had zero frequency. */
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struct deflate_lens {
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u8 litlen[DEFLATE_NUM_LITLEN_SYMS];
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u8 offset[DEFLATE_NUM_OFFSET_SYMS];
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};
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/* Codewords and lengths for the DEFLATE Huffman codes. */
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struct deflate_codes {
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struct deflate_codewords codewords;
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struct deflate_lens lens;
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};
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/* Symbol frequency counters for the DEFLATE Huffman codes. */
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struct deflate_freqs {
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u32 litlen[DEFLATE_NUM_LITLEN_SYMS];
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u32 offset[DEFLATE_NUM_OFFSET_SYMS];
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};
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#if SUPPORT_NEAR_OPTIMAL_PARSING
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/* Costs for the near-optimal parsing algorithm. */
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struct deflate_costs {
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/* The cost to output each possible literal. */
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u32 literal[DEFLATE_NUM_LITERALS];
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/* The cost to output each possible match length. */
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u32 length[DEFLATE_MAX_MATCH_LEN + 1];
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/* The cost to output a match offset of each possible offset slot. */
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u32 offset_slot[DEFLATE_NUM_OFFSET_SYMS];
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};
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/*
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* BIT_COST is a scaling factor that allows the compressor to consider
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* fractional bit costs when deciding which literal/match sequence to use. This
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* is useful when the true symbol costs are unknown. For example, if the
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* compressor thinks that a symbol has 6.5 bits of entropy, it can set its cost
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* to 6.5 bits rather than have to use 6 or 7 bits. Although in the end each
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* symbol will use a whole number of bits due to the Huffman coding, considering
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* fractional bits can be helpful due to the limited information.
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*
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* BIT_COST should be a power of 2. A value of 8 or 16 works well. A higher
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* value isn't very useful since the calculations are approximate anyway.
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*/
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#define BIT_COST 8
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/*
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* The NOSTAT_BITS value for a given alphabet is the number of bits assumed to
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* be needed to output a symbol that was unused in the previous optimization
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* pass. Assigning a default cost allows the symbol to be used in the next
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* optimization pass. However, the cost should be relatively high because the
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* symbol probably won't be used very many times (if at all).
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*/
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#define LITERAL_NOSTAT_BITS 13
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#define LENGTH_NOSTAT_BITS 13
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#define OFFSET_NOSTAT_BITS 10
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#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
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/*
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* Represents a run of literals followed by a match or end-of-block. This
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* struct is needed to temporarily store items chosen by the parser, since items
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* cannot be written until all items for the block have been chosen and the
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* block's Huffman codes have been computed.
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*/
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struct deflate_sequence {
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/* Bits 0..22: the number of literals in this run. This may be 0 and
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* can be at most about SOFT_MAX_BLOCK_LENGTH. The literals are not
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* stored explicitly in this structure; instead, they are read directly
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* from the uncompressed data.
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*
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* Bits 23..31: the length of the match which follows the literals, or 0
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* if this literal run was the last in the block, so there is no match
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* which follows it. */
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u32 litrunlen_and_length;
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/* If 'length' doesn't indicate end-of-block, then this is the offset of
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* the match which follows the literals. */
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u16 offset;
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/* If 'length' doesn't indicate end-of-block, then this is the offset
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* symbol of the match which follows the literals. */
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u8 offset_symbol;
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/* If 'length' doesn't indicate end-of-block, then this is the length
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* slot of the match which follows the literals. */
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u8 length_slot;
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};
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#if SUPPORT_NEAR_OPTIMAL_PARSING
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/*
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* This structure represents a byte position in the input data and a node in the
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* graph of possible match/literal choices for the current block.
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*
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* Logically, each incoming edge to this node is labeled with a literal or a
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* match that can be taken to reach this position from an earlier position; and
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* each outgoing edge from this node is labeled with a literal or a match that
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* can be taken to advance from this position to a later position.
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*
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* But these "edges" are actually stored elsewhere (in 'match_cache'). Here we
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* associate with each node just two pieces of information:
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*
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* 'cost_to_end' is the minimum cost to reach the end of the block from
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* this position.
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*
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* 'item' represents the literal or match that must be chosen from here to
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* reach the end of the block with the minimum cost. Equivalently, this
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* can be interpreted as the label of the outgoing edge on the minimum-cost
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* path to the "end of block" node from this node.
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*/
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struct deflate_optimum_node {
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u32 cost_to_end;
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/*
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* Notes on the match/literal representation used here:
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*
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* The low bits of 'item' are the length: 1 if this is a literal,
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* or the match length if this is a match.
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*
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* The high bits of 'item' are the actual literal byte if this is a
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* literal, or the match offset if this is a match.
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*/
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#define OPTIMUM_OFFSET_SHIFT 9
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#define OPTIMUM_LEN_MASK (((u32)1 << OPTIMUM_OFFSET_SHIFT) - 1)
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u32 item;
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};
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#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
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/* Block split statistics. See "Block splitting algorithm" below. */
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#define NUM_LITERAL_OBSERVATION_TYPES 8
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#define NUM_MATCH_OBSERVATION_TYPES 2
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#define NUM_OBSERVATION_TYPES (NUM_LITERAL_OBSERVATION_TYPES + NUM_MATCH_OBSERVATION_TYPES)
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struct block_split_stats {
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u32 new_observations[NUM_OBSERVATION_TYPES];
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u32 observations[NUM_OBSERVATION_TYPES];
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u32 num_new_observations;
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u32 num_observations;
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};
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/* The main DEFLATE compressor structure */
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struct libdeflate_compressor {
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/* Pointer to the compress() implementation chosen at allocation time */
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size_t (*impl)(struct libdeflate_compressor *,
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const u8 *, size_t, u8 *, size_t);
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/* Frequency counters for the current block */
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struct deflate_freqs freqs;
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/* Dynamic Huffman codes for the current block */
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struct deflate_codes codes;
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/* Static Huffman codes */
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struct deflate_codes static_codes;
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/* Block split statistics for the currently pending block */
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struct block_split_stats split_stats;
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/* A table for fast lookups of offset slot by match offset.
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*
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* If the full table is being used, it is a direct mapping from offset
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* to offset slot.
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*
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* If the condensed table is being used, the first 256 entries map
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* directly to the offset slots of offsets 1 through 256. The next 256
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* entries map to the offset slots for the remaining offsets, stepping
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* through the offsets with a stride of 128. This relies on the fact
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* that each of the remaining offset slots contains at least 128 offsets
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* and has an offset base that is a multiple of 128. */
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#if USE_FULL_OFFSET_SLOT_FAST
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u8 offset_slot_fast[DEFLATE_MAX_MATCH_OFFSET + 1];
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#else
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u8 offset_slot_fast[512];
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#endif
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/* The "nice" match length: if a match of this length is found, choose
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* it immediately without further consideration. */
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unsigned nice_match_length;
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/* The maximum search depth: consider at most this many potential
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* matches at each position. */
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unsigned max_search_depth;
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/* The compression level with which this compressor was created. */
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unsigned compression_level;
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/* Anything smaller than this we won't bother trying to compress. */
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unsigned min_size_to_compress;
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/* Temporary space for Huffman code output */
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u32 precode_freqs[DEFLATE_NUM_PRECODE_SYMS];
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u8 precode_lens[DEFLATE_NUM_PRECODE_SYMS];
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u32 precode_codewords[DEFLATE_NUM_PRECODE_SYMS];
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unsigned precode_items[DEFLATE_NUM_LITLEN_SYMS + DEFLATE_NUM_OFFSET_SYMS];
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unsigned num_litlen_syms;
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unsigned num_offset_syms;
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unsigned num_explicit_lens;
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unsigned num_precode_items;
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union {
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/* Data for greedy or lazy parsing */
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struct {
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/* Hash chain matchfinder */
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struct hc_matchfinder hc_mf;
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/* The matches and literals that the parser has chosen
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* for the current block. The required length of this
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* array is limited by the maximum number of matches
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* that can ever be chosen for a single block, plus one
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* for the special entry at the end. */
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struct deflate_sequence sequences[
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DIV_ROUND_UP(SOFT_MAX_BLOCK_LENGTH,
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DEFLATE_MIN_MATCH_LEN) + 1];
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} g; /* (g)reedy */
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#if SUPPORT_NEAR_OPTIMAL_PARSING
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/* Data for near-optimal parsing */
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struct {
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/* Binary tree matchfinder */
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struct bt_matchfinder bt_mf;
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/*
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* Cached matches for the current block. This array
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* contains the matches that were found at each position
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* in the block. Specifically, for each position, there
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* is a list of matches found at that position, if any,
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* sorted by strictly increasing length. In addition,
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* following the matches for each position, there is a
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* special 'struct lz_match' whose 'length' member
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* contains the number of matches found at that
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* position, and whose 'offset' member contains the
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* literal at that position.
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*
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* Note: in rare cases, there will be a very high number
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* of matches in the block and this array will overflow.
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* If this happens, we force the end of the current
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* block. CACHE_LENGTH is the length at which we
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* actually check for overflow. The extra slots beyond
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* this are enough to absorb the worst case overflow,
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* which occurs if starting at &match_cache[CACHE_LENGTH
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* - 1], we write MAX_MATCHES_PER_POS matches and a
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* match count header, then skip searching for matches
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* at 'DEFLATE_MAX_MATCH_LEN - 1' positions and write
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* the match count header for each.
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*/
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struct lz_match match_cache[CACHE_LENGTH +
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MAX_MATCHES_PER_POS +
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DEFLATE_MAX_MATCH_LEN - 1];
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/*
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* Array of nodes, one per position, for running the
|
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* minimum-cost path algorithm.
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*
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* This array must be large enough to accommodate the
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* worst-case number of nodes, which occurs if we find a
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* match of length DEFLATE_MAX_MATCH_LEN at position
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* SOFT_MAX_BLOCK_LENGTH - 1, producing a block of
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* length SOFT_MAX_BLOCK_LENGTH - 1 +
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* DEFLATE_MAX_MATCH_LEN. Add one for the end-of-block
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* node.
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*/
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struct deflate_optimum_node optimum_nodes[SOFT_MAX_BLOCK_LENGTH - 1 +
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DEFLATE_MAX_MATCH_LEN + 1];
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/* The current cost model being used. */
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struct deflate_costs costs;
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unsigned num_optim_passes;
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} n; /* (n)ear-optimal */
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#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
|
|
|
|
} p; /* (p)arser */
|
|
};
|
|
|
|
/*
|
|
* The type for the bitbuffer variable, which temporarily holds bits that are
|
|
* being packed into bytes and written to the output buffer. For best
|
|
* performance, this should have size equal to a machine word.
|
|
*/
|
|
typedef machine_word_t bitbuf_t;
|
|
#define BITBUF_NBITS (8 * sizeof(bitbuf_t))
|
|
|
|
/* Can the specified number of bits always be added to 'bitbuf' after any
|
|
* pending bytes have been flushed? */
|
|
#define CAN_BUFFER(n) ((n) <= BITBUF_NBITS - 7)
|
|
|
|
/*
|
|
* Structure to keep track of the current state of sending bits to the
|
|
* compressed output buffer.
|
|
*/
|
|
struct deflate_output_bitstream {
|
|
|
|
/* Bits that haven't yet been written to the output buffer. */
|
|
bitbuf_t bitbuf;
|
|
|
|
/* Number of bits currently held in @bitbuf. */
|
|
unsigned bitcount;
|
|
|
|
/* Pointer to the beginning of the output buffer. */
|
|
u8 *begin;
|
|
|
|
/* Pointer to the position in the output buffer at which the next byte
|
|
* should be written. */
|
|
u8 *next;
|
|
|
|
/* Pointer just past the end of the output buffer. */
|
|
u8 *end;
|
|
};
|
|
|
|
/*
|
|
* OUTPUT_END_PADDING is the size, in bytes, of the extra space that must be
|
|
* present following os->end, in order to not overrun the buffer when generating
|
|
* output. When UNALIGNED_ACCESS_IS_FAST, we need at least sizeof(bitbuf_t)
|
|
* bytes for put_unaligned_leword(). Otherwise we need only 1 byte. However,
|
|
* to make the compression algorithm produce the same result on all CPU
|
|
* architectures (which is sometimes desirable), we have to unconditionally use
|
|
* the maximum for any CPU, which is sizeof(bitbuf_t) == 8.
|
|
*/
|
|
#define OUTPUT_END_PADDING 8
|
|
|
|
/* Initialize the output bitstream. 'size' is assumed to be at least
|
|
* OUTPUT_END_PADDING. */
|
|
static void
|
|
deflate_init_output(struct deflate_output_bitstream *os,
|
|
void *buffer, size_t size)
|
|
{
|
|
os->bitbuf = 0;
|
|
os->bitcount = 0;
|
|
os->begin = buffer;
|
|
os->next = os->begin;
|
|
os->end = os->begin + size - OUTPUT_END_PADDING;
|
|
}
|
|
|
|
/* Add some bits to the bitbuffer variable of the output bitstream. The caller
|
|
* must make sure there is enough room. */
|
|
static forceinline void
|
|
deflate_add_bits(struct deflate_output_bitstream *os,
|
|
const bitbuf_t bits, const unsigned num_bits)
|
|
{
|
|
os->bitbuf |= bits << os->bitcount;
|
|
os->bitcount += num_bits;
|
|
}
|
|
|
|
/* Flush bits from the bitbuffer variable to the output buffer. */
|
|
static forceinline void
|
|
deflate_flush_bits(struct deflate_output_bitstream *os)
|
|
{
|
|
if (UNALIGNED_ACCESS_IS_FAST) {
|
|
/* Flush a whole word (branchlessly). */
|
|
put_unaligned_leword(os->bitbuf, os->next);
|
|
os->bitbuf >>= os->bitcount & ~7;
|
|
os->next += MIN(os->end - os->next, os->bitcount >> 3);
|
|
os->bitcount &= 7;
|
|
} else {
|
|
/* Flush a byte at a time. */
|
|
while (os->bitcount >= 8) {
|
|
*os->next = os->bitbuf;
|
|
if (os->next != os->end)
|
|
os->next++;
|
|
os->bitcount -= 8;
|
|
os->bitbuf >>= 8;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Align the bitstream on a byte boundary. */
|
|
static forceinline void
|
|
deflate_align_bitstream(struct deflate_output_bitstream *os)
|
|
{
|
|
os->bitcount += -os->bitcount & 7;
|
|
deflate_flush_bits(os);
|
|
}
|
|
|
|
/*
|
|
* Flush any remaining bits to the output buffer if needed. Return the total
|
|
* number of bytes written to the output buffer, or 0 if an overflow occurred.
|
|
*/
|
|
static size_t
|
|
deflate_flush_output(struct deflate_output_bitstream *os)
|
|
{
|
|
if (os->next == os->end) /* overflow? */
|
|
return 0;
|
|
|
|
while ((int)os->bitcount > 0) {
|
|
*os->next++ = os->bitbuf;
|
|
os->bitcount -= 8;
|
|
os->bitbuf >>= 8;
|
|
}
|
|
|
|
return os->next - os->begin;
|
|
}
|
|
|
|
/* Given the binary tree node A[subtree_idx] whose children already
|
|
* satisfy the maxheap property, swap the node with its greater child
|
|
* until it is greater than both its children, so that the maxheap
|
|
* property is satisfied in the subtree rooted at A[subtree_idx]. */
|
|
static void
|
|
heapify_subtree(u32 A[], unsigned length, unsigned subtree_idx)
|
|
{
|
|
unsigned parent_idx;
|
|
unsigned child_idx;
|
|
u32 v;
|
|
|
|
v = A[subtree_idx];
|
|
parent_idx = subtree_idx;
|
|
while ((child_idx = parent_idx * 2) <= length) {
|
|
if (child_idx < length && A[child_idx + 1] > A[child_idx])
|
|
child_idx++;
|
|
if (v >= A[child_idx])
|
|
break;
|
|
A[parent_idx] = A[child_idx];
|
|
parent_idx = child_idx;
|
|
}
|
|
A[parent_idx] = v;
|
|
}
|
|
|
|
/* Rearrange the array 'A' so that it satisfies the maxheap property.
|
|
* 'A' uses 1-based indices, so the children of A[i] are A[i*2] and A[i*2 + 1].
|
|
*/
|
|
static void
|
|
heapify_array(u32 A[], unsigned length)
|
|
{
|
|
unsigned subtree_idx;
|
|
|
|
for (subtree_idx = length / 2; subtree_idx >= 1; subtree_idx--)
|
|
heapify_subtree(A, length, subtree_idx);
|
|
}
|
|
|
|
/*
|
|
* Sort the array 'A', which contains 'length' unsigned 32-bit integers.
|
|
*
|
|
* Note: name this function heap_sort() instead of heapsort() to avoid colliding
|
|
* with heapsort() from stdlib.h on BSD-derived systems --- though this isn't
|
|
* necessary when compiling with -D_ANSI_SOURCE, which is the better solution.
|
|
*/
|
|
static void
|
|
heap_sort(u32 A[], unsigned length)
|
|
{
|
|
A--; /* Use 1-based indices */
|
|
|
|
heapify_array(A, length);
|
|
|
|
while (length >= 2) {
|
|
u32 tmp = A[length];
|
|
A[length] = A[1];
|
|
A[1] = tmp;
|
|
length--;
|
|
heapify_subtree(A, length, 1);
|
|
}
|
|
}
|
|
|
|
#define NUM_SYMBOL_BITS 10
|
|
#define SYMBOL_MASK ((1 << NUM_SYMBOL_BITS) - 1)
|
|
|
|
#define GET_NUM_COUNTERS(num_syms) ((((num_syms) + 3 / 4) + 3) & ~3)
|
|
/*
|
|
* Sort the symbols primarily by frequency and secondarily by symbol
|
|
* value. Discard symbols with zero frequency and fill in an array with
|
|
* the remaining symbols, along with their frequencies. The low
|
|
* NUM_SYMBOL_BITS bits of each array entry will contain the symbol
|
|
* value, and the remaining bits will contain the frequency.
|
|
*
|
|
* @num_syms
|
|
* Number of symbols in the alphabet.
|
|
* Can't be greater than (1 << NUM_SYMBOL_BITS).
|
|
*
|
|
* @freqs[num_syms]
|
|
* The frequency of each symbol.
|
|
*
|
|
* @lens[num_syms]
|
|
* An array that eventually will hold the length of each codeword.
|
|
* This function only fills in the codeword lengths for symbols that
|
|
* have zero frequency, which are not well defined per se but will
|
|
* be set to 0.
|
|
*
|
|
* @symout[num_syms]
|
|
* The output array, described above.
|
|
*
|
|
* Returns the number of entries in 'symout' that were filled. This is
|
|
* the number of symbols that have nonzero frequency.
|
|
*/
|
|
static unsigned
|
|
sort_symbols(unsigned num_syms, const u32 freqs[restrict],
|
|
u8 lens[restrict], u32 symout[restrict])
|
|
{
|
|
unsigned sym;
|
|
unsigned i;
|
|
unsigned num_used_syms;
|
|
unsigned num_counters;
|
|
unsigned counters[GET_NUM_COUNTERS(DEFLATE_MAX_NUM_SYMS)];
|
|
|
|
/* We rely on heapsort, but with an added optimization. Since
|
|
* it's common for most symbol frequencies to be low, we first do
|
|
* a count sort using a limited number of counters. High
|
|
* frequencies will be counted in the last counter, and only they
|
|
* will be sorted with heapsort.
|
|
*
|
|
* Note: with more symbols, it is generally beneficial to have more
|
|
* counters. About 1 counter per 4 symbols seems fast.
|
|
*
|
|
* Note: I also tested radix sort, but even for large symbol
|
|
* counts (> 255) and frequencies bounded at 16 bits (enabling
|
|
* radix sort by just two base-256 digits), it didn't seem any
|
|
* faster than the method implemented here.
|
|
*
|
|
* Note: I tested the optimized quicksort implementation from
|
|
* glibc (with indirection overhead removed), but it was only
|
|
* marginally faster than the simple heapsort implemented here.
|
|
*
|
|
* Tests were done with building the codes for LZX. Results may
|
|
* vary for different compression algorithms...! */
|
|
|
|
num_counters = GET_NUM_COUNTERS(num_syms);
|
|
|
|
memset(counters, 0, num_counters * sizeof(counters[0]));
|
|
|
|
/* Count the frequencies. */
|
|
for (sym = 0; sym < num_syms; sym++)
|
|
counters[MIN(freqs[sym], num_counters - 1)]++;
|
|
|
|
/* Make the counters cumulative, ignoring the zero-th, which
|
|
* counted symbols with zero frequency. As a side effect, this
|
|
* calculates the number of symbols with nonzero frequency. */
|
|
num_used_syms = 0;
|
|
for (i = 1; i < num_counters; i++) {
|
|
unsigned count = counters[i];
|
|
counters[i] = num_used_syms;
|
|
num_used_syms += count;
|
|
}
|
|
|
|
/* Sort nonzero-frequency symbols using the counters. At the
|
|
* same time, set the codeword lengths of zero-frequency symbols
|
|
* to 0. */
|
|
for (sym = 0; sym < num_syms; sym++) {
|
|
u32 freq = freqs[sym];
|
|
if (freq != 0) {
|
|
symout[counters[MIN(freq, num_counters - 1)]++] =
|
|
sym | (freq << NUM_SYMBOL_BITS);
|
|
} else {
|
|
lens[sym] = 0;
|
|
}
|
|
}
|
|
|
|
/* Sort the symbols counted in the last counter. */
|
|
heap_sort(symout + counters[num_counters - 2],
|
|
counters[num_counters - 1] - counters[num_counters - 2]);
|
|
|
|
return num_used_syms;
|
|
}
|
|
|
|
/*
|
|
* Build the Huffman tree.
|
|
*
|
|
* This is an optimized implementation that
|
|
* (a) takes advantage of the frequencies being already sorted;
|
|
* (b) only generates non-leaf nodes, since the non-leaf nodes of a
|
|
* Huffman tree are sufficient to generate a canonical code;
|
|
* (c) Only stores parent pointers, not child pointers;
|
|
* (d) Produces the nodes in the same memory used for input
|
|
* frequency information.
|
|
*
|
|
* Array 'A', which contains 'sym_count' entries, is used for both input
|
|
* and output. For this function, 'sym_count' must be at least 2.
|
|
*
|
|
* For input, the array must contain the frequencies of the symbols,
|
|
* sorted in increasing order. Specifically, each entry must contain a
|
|
* frequency left shifted by NUM_SYMBOL_BITS bits. Any data in the low
|
|
* NUM_SYMBOL_BITS bits of the entries will be ignored by this function.
|
|
* Although these bits will, in fact, contain the symbols that correspond
|
|
* to the frequencies, this function is concerned with frequencies only
|
|
* and keeps the symbols as-is.
|
|
*
|
|
* For output, this function will produce the non-leaf nodes of the
|
|
* Huffman tree. These nodes will be stored in the first (sym_count - 1)
|
|
* entries of the array. Entry A[sym_count - 2] will represent the root
|
|
* node. Each other node will contain the zero-based index of its parent
|
|
* node in 'A', left shifted by NUM_SYMBOL_BITS bits. The low
|
|
* NUM_SYMBOL_BITS bits of each entry in A will be kept as-is. Again,
|
|
* note that although these low bits will, in fact, contain a symbol
|
|
* value, this symbol will have *no relationship* with the Huffman tree
|
|
* node that happens to occupy the same slot. This is because this
|
|
* implementation only generates the non-leaf nodes of the tree.
|
|
*/
|
|
static void
|
|
build_tree(u32 A[], unsigned sym_count)
|
|
{
|
|
/* Index, in 'A', of next lowest frequency symbol that has not
|
|
* yet been processed. */
|
|
unsigned i = 0;
|
|
|
|
/* Index, in 'A', of next lowest frequency parentless non-leaf
|
|
* node; or, if equal to 'e', then no such node exists yet. */
|
|
unsigned b = 0;
|
|
|
|
/* Index, in 'A', of next node to allocate as a non-leaf. */
|
|
unsigned e = 0;
|
|
|
|
do {
|
|
unsigned m, n;
|
|
u32 freq_shifted;
|
|
|
|
/* Choose the two next lowest frequency entries. */
|
|
|
|
if (i != sym_count &&
|
|
(b == e || (A[i] >> NUM_SYMBOL_BITS) <= (A[b] >> NUM_SYMBOL_BITS)))
|
|
m = i++;
|
|
else
|
|
m = b++;
|
|
|
|
if (i != sym_count &&
|
|
(b == e || (A[i] >> NUM_SYMBOL_BITS) <= (A[b] >> NUM_SYMBOL_BITS)))
|
|
n = i++;
|
|
else
|
|
n = b++;
|
|
|
|
/* Allocate a non-leaf node and link the entries to it.
|
|
*
|
|
* If we link an entry that we're visiting for the first
|
|
* time (via index 'i'), then we're actually linking a
|
|
* leaf node and it will have no effect, since the leaf
|
|
* will be overwritten with a non-leaf when index 'e'
|
|
* catches up to it. But it's not any slower to
|
|
* unconditionally set the parent index.
|
|
*
|
|
* We also compute the frequency of the non-leaf node as
|
|
* the sum of its two children's frequencies. */
|
|
|
|
freq_shifted = (A[m] & ~SYMBOL_MASK) + (A[n] & ~SYMBOL_MASK);
|
|
|
|
A[m] = (A[m] & SYMBOL_MASK) | (e << NUM_SYMBOL_BITS);
|
|
A[n] = (A[n] & SYMBOL_MASK) | (e << NUM_SYMBOL_BITS);
|
|
A[e] = (A[e] & SYMBOL_MASK) | freq_shifted;
|
|
e++;
|
|
} while (sym_count - e > 1);
|
|
/* When just one entry remains, it is a "leaf" that was
|
|
* linked to some other node. We ignore it, since the
|
|
* rest of the array contains the non-leaves which we
|
|
* need. (Note that we're assuming the cases with 0 or 1
|
|
* symbols were handled separately.) */
|
|
}
|
|
|
|
/*
|
|
* Given the stripped-down Huffman tree constructed by build_tree(),
|
|
* determine the number of codewords that should be assigned each
|
|
* possible length, taking into account the length-limited constraint.
|
|
*
|
|
* @A
|
|
* The array produced by build_tree(), containing parent index
|
|
* information for the non-leaf nodes of the Huffman tree. Each
|
|
* entry in this array is a node; a node's parent always has a
|
|
* greater index than that node itself. This function will
|
|
* overwrite the parent index information in this array, so
|
|
* essentially it will destroy the tree. However, the data in the
|
|
* low NUM_SYMBOL_BITS of each entry will be preserved.
|
|
*
|
|
* @root_idx
|
|
* The 0-based index of the root node in 'A', and consequently one
|
|
* less than the number of tree node entries in 'A'. (Or, really 2
|
|
* less than the actual length of 'A'.)
|
|
*
|
|
* @len_counts
|
|
* An array of length ('max_codeword_len' + 1) in which the number of
|
|
* codewords having each length <= max_codeword_len will be
|
|
* returned.
|
|
*
|
|
* @max_codeword_len
|
|
* The maximum permissible codeword length.
|
|
*/
|
|
static void
|
|
compute_length_counts(u32 A[restrict], unsigned root_idx,
|
|
unsigned len_counts[restrict], unsigned max_codeword_len)
|
|
{
|
|
unsigned len;
|
|
int node;
|
|
|
|
/* The key observations are:
|
|
*
|
|
* (1) We can traverse the non-leaf nodes of the tree, always
|
|
* visiting a parent before its children, by simply iterating
|
|
* through the array in reverse order. Consequently, we can
|
|
* compute the depth of each node in one pass, overwriting the
|
|
* parent indices with depths.
|
|
*
|
|
* (2) We can initially assume that in the real Huffman tree,
|
|
* both children of the root are leaves. This corresponds to two
|
|
* codewords of length 1. Then, whenever we visit a (non-leaf)
|
|
* node during the traversal, we modify this assumption to
|
|
* account for the current node *not* being a leaf, but rather
|
|
* its two children being leaves. This causes the loss of one
|
|
* codeword for the current depth and the addition of two
|
|
* codewords for the current depth plus one.
|
|
*
|
|
* (3) We can handle the length-limited constraint fairly easily
|
|
* by simply using the largest length available when a depth
|
|
* exceeds max_codeword_len.
|
|
*/
|
|
|
|
for (len = 0; len <= max_codeword_len; len++)
|
|
len_counts[len] = 0;
|
|
len_counts[1] = 2;
|
|
|
|
/* Set the root node's depth to 0. */
|
|
A[root_idx] &= SYMBOL_MASK;
|
|
|
|
for (node = root_idx - 1; node >= 0; node--) {
|
|
|
|
/* Calculate the depth of this node. */
|
|
|
|
unsigned parent = A[node] >> NUM_SYMBOL_BITS;
|
|
unsigned parent_depth = A[parent] >> NUM_SYMBOL_BITS;
|
|
unsigned depth = parent_depth + 1;
|
|
unsigned len = depth;
|
|
|
|
/* Set the depth of this node so that it is available
|
|
* when its children (if any) are processed. */
|
|
|
|
A[node] = (A[node] & SYMBOL_MASK) | (depth << NUM_SYMBOL_BITS);
|
|
|
|
/* If needed, decrease the length to meet the
|
|
* length-limited constraint. This is not the optimal
|
|
* method for generating length-limited Huffman codes!
|
|
* But it should be good enough. */
|
|
if (len >= max_codeword_len) {
|
|
len = max_codeword_len;
|
|
do {
|
|
len--;
|
|
} while (len_counts[len] == 0);
|
|
}
|
|
|
|
/* Account for the fact that we have a non-leaf node at
|
|
* the current depth. */
|
|
len_counts[len]--;
|
|
len_counts[len + 1] += 2;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Generate the codewords for a canonical Huffman code.
|
|
*
|
|
* @A
|
|
* The output array for codewords. In addition, initially this
|
|
* array must contain the symbols, sorted primarily by frequency and
|
|
* secondarily by symbol value, in the low NUM_SYMBOL_BITS bits of
|
|
* each entry.
|
|
*
|
|
* @len
|
|
* Output array for codeword lengths.
|
|
*
|
|
* @len_counts
|
|
* An array that provides the number of codewords that will have
|
|
* each possible length <= max_codeword_len.
|
|
*
|
|
* @max_codeword_len
|
|
* Maximum length, in bits, of each codeword.
|
|
*
|
|
* @num_syms
|
|
* Number of symbols in the alphabet, including symbols with zero
|
|
* frequency. This is the length of the 'A' and 'len' arrays.
|
|
*/
|
|
static void
|
|
gen_codewords(u32 A[restrict], u8 lens[restrict],
|
|
const unsigned len_counts[restrict],
|
|
unsigned max_codeword_len, unsigned num_syms)
|
|
{
|
|
u32 next_codewords[DEFLATE_MAX_CODEWORD_LEN + 1];
|
|
unsigned i;
|
|
unsigned len;
|
|
unsigned sym;
|
|
|
|
/* Given the number of codewords that will have each length,
|
|
* assign codeword lengths to symbols. We do this by assigning
|
|
* the lengths in decreasing order to the symbols sorted
|
|
* primarily by increasing frequency and secondarily by
|
|
* increasing symbol value. */
|
|
for (i = 0, len = max_codeword_len; len >= 1; len--) {
|
|
unsigned count = len_counts[len];
|
|
while (count--)
|
|
lens[A[i++] & SYMBOL_MASK] = len;
|
|
}
|
|
|
|
/* Generate the codewords themselves. We initialize the
|
|
* 'next_codewords' array to provide the lexicographically first
|
|
* codeword of each length, then assign codewords in symbol
|
|
* order. This produces a canonical code. */
|
|
next_codewords[0] = 0;
|
|
next_codewords[1] = 0;
|
|
for (len = 2; len <= max_codeword_len; len++)
|
|
next_codewords[len] =
|
|
(next_codewords[len - 1] + len_counts[len - 1]) << 1;
|
|
|
|
for (sym = 0; sym < num_syms; sym++)
|
|
A[sym] = next_codewords[lens[sym]]++;
|
|
}
|
|
|
|
/*
|
|
* ---------------------------------------------------------------------
|
|
* make_canonical_huffman_code()
|
|
* ---------------------------------------------------------------------
|
|
*
|
|
* Given an alphabet and the frequency of each symbol in it, construct a
|
|
* length-limited canonical Huffman code.
|
|
*
|
|
* @num_syms
|
|
* The number of symbols in the alphabet. The symbols are the
|
|
* integers in the range [0, num_syms - 1]. This parameter must be
|
|
* at least 2 and can't be greater than (1 << NUM_SYMBOL_BITS).
|
|
*
|
|
* @max_codeword_len
|
|
* The maximum permissible codeword length.
|
|
*
|
|
* @freqs
|
|
* An array of @num_syms entries, each of which specifies the
|
|
* frequency of the corresponding symbol. It is valid for some,
|
|
* none, or all of the frequencies to be 0.
|
|
*
|
|
* @lens
|
|
* An array of @num_syms entries in which this function will return
|
|
* the length, in bits, of the codeword assigned to each symbol.
|
|
* Symbols with 0 frequency will not have codewords per se, but
|
|
* their entries in this array will be set to 0. No lengths greater
|
|
* than @max_codeword_len will be assigned.
|
|
*
|
|
* @codewords
|
|
* An array of @num_syms entries in which this function will return
|
|
* the codeword for each symbol, right-justified and padded on the
|
|
* left with zeroes. Codewords for symbols with 0 frequency will be
|
|
* undefined.
|
|
*
|
|
* ---------------------------------------------------------------------
|
|
*
|
|
* This function builds a length-limited canonical Huffman code.
|
|
*
|
|
* A length-limited Huffman code contains no codewords longer than some
|
|
* specified length, and has exactly (with some algorithms) or
|
|
* approximately (with the algorithm used here) the minimum weighted path
|
|
* length from the root, given this constraint.
|
|
*
|
|
* A canonical Huffman code satisfies the properties that a longer
|
|
* codeword never lexicographically precedes a shorter codeword, and the
|
|
* lexicographic ordering of codewords of the same length is the same as
|
|
* the lexicographic ordering of the corresponding symbols. A canonical
|
|
* Huffman code, or more generally a canonical prefix code, can be
|
|
* reconstructed from only a list containing the codeword length of each
|
|
* symbol.
|
|
*
|
|
* The classic algorithm to generate a Huffman code creates a node for
|
|
* each symbol, then inserts these nodes into a min-heap keyed by symbol
|
|
* frequency. Then, repeatedly, the two lowest-frequency nodes are
|
|
* removed from the min-heap and added as the children of a new node
|
|
* having frequency equal to the sum of its two children, which is then
|
|
* inserted into the min-heap. When only a single node remains in the
|
|
* min-heap, it is the root of the Huffman tree. The codeword for each
|
|
* symbol is determined by the path needed to reach the corresponding
|
|
* node from the root. Descending to the left child appends a 0 bit,
|
|
* whereas descending to the right child appends a 1 bit.
|
|
*
|
|
* The classic algorithm is relatively easy to understand, but it is
|
|
* subject to a number of inefficiencies. In practice, it is fastest to
|
|
* first sort the symbols by frequency. (This itself can be subject to
|
|
* an optimization based on the fact that most frequencies tend to be
|
|
* low.) At the same time, we sort secondarily by symbol value, which
|
|
* aids the process of generating a canonical code. Then, during tree
|
|
* construction, no heap is necessary because both the leaf nodes and the
|
|
* unparented non-leaf nodes can be easily maintained in sorted order.
|
|
* Consequently, there can never be more than two possibilities for the
|
|
* next-lowest-frequency node.
|
|
*
|
|
* In addition, because we're generating a canonical code, we actually
|
|
* don't need the leaf nodes of the tree at all, only the non-leaf nodes.
|
|
* This is because for canonical code generation we don't need to know
|
|
* where the symbols are in the tree. Rather, we only need to know how
|
|
* many leaf nodes have each depth (codeword length). And this
|
|
* information can, in fact, be quickly generated from the tree of
|
|
* non-leaves only.
|
|
*
|
|
* Furthermore, we can build this stripped-down Huffman tree directly in
|
|
* the array in which the codewords are to be generated, provided that
|
|
* these array slots are large enough to hold a symbol and frequency
|
|
* value.
|
|
*
|
|
* Still furthermore, we don't even need to maintain explicit child
|
|
* pointers. We only need the parent pointers, and even those can be
|
|
* overwritten in-place with depth information as part of the process of
|
|
* extracting codeword lengths from the tree. So in summary, we do NOT
|
|
* need a big structure like:
|
|
*
|
|
* struct huffman_tree_node {
|
|
* unsigned int symbol;
|
|
* unsigned int frequency;
|
|
* unsigned int depth;
|
|
* struct huffman_tree_node *left_child;
|
|
* struct huffman_tree_node *right_child;
|
|
* };
|
|
*
|
|
*
|
|
* ... which often gets used in "naive" implementations of Huffman code
|
|
* generation.
|
|
*
|
|
* Many of these optimizations are based on the implementation in 7-Zip
|
|
* (source file: C/HuffEnc.c), which has been placed in the public domain
|
|
* by Igor Pavlov.
|
|
*/
|
|
static void
|
|
make_canonical_huffman_code(unsigned num_syms, unsigned max_codeword_len,
|
|
const u32 freqs[restrict],
|
|
u8 lens[restrict], u32 codewords[restrict])
|
|
{
|
|
u32 *A = codewords;
|
|
unsigned num_used_syms;
|
|
|
|
STATIC_ASSERT(DEFLATE_MAX_NUM_SYMS <= 1 << NUM_SYMBOL_BITS);
|
|
|
|
/* We begin by sorting the symbols primarily by frequency and
|
|
* secondarily by symbol value. As an optimization, the array
|
|
* used for this purpose ('A') shares storage with the space in
|
|
* which we will eventually return the codewords. */
|
|
|
|
num_used_syms = sort_symbols(num_syms, freqs, lens, A);
|
|
|
|
/* 'num_used_syms' is the number of symbols with nonzero
|
|
* frequency. This may be less than @num_syms. 'num_used_syms'
|
|
* is also the number of entries in 'A' that are valid. Each
|
|
* entry consists of a distinct symbol and a nonzero frequency
|
|
* packed into a 32-bit integer. */
|
|
|
|
/* Handle special cases where only 0 or 1 symbols were used (had
|
|
* nonzero frequency). */
|
|
|
|
if (unlikely(num_used_syms == 0)) {
|
|
/* Code is empty. sort_symbols() already set all lengths
|
|
* to 0, so there is nothing more to do. */
|
|
return;
|
|
}
|
|
|
|
if (unlikely(num_used_syms == 1)) {
|
|
/* Only one symbol was used, so we only need one
|
|
* codeword. But two codewords are needed to form the
|
|
* smallest complete Huffman code, which uses codewords 0
|
|
* and 1. Therefore, we choose another symbol to which
|
|
* to assign a codeword. We use 0 (if the used symbol is
|
|
* not 0) or 1 (if the used symbol is 0). In either
|
|
* case, the lesser-valued symbol must be assigned
|
|
* codeword 0 so that the resulting code is canonical. */
|
|
|
|
unsigned sym = A[0] & SYMBOL_MASK;
|
|
unsigned nonzero_idx = sym ? sym : 1;
|
|
|
|
codewords[0] = 0;
|
|
lens[0] = 1;
|
|
codewords[nonzero_idx] = 1;
|
|
lens[nonzero_idx] = 1;
|
|
return;
|
|
}
|
|
|
|
/* Build a stripped-down version of the Huffman tree, sharing the
|
|
* array 'A' with the symbol values. Then extract length counts
|
|
* from the tree and use them to generate the final codewords. */
|
|
|
|
build_tree(A, num_used_syms);
|
|
|
|
{
|
|
unsigned len_counts[DEFLATE_MAX_CODEWORD_LEN + 1];
|
|
|
|
compute_length_counts(A, num_used_syms - 2,
|
|
len_counts, max_codeword_len);
|
|
|
|
gen_codewords(A, lens, len_counts, max_codeword_len, num_syms);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clear the Huffman symbol frequency counters.
|
|
* This must be called when starting a new DEFLATE block.
|
|
*/
|
|
static void
|
|
deflate_reset_symbol_frequencies(struct libdeflate_compressor *c)
|
|
{
|
|
memset(&c->freqs, 0, sizeof(c->freqs));
|
|
}
|
|
|
|
/* Reverse the Huffman codeword 'codeword', which is 'len' bits in length. */
|
|
static u32
|
|
deflate_reverse_codeword(u32 codeword, u8 len)
|
|
{
|
|
/* The following branchless algorithm is faster than going bit by bit.
|
|
* Note: since no codewords are longer than 16 bits, we only need to
|
|
* reverse the low 16 bits of the 'u32'. */
|
|
STATIC_ASSERT(DEFLATE_MAX_CODEWORD_LEN <= 16);
|
|
|
|
/* Flip adjacent 1-bit fields */
|
|
codeword = ((codeword & 0x5555) << 1) | ((codeword & 0xAAAA) >> 1);
|
|
|
|
/* Flip adjacent 2-bit fields */
|
|
codeword = ((codeword & 0x3333) << 2) | ((codeword & 0xCCCC) >> 2);
|
|
|
|
/* Flip adjacent 4-bit fields */
|
|
codeword = ((codeword & 0x0F0F) << 4) | ((codeword & 0xF0F0) >> 4);
|
|
|
|
/* Flip adjacent 8-bit fields */
|
|
codeword = ((codeword & 0x00FF) << 8) | ((codeword & 0xFF00) >> 8);
|
|
|
|
/* Return the high 'len' bits of the bit-reversed 16 bit value. */
|
|
return codeword >> (16 - len);
|
|
}
|
|
|
|
/* Make a canonical Huffman code with bit-reversed codewords. */
|
|
static void
|
|
deflate_make_huffman_code(unsigned num_syms, unsigned max_codeword_len,
|
|
const u32 freqs[], u8 lens[], u32 codewords[])
|
|
{
|
|
unsigned sym;
|
|
|
|
make_canonical_huffman_code(num_syms, max_codeword_len,
|
|
freqs, lens, codewords);
|
|
|
|
for (sym = 0; sym < num_syms; sym++)
|
|
codewords[sym] = deflate_reverse_codeword(codewords[sym], lens[sym]);
|
|
}
|
|
|
|
/*
|
|
* Build the literal/length and offset Huffman codes for a DEFLATE block.
|
|
*
|
|
* This takes as input the frequency tables for each code and produces as output
|
|
* a set of tables that map symbols to codewords and codeword lengths.
|
|
*/
|
|
static void
|
|
deflate_make_huffman_codes(const struct deflate_freqs *freqs,
|
|
struct deflate_codes *codes)
|
|
{
|
|
STATIC_ASSERT(MAX_LITLEN_CODEWORD_LEN <= DEFLATE_MAX_LITLEN_CODEWORD_LEN);
|
|
STATIC_ASSERT(MAX_OFFSET_CODEWORD_LEN <= DEFLATE_MAX_OFFSET_CODEWORD_LEN);
|
|
|
|
deflate_make_huffman_code(DEFLATE_NUM_LITLEN_SYMS,
|
|
MAX_LITLEN_CODEWORD_LEN,
|
|
freqs->litlen,
|
|
codes->lens.litlen,
|
|
codes->codewords.litlen);
|
|
|
|
deflate_make_huffman_code(DEFLATE_NUM_OFFSET_SYMS,
|
|
MAX_OFFSET_CODEWORD_LEN,
|
|
freqs->offset,
|
|
codes->lens.offset,
|
|
codes->codewords.offset);
|
|
}
|
|
|
|
/* Initialize c->static_codes. */
|
|
static void
|
|
deflate_init_static_codes(struct libdeflate_compressor *c)
|
|
{
|
|
unsigned i;
|
|
|
|
for (i = 0; i < 144; i++)
|
|
c->freqs.litlen[i] = 1 << (9 - 8);
|
|
for (; i < 256; i++)
|
|
c->freqs.litlen[i] = 1 << (9 - 9);
|
|
for (; i < 280; i++)
|
|
c->freqs.litlen[i] = 1 << (9 - 7);
|
|
for (; i < 288; i++)
|
|
c->freqs.litlen[i] = 1 << (9 - 8);
|
|
|
|
for (i = 0; i < 32; i++)
|
|
c->freqs.offset[i] = 1 << (5 - 5);
|
|
|
|
deflate_make_huffman_codes(&c->freqs, &c->static_codes);
|
|
}
|
|
|
|
/* Return the offset slot for the specified match offset. */
|
|
static forceinline unsigned
|
|
deflate_get_offset_slot(struct libdeflate_compressor *c, unsigned offset)
|
|
{
|
|
#if USE_FULL_OFFSET_SLOT_FAST
|
|
return c->offset_slot_fast[offset];
|
|
#else
|
|
if (offset <= 256)
|
|
return c->offset_slot_fast[offset - 1];
|
|
else
|
|
return c->offset_slot_fast[256 + ((offset - 1) >> 7)];
|
|
#endif
|
|
}
|
|
|
|
/* Write the header fields common to all DEFLATE block types. */
|
|
static void
|
|
deflate_write_block_header(struct deflate_output_bitstream *os,
|
|
bool is_final_block, unsigned block_type)
|
|
{
|
|
deflate_add_bits(os, is_final_block, 1);
|
|
deflate_add_bits(os, block_type, 2);
|
|
deflate_flush_bits(os);
|
|
}
|
|
|
|
static unsigned
|
|
deflate_compute_precode_items(const u8 lens[restrict],
|
|
const unsigned num_lens,
|
|
u32 precode_freqs[restrict],
|
|
unsigned precode_items[restrict])
|
|
{
|
|
unsigned *itemptr;
|
|
unsigned run_start;
|
|
unsigned run_end;
|
|
unsigned extra_bits;
|
|
u8 len;
|
|
|
|
memset(precode_freqs, 0,
|
|
DEFLATE_NUM_PRECODE_SYMS * sizeof(precode_freqs[0]));
|
|
|
|
itemptr = precode_items;
|
|
run_start = 0;
|
|
do {
|
|
/* Find the next run of codeword lengths. */
|
|
|
|
/* len = the length being repeated */
|
|
len = lens[run_start];
|
|
|
|
/* Extend the run. */
|
|
run_end = run_start;
|
|
do {
|
|
run_end++;
|
|
} while (run_end != num_lens && len == lens[run_end]);
|
|
|
|
if (len == 0) {
|
|
/* Run of zeroes. */
|
|
|
|
/* Symbol 18: RLE 11 to 138 zeroes at a time. */
|
|
while ((run_end - run_start) >= 11) {
|
|
extra_bits = MIN((run_end - run_start) - 11, 0x7F);
|
|
precode_freqs[18]++;
|
|
*itemptr++ = 18 | (extra_bits << 5);
|
|
run_start += 11 + extra_bits;
|
|
}
|
|
|
|
/* Symbol 17: RLE 3 to 10 zeroes at a time. */
|
|
if ((run_end - run_start) >= 3) {
|
|
extra_bits = MIN((run_end - run_start) - 3, 0x7);
|
|
precode_freqs[17]++;
|
|
*itemptr++ = 17 | (extra_bits << 5);
|
|
run_start += 3 + extra_bits;
|
|
}
|
|
} else {
|
|
|
|
/* A run of nonzero lengths. */
|
|
|
|
/* Symbol 16: RLE 3 to 6 of the previous length. */
|
|
if ((run_end - run_start) >= 4) {
|
|
precode_freqs[len]++;
|
|
*itemptr++ = len;
|
|
run_start++;
|
|
do {
|
|
extra_bits = MIN((run_end - run_start) - 3, 0x3);
|
|
precode_freqs[16]++;
|
|
*itemptr++ = 16 | (extra_bits << 5);
|
|
run_start += 3 + extra_bits;
|
|
} while ((run_end - run_start) >= 3);
|
|
}
|
|
}
|
|
|
|
/* Output any remaining lengths without RLE. */
|
|
while (run_start != run_end) {
|
|
precode_freqs[len]++;
|
|
*itemptr++ = len;
|
|
run_start++;
|
|
}
|
|
} while (run_start != num_lens);
|
|
|
|
return itemptr - precode_items;
|
|
}
|
|
|
|
/*
|
|
* Huffman codeword lengths for dynamic Huffman blocks are compressed using a
|
|
* separate Huffman code, the "precode", which contains a symbol for each
|
|
* possible codeword length in the larger code as well as several special
|
|
* symbols to represent repeated codeword lengths (a form of run-length
|
|
* encoding). The precode is itself constructed in canonical form, and its
|
|
* codeword lengths are represented literally in 19 3-bit fields that
|
|
* immediately precede the compressed codeword lengths of the larger code.
|
|
*/
|
|
|
|
/* Precompute the information needed to output Huffman codes. */
|
|
static void
|
|
deflate_precompute_huffman_header(struct libdeflate_compressor *c)
|
|
{
|
|
/* Compute how many litlen and offset symbols are needed. */
|
|
|
|
for (c->num_litlen_syms = DEFLATE_NUM_LITLEN_SYMS;
|
|
c->num_litlen_syms > 257;
|
|
c->num_litlen_syms--)
|
|
if (c->codes.lens.litlen[c->num_litlen_syms - 1] != 0)
|
|
break;
|
|
|
|
for (c->num_offset_syms = DEFLATE_NUM_OFFSET_SYMS;
|
|
c->num_offset_syms > 1;
|
|
c->num_offset_syms--)
|
|
if (c->codes.lens.offset[c->num_offset_syms - 1] != 0)
|
|
break;
|
|
|
|
/* If we're not using the full set of literal/length codeword lengths,
|
|
* then temporarily move the offset codeword lengths over so that the
|
|
* literal/length and offset codeword lengths are contiguous. */
|
|
|
|
STATIC_ASSERT(offsetof(struct deflate_lens, offset) ==
|
|
DEFLATE_NUM_LITLEN_SYMS);
|
|
|
|
if (c->num_litlen_syms != DEFLATE_NUM_LITLEN_SYMS) {
|
|
memmove((u8 *)&c->codes.lens + c->num_litlen_syms,
|
|
(u8 *)&c->codes.lens + DEFLATE_NUM_LITLEN_SYMS,
|
|
c->num_offset_syms);
|
|
}
|
|
|
|
/* Compute the "items" (RLE / literal tokens and extra bits) with which
|
|
* the codeword lengths in the larger code will be output. */
|
|
c->num_precode_items =
|
|
deflate_compute_precode_items((u8 *)&c->codes.lens,
|
|
c->num_litlen_syms +
|
|
c->num_offset_syms,
|
|
c->precode_freqs,
|
|
c->precode_items);
|
|
|
|
/* Build the precode. */
|
|
STATIC_ASSERT(MAX_PRE_CODEWORD_LEN <= DEFLATE_MAX_PRE_CODEWORD_LEN);
|
|
deflate_make_huffman_code(DEFLATE_NUM_PRECODE_SYMS,
|
|
MAX_PRE_CODEWORD_LEN,
|
|
c->precode_freqs, c->precode_lens,
|
|
c->precode_codewords);
|
|
|
|
/* Count how many precode lengths we actually need to output. */
|
|
for (c->num_explicit_lens = DEFLATE_NUM_PRECODE_SYMS;
|
|
c->num_explicit_lens > 4;
|
|
c->num_explicit_lens--)
|
|
if (c->precode_lens[deflate_precode_lens_permutation[
|
|
c->num_explicit_lens - 1]] != 0)
|
|
break;
|
|
|
|
/* Restore the offset codeword lengths if needed. */
|
|
if (c->num_litlen_syms != DEFLATE_NUM_LITLEN_SYMS) {
|
|
memmove((u8 *)&c->codes.lens + DEFLATE_NUM_LITLEN_SYMS,
|
|
(u8 *)&c->codes.lens + c->num_litlen_syms,
|
|
c->num_offset_syms);
|
|
}
|
|
}
|
|
|
|
/* Output the Huffman codes. */
|
|
static void
|
|
deflate_write_huffman_header(struct libdeflate_compressor *c,
|
|
struct deflate_output_bitstream *os)
|
|
{
|
|
unsigned i;
|
|
|
|
deflate_add_bits(os, c->num_litlen_syms - 257, 5);
|
|
deflate_add_bits(os, c->num_offset_syms - 1, 5);
|
|
deflate_add_bits(os, c->num_explicit_lens - 4, 4);
|
|
deflate_flush_bits(os);
|
|
|
|
/* Output the lengths of the codewords in the precode. */
|
|
for (i = 0; i < c->num_explicit_lens; i++) {
|
|
deflate_add_bits(os, c->precode_lens[
|
|
deflate_precode_lens_permutation[i]], 3);
|
|
deflate_flush_bits(os);
|
|
}
|
|
|
|
/* Output the encoded lengths of the codewords in the larger code. */
|
|
for (i = 0; i < c->num_precode_items; i++) {
|
|
unsigned precode_item = c->precode_items[i];
|
|
unsigned precode_sym = precode_item & 0x1F;
|
|
deflate_add_bits(os, c->precode_codewords[precode_sym],
|
|
c->precode_lens[precode_sym]);
|
|
if (precode_sym >= 16) {
|
|
if (precode_sym == 16)
|
|
deflate_add_bits(os, precode_item >> 5, 2);
|
|
else if (precode_sym == 17)
|
|
deflate_add_bits(os, precode_item >> 5, 3);
|
|
else
|
|
deflate_add_bits(os, precode_item >> 5, 7);
|
|
}
|
|
STATIC_ASSERT(CAN_BUFFER(DEFLATE_MAX_PRE_CODEWORD_LEN + 7));
|
|
deflate_flush_bits(os);
|
|
}
|
|
}
|
|
|
|
static void
|
|
deflate_write_sequences(struct deflate_output_bitstream * restrict os,
|
|
const struct deflate_codes * restrict codes,
|
|
const struct deflate_sequence sequences[restrict],
|
|
const u8 * restrict in_next)
|
|
{
|
|
const struct deflate_sequence *seq = sequences;
|
|
|
|
for (;;) {
|
|
u32 litrunlen = seq->litrunlen_and_length & 0x7FFFFF;
|
|
unsigned length = seq->litrunlen_and_length >> 23;
|
|
unsigned length_slot;
|
|
unsigned litlen_symbol;
|
|
unsigned offset_symbol;
|
|
|
|
if (litrunlen) {
|
|
#if 1
|
|
while (litrunlen >= 4) {
|
|
unsigned lit0 = in_next[0];
|
|
unsigned lit1 = in_next[1];
|
|
unsigned lit2 = in_next[2];
|
|
unsigned lit3 = in_next[3];
|
|
|
|
deflate_add_bits(os, codes->codewords.litlen[lit0],
|
|
codes->lens.litlen[lit0]);
|
|
if (!CAN_BUFFER(2 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
|
|
deflate_add_bits(os, codes->codewords.litlen[lit1],
|
|
codes->lens.litlen[lit1]);
|
|
if (!CAN_BUFFER(4 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
|
|
deflate_add_bits(os, codes->codewords.litlen[lit2],
|
|
codes->lens.litlen[lit2]);
|
|
if (!CAN_BUFFER(2 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
|
|
deflate_add_bits(os, codes->codewords.litlen[lit3],
|
|
codes->lens.litlen[lit3]);
|
|
deflate_flush_bits(os);
|
|
in_next += 4;
|
|
litrunlen -= 4;
|
|
}
|
|
if (litrunlen-- != 0) {
|
|
deflate_add_bits(os, codes->codewords.litlen[*in_next],
|
|
codes->lens.litlen[*in_next]);
|
|
if (!CAN_BUFFER(3 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
in_next++;
|
|
if (litrunlen-- != 0) {
|
|
deflate_add_bits(os, codes->codewords.litlen[*in_next],
|
|
codes->lens.litlen[*in_next]);
|
|
if (!CAN_BUFFER(3 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
in_next++;
|
|
if (litrunlen-- != 0) {
|
|
deflate_add_bits(os, codes->codewords.litlen[*in_next],
|
|
codes->lens.litlen[*in_next]);
|
|
if (!CAN_BUFFER(3 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
in_next++;
|
|
}
|
|
}
|
|
if (CAN_BUFFER(3 * MAX_LITLEN_CODEWORD_LEN))
|
|
deflate_flush_bits(os);
|
|
}
|
|
#else
|
|
do {
|
|
unsigned lit = *in_next++;
|
|
deflate_add_bits(os, codes->codewords.litlen[lit],
|
|
codes->lens.litlen[lit]);
|
|
deflate_flush_bits(os);
|
|
} while (--litrunlen);
|
|
#endif
|
|
}
|
|
|
|
if (length == 0)
|
|
return;
|
|
|
|
in_next += length;
|
|
|
|
length_slot = seq->length_slot;
|
|
litlen_symbol = DEFLATE_FIRST_LEN_SYM + length_slot;
|
|
|
|
/* Litlen symbol */
|
|
deflate_add_bits(os, codes->codewords.litlen[litlen_symbol],
|
|
codes->lens.litlen[litlen_symbol]);
|
|
|
|
/* Extra length bits */
|
|
STATIC_ASSERT(CAN_BUFFER(MAX_LITLEN_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_LENGTH_BITS));
|
|
deflate_add_bits(os, length - deflate_length_slot_base[length_slot],
|
|
deflate_extra_length_bits[length_slot]);
|
|
|
|
if (!CAN_BUFFER(MAX_LITLEN_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_LENGTH_BITS +
|
|
MAX_OFFSET_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_OFFSET_BITS))
|
|
deflate_flush_bits(os);
|
|
|
|
/* Offset symbol */
|
|
offset_symbol = seq->offset_symbol;
|
|
deflate_add_bits(os, codes->codewords.offset[offset_symbol],
|
|
codes->lens.offset[offset_symbol]);
|
|
|
|
if (!CAN_BUFFER(MAX_OFFSET_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_OFFSET_BITS))
|
|
deflate_flush_bits(os);
|
|
|
|
/* Extra offset bits */
|
|
deflate_add_bits(os, seq->offset - deflate_offset_slot_base[offset_symbol],
|
|
deflate_extra_offset_bits[offset_symbol]);
|
|
|
|
deflate_flush_bits(os);
|
|
|
|
seq++;
|
|
}
|
|
}
|
|
|
|
#if SUPPORT_NEAR_OPTIMAL_PARSING
|
|
/*
|
|
* Follow the minimum-cost path in the graph of possible match/literal choices
|
|
* for the current block and write out the matches/literals using the specified
|
|
* Huffman codes.
|
|
*
|
|
* Note: this is slightly duplicated with deflate_write_sequences(), the reason
|
|
* being that we don't want to waste time translating between intermediate
|
|
* match/literal representations.
|
|
*/
|
|
static void
|
|
deflate_write_item_list(struct deflate_output_bitstream *os,
|
|
const struct deflate_codes *codes,
|
|
struct libdeflate_compressor *c,
|
|
u32 block_length)
|
|
{
|
|
struct deflate_optimum_node *cur_node = &c->p.n.optimum_nodes[0];
|
|
struct deflate_optimum_node * const end_node = &c->p.n.optimum_nodes[block_length];
|
|
do {
|
|
unsigned length = cur_node->item & OPTIMUM_LEN_MASK;
|
|
unsigned offset = cur_node->item >> OPTIMUM_OFFSET_SHIFT;
|
|
unsigned litlen_symbol;
|
|
unsigned length_slot;
|
|
unsigned offset_slot;
|
|
|
|
if (length == 1) {
|
|
/* Literal */
|
|
litlen_symbol = offset;
|
|
deflate_add_bits(os, codes->codewords.litlen[litlen_symbol],
|
|
codes->lens.litlen[litlen_symbol]);
|
|
deflate_flush_bits(os);
|
|
} else {
|
|
/* Match length */
|
|
length_slot = deflate_length_slot[length];
|
|
litlen_symbol = DEFLATE_FIRST_LEN_SYM + length_slot;
|
|
deflate_add_bits(os, codes->codewords.litlen[litlen_symbol],
|
|
codes->lens.litlen[litlen_symbol]);
|
|
|
|
deflate_add_bits(os, length - deflate_length_slot_base[length_slot],
|
|
deflate_extra_length_bits[length_slot]);
|
|
|
|
if (!CAN_BUFFER(MAX_LITLEN_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_LENGTH_BITS +
|
|
MAX_OFFSET_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_OFFSET_BITS))
|
|
deflate_flush_bits(os);
|
|
|
|
|
|
/* Match offset */
|
|
offset_slot = deflate_get_offset_slot(c, offset);
|
|
deflate_add_bits(os, codes->codewords.offset[offset_slot],
|
|
codes->lens.offset[offset_slot]);
|
|
|
|
if (!CAN_BUFFER(MAX_OFFSET_CODEWORD_LEN +
|
|
DEFLATE_MAX_EXTRA_OFFSET_BITS))
|
|
deflate_flush_bits(os);
|
|
|
|
deflate_add_bits(os, offset - deflate_offset_slot_base[offset_slot],
|
|
deflate_extra_offset_bits[offset_slot]);
|
|
|
|
deflate_flush_bits(os);
|
|
}
|
|
cur_node += length;
|
|
} while (cur_node != end_node);
|
|
}
|
|
#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
|
|
|
|
/* Output the end-of-block symbol. */
|
|
static void
|
|
deflate_write_end_of_block(struct deflate_output_bitstream *os,
|
|
const struct deflate_codes *codes)
|
|
{
|
|
deflate_add_bits(os, codes->codewords.litlen[DEFLATE_END_OF_BLOCK],
|
|
codes->lens.litlen[DEFLATE_END_OF_BLOCK]);
|
|
deflate_flush_bits(os);
|
|
}
|
|
|
|
static void
|
|
deflate_write_uncompressed_block(struct deflate_output_bitstream *os,
|
|
const u8 *data, u16 len,
|
|
bool is_final_block)
|
|
{
|
|
deflate_write_block_header(os, is_final_block,
|
|
DEFLATE_BLOCKTYPE_UNCOMPRESSED);
|
|
deflate_align_bitstream(os);
|
|
|
|
if (4 + (u32)len >= os->end - os->next) {
|
|
os->next = os->end;
|
|
return;
|
|
}
|
|
|
|
put_unaligned_le16(len, os->next);
|
|
os->next += 2;
|
|
put_unaligned_le16(~len, os->next);
|
|
os->next += 2;
|
|
memcpy(os->next, data, len);
|
|
os->next += len;
|
|
}
|
|
|
|
static void
|
|
deflate_write_uncompressed_blocks(struct deflate_output_bitstream *os,
|
|
const u8 *data, size_t data_length,
|
|
bool is_final_block)
|
|
{
|
|
do {
|
|
u16 len = MIN(data_length, UINT16_MAX);
|
|
|
|
deflate_write_uncompressed_block(os, data, len,
|
|
is_final_block && len == data_length);
|
|
data += len;
|
|
data_length -= len;
|
|
} while (data_length != 0);
|
|
}
|
|
|
|
/*
|
|
* Choose the best type of block to use (dynamic Huffman, static Huffman, or
|
|
* uncompressed), then output it.
|
|
*/
|
|
static void
|
|
deflate_flush_block(struct libdeflate_compressor * restrict c,
|
|
struct deflate_output_bitstream * restrict os,
|
|
const u8 * restrict block_begin, u32 block_length,
|
|
bool is_final_block, bool use_item_list)
|
|
{
|
|
static const u8 deflate_extra_precode_bits[DEFLATE_NUM_PRECODE_SYMS] = {
|
|
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 3, 7,
|
|
};
|
|
|
|
/* Costs are measured in bits */
|
|
u32 dynamic_cost = 0;
|
|
u32 static_cost = 0;
|
|
u32 uncompressed_cost = 0;
|
|
struct deflate_codes *codes;
|
|
int block_type;
|
|
unsigned sym;
|
|
|
|
/* Tally the end-of-block symbol. */
|
|
c->freqs.litlen[DEFLATE_END_OF_BLOCK]++;
|
|
|
|
/* Build dynamic Huffman codes. */
|
|
deflate_make_huffman_codes(&c->freqs, &c->codes);
|
|
|
|
/* Account for the cost of sending dynamic Huffman codes. */
|
|
deflate_precompute_huffman_header(c);
|
|
dynamic_cost += 5 + 5 + 4 + (3 * c->num_explicit_lens);
|
|
for (sym = 0; sym < DEFLATE_NUM_PRECODE_SYMS; sym++) {
|
|
u32 extra = deflate_extra_precode_bits[sym];
|
|
dynamic_cost += c->precode_freqs[sym] *
|
|
(extra + c->precode_lens[sym]);
|
|
}
|
|
|
|
/* Account for the cost of encoding literals. */
|
|
for (sym = 0; sym < 256; sym++) {
|
|
dynamic_cost += c->freqs.litlen[sym] *
|
|
c->codes.lens.litlen[sym];
|
|
}
|
|
for (sym = 0; sym < 144; sym++)
|
|
static_cost += c->freqs.litlen[sym] * 8;
|
|
for (; sym < 256; sym++)
|
|
static_cost += c->freqs.litlen[sym] * 9;
|
|
|
|
/* Account for the cost of encoding the end-of-block symbol. */
|
|
dynamic_cost += c->codes.lens.litlen[DEFLATE_END_OF_BLOCK];
|
|
static_cost += 7;
|
|
|
|
/* Account for the cost of encoding lengths. */
|
|
for (sym = DEFLATE_FIRST_LEN_SYM;
|
|
sym < DEFLATE_FIRST_LEN_SYM + ARRAY_LEN(deflate_extra_length_bits);
|
|
sym++) {
|
|
u32 extra = deflate_extra_length_bits[
|
|
sym - DEFLATE_FIRST_LEN_SYM];
|
|
dynamic_cost += c->freqs.litlen[sym] *
|
|
(extra + c->codes.lens.litlen[sym]);
|
|
static_cost += c->freqs.litlen[sym] *
|
|
(extra + c->static_codes.lens.litlen[sym]);
|
|
}
|
|
|
|
/* Account for the cost of encoding offsets. */
|
|
for (sym = 0; sym < ARRAY_LEN(deflate_extra_offset_bits); sym++) {
|
|
u32 extra = deflate_extra_offset_bits[sym];
|
|
dynamic_cost += c->freqs.offset[sym] *
|
|
(extra + c->codes.lens.offset[sym]);
|
|
static_cost += c->freqs.offset[sym] * (extra + 5);
|
|
}
|
|
|
|
/* Compute the cost of using uncompressed blocks. */
|
|
uncompressed_cost += (-(os->bitcount + 3) & 7) + 32 +
|
|
(40 * (DIV_ROUND_UP(block_length,
|
|
UINT16_MAX) - 1)) +
|
|
(8 * block_length);
|
|
|
|
/* Choose the cheapest block type. */
|
|
if (dynamic_cost < MIN(static_cost, uncompressed_cost)) {
|
|
block_type = DEFLATE_BLOCKTYPE_DYNAMIC_HUFFMAN;
|
|
codes = &c->codes;
|
|
} else if (static_cost < uncompressed_cost) {
|
|
block_type = DEFLATE_BLOCKTYPE_STATIC_HUFFMAN;
|
|
codes = &c->static_codes;
|
|
} else {
|
|
block_type = DEFLATE_BLOCKTYPE_UNCOMPRESSED;
|
|
}
|
|
|
|
/* Now actually output the block. */
|
|
|
|
if (block_type == DEFLATE_BLOCKTYPE_UNCOMPRESSED) {
|
|
/* Note: the length being flushed may exceed the maximum length
|
|
* of an uncompressed block (65535 bytes). Therefore, more than
|
|
* one uncompressed block might be needed. */
|
|
deflate_write_uncompressed_blocks(os, block_begin, block_length,
|
|
is_final_block);
|
|
} else {
|
|
/* Output the block header. */
|
|
deflate_write_block_header(os, is_final_block, block_type);
|
|
|
|
/* Output the Huffman codes (dynamic Huffman blocks only). */
|
|
if (block_type == DEFLATE_BLOCKTYPE_DYNAMIC_HUFFMAN)
|
|
deflate_write_huffman_header(c, os);
|
|
|
|
/* Output the literals, matches, and end-of-block symbol. */
|
|
#if SUPPORT_NEAR_OPTIMAL_PARSING
|
|
if (use_item_list)
|
|
deflate_write_item_list(os, codes, c, block_length);
|
|
else
|
|
#endif
|
|
deflate_write_sequences(os, codes, c->p.g.sequences,
|
|
block_begin);
|
|
deflate_write_end_of_block(os, codes);
|
|
}
|
|
}
|
|
|
|
static forceinline void
|
|
deflate_choose_literal(struct libdeflate_compressor *c, unsigned literal,
|
|
u32 *litrunlen_p)
|
|
{
|
|
c->freqs.litlen[literal]++;
|
|
++*litrunlen_p;
|
|
}
|
|
|
|
static forceinline void
|
|
deflate_choose_match(struct libdeflate_compressor *c,
|
|
unsigned length, unsigned offset,
|
|
u32 *litrunlen_p, struct deflate_sequence **next_seq_p)
|
|
{
|
|
struct deflate_sequence *seq = *next_seq_p;
|
|
unsigned length_slot = deflate_length_slot[length];
|
|
unsigned offset_slot = deflate_get_offset_slot(c, offset);
|
|
|
|
c->freqs.litlen[DEFLATE_FIRST_LEN_SYM + length_slot]++;
|
|
c->freqs.offset[offset_slot]++;
|
|
|
|
seq->litrunlen_and_length = ((u32)length << 23) | *litrunlen_p;
|
|
seq->offset = offset;
|
|
seq->length_slot = length_slot;
|
|
seq->offset_symbol = offset_slot;
|
|
|
|
*litrunlen_p = 0;
|
|
*next_seq_p = seq + 1;
|
|
}
|
|
|
|
static forceinline void
|
|
deflate_finish_sequence(struct deflate_sequence *seq, u32 litrunlen)
|
|
{
|
|
seq->litrunlen_and_length = litrunlen; /* length = 0 */
|
|
}
|
|
|
|
/******************************************************************************/
|
|
|
|
/*
|
|
* Block splitting algorithm. The problem is to decide when it is worthwhile to
|
|
* start a new block with new Huffman codes. There is a theoretically optimal
|
|
* solution: recursively consider every possible block split, considering the
|
|
* exact cost of each block, and choose the minimum cost approach. But this is
|
|
* far too slow. Instead, as an approximation, we can count symbols and after
|
|
* every N symbols, compare the expected distribution of symbols based on the
|
|
* previous data with the actual distribution. If they differ "by enough", then
|
|
* start a new block.
|
|
*
|
|
* As an optimization and heuristic, we don't distinguish between every symbol
|
|
* but rather we combine many symbols into a single "observation type". For
|
|
* literals we only look at the high bits and low bits, and for matches we only
|
|
* look at whether the match is long or not. The assumption is that for typical
|
|
* "real" data, places that are good block boundaries will tend to be noticeable
|
|
* based only on changes in these aggregate frequencies, without looking for
|
|
* subtle differences in individual symbols. For example, a change from ASCII
|
|
* bytes to non-ASCII bytes, or from few matches (generally less compressible)
|
|
* to many matches (generally more compressible), would be easily noticed based
|
|
* on the aggregates.
|
|
*
|
|
* For determining whether the frequency distributions are "different enough" to
|
|
* start a new block, the simply heuristic of splitting when the sum of absolute
|
|
* differences exceeds a constant seems to be good enough. We also add a number
|
|
* proportional to the block length so that the algorithm is more likely to end
|
|
* long blocks than short blocks. This reflects the general expectation that it
|
|
* will become increasingly beneficial to start a new block as the current
|
|
* block grows longer.
|
|
*
|
|
* Finally, for an approximation, it is not strictly necessary that the exact
|
|
* symbols being used are considered. With "near-optimal parsing", for example,
|
|
* the actual symbols that will be used are unknown until after the block
|
|
* boundary is chosen and the block has been optimized. Since the final choices
|
|
* cannot be used, we can use preliminary "greedy" choices instead.
|
|
*/
|
|
|
|
/* Initialize the block split statistics when starting a new block. */
|
|
static void
|
|
init_block_split_stats(struct block_split_stats *stats)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < NUM_OBSERVATION_TYPES; i++) {
|
|
stats->new_observations[i] = 0;
|
|
stats->observations[i] = 0;
|
|
}
|
|
stats->num_new_observations = 0;
|
|
stats->num_observations = 0;
|
|
}
|
|
|
|
/* Literal observation. Heuristic: use the top 2 bits and low 1 bits of the
|
|
* literal, for 8 possible literal observation types. */
|
|
static forceinline void
|
|
observe_literal(struct block_split_stats *stats, u8 lit)
|
|
{
|
|
stats->new_observations[((lit >> 5) & 0x6) | (lit & 1)]++;
|
|
stats->num_new_observations++;
|
|
}
|
|
|
|
/* Match observation. Heuristic: use one observation type for "short match" and
|
|
* one observation type for "long match". */
|
|
static forceinline void
|
|
observe_match(struct block_split_stats *stats, unsigned length)
|
|
{
|
|
stats->new_observations[NUM_LITERAL_OBSERVATION_TYPES + (length >= 9)]++;
|
|
stats->num_new_observations++;
|
|
}
|
|
|
|
static bool
|
|
do_end_block_check(struct block_split_stats *stats, u32 block_length)
|
|
{
|
|
int i;
|
|
|
|
if (stats->num_observations > 0) {
|
|
|
|
/* Note: to avoid slow divisions, we do not divide by
|
|
* 'num_observations', but rather do all math with the numbers
|
|
* multiplied by 'num_observations'. */
|
|
u32 total_delta = 0;
|
|
for (i = 0; i < NUM_OBSERVATION_TYPES; i++) {
|
|
u32 expected = stats->observations[i] * stats->num_new_observations;
|
|
u32 actual = stats->new_observations[i] * stats->num_observations;
|
|
u32 delta = (actual > expected) ? actual - expected :
|
|
expected - actual;
|
|
total_delta += delta;
|
|
}
|
|
|
|
/* Ready to end the block? */
|
|
if (total_delta + (block_length / 4096) * stats->num_observations >=
|
|
NUM_OBSERVATIONS_PER_BLOCK_CHECK * 200 / 512 * stats->num_observations)
|
|
return true;
|
|
}
|
|
|
|
for (i = 0; i < NUM_OBSERVATION_TYPES; i++) {
|
|
stats->observations[i] += stats->new_observations[i];
|
|
stats->new_observations[i] = 0;
|
|
}
|
|
stats->num_observations += stats->num_new_observations;
|
|
stats->num_new_observations = 0;
|
|
return false;
|
|
}
|
|
|
|
static forceinline bool
|
|
should_end_block(struct block_split_stats *stats,
|
|
const u8 *in_block_begin, const u8 *in_next, const u8 *in_end)
|
|
{
|
|
/* Ready to check block split statistics? */
|
|
if (stats->num_new_observations < NUM_OBSERVATIONS_PER_BLOCK_CHECK ||
|
|
in_next - in_block_begin < MIN_BLOCK_LENGTH ||
|
|
in_end - in_next < MIN_BLOCK_LENGTH)
|
|
return false;
|
|
|
|
return do_end_block_check(stats, in_next - in_block_begin);
|
|
}
|
|
|
|
/******************************************************************************/
|
|
|
|
/*
|
|
* Decrease the maximum and nice match lengths if we're approaching the end of
|
|
* the input buffer.
|
|
*/
|
|
static forceinline void
|
|
adjust_max_and_nice_len(unsigned *max_len, unsigned *nice_len, size_t remaining)
|
|
{
|
|
if (unlikely(remaining < DEFLATE_MAX_MATCH_LEN)) {
|
|
*max_len = remaining;
|
|
*nice_len = MIN(*nice_len, *max_len);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* This is the level 0 "compressor". It always outputs uncompressed blocks.
|
|
*/
|
|
static size_t
|
|
deflate_compress_none(struct libdeflate_compressor * restrict c,
|
|
const u8 * restrict in, size_t in_nbytes,
|
|
u8 * restrict out, size_t out_nbytes_avail)
|
|
{
|
|
struct deflate_output_bitstream os;
|
|
|
|
deflate_init_output(&os, out, out_nbytes_avail);
|
|
|
|
deflate_write_uncompressed_blocks(&os, in, in_nbytes, true);
|
|
|
|
return deflate_flush_output(&os);
|
|
}
|
|
|
|
/*
|
|
* This is the "greedy" DEFLATE compressor. It always chooses the longest match.
|
|
*/
|
|
static size_t
|
|
deflate_compress_greedy(struct libdeflate_compressor * restrict c,
|
|
const u8 * restrict in, size_t in_nbytes,
|
|
u8 * restrict out, size_t out_nbytes_avail)
|
|
{
|
|
const u8 *in_next = in;
|
|
const u8 *in_end = in_next + in_nbytes;
|
|
struct deflate_output_bitstream os;
|
|
const u8 *in_cur_base = in_next;
|
|
unsigned max_len = DEFLATE_MAX_MATCH_LEN;
|
|
unsigned nice_len = MIN(c->nice_match_length, max_len);
|
|
u32 next_hashes[2] = {0, 0};
|
|
|
|
deflate_init_output(&os, out, out_nbytes_avail);
|
|
hc_matchfinder_init(&c->p.g.hc_mf);
|
|
|
|
do {
|
|
/* Starting a new DEFLATE block. */
|
|
|
|
const u8 * const in_block_begin = in_next;
|
|
const u8 * const in_max_block_end =
|
|
in_next + MIN(in_end - in_next, SOFT_MAX_BLOCK_LENGTH);
|
|
u32 litrunlen = 0;
|
|
struct deflate_sequence *next_seq = c->p.g.sequences;
|
|
|
|
init_block_split_stats(&c->split_stats);
|
|
deflate_reset_symbol_frequencies(c);
|
|
|
|
do {
|
|
u32 length;
|
|
u32 offset;
|
|
|
|
adjust_max_and_nice_len(&max_len, &nice_len,
|
|
in_end - in_next);
|
|
length = hc_matchfinder_longest_match(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next,
|
|
DEFLATE_MIN_MATCH_LEN - 1,
|
|
max_len,
|
|
nice_len,
|
|
c->max_search_depth,
|
|
next_hashes,
|
|
&offset);
|
|
|
|
if (length > DEFLATE_MIN_MATCH_LEN ||
|
|
(length == DEFLATE_MIN_MATCH_LEN &&
|
|
offset <= 4096)) {
|
|
/* Match found. */
|
|
deflate_choose_match(c, length, offset,
|
|
&litrunlen, &next_seq);
|
|
observe_match(&c->split_stats, length);
|
|
in_next = hc_matchfinder_skip_positions(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next + 1,
|
|
in_end,
|
|
length - 1,
|
|
next_hashes);
|
|
} else {
|
|
/* No match found. */
|
|
deflate_choose_literal(c, *in_next, &litrunlen);
|
|
observe_literal(&c->split_stats, *in_next);
|
|
in_next++;
|
|
}
|
|
|
|
/* Check if it's time to output another block. */
|
|
} while (in_next < in_max_block_end &&
|
|
!should_end_block(&c->split_stats,
|
|
in_block_begin, in_next, in_end));
|
|
|
|
deflate_finish_sequence(next_seq, litrunlen);
|
|
deflate_flush_block(c, &os, in_block_begin,
|
|
in_next - in_block_begin,
|
|
in_next == in_end, false);
|
|
} while (in_next != in_end);
|
|
|
|
return deflate_flush_output(&os);
|
|
}
|
|
|
|
static forceinline size_t
|
|
deflate_compress_lazy_generic(struct libdeflate_compressor * restrict c,
|
|
const u8 * restrict in, size_t in_nbytes,
|
|
u8 * restrict out, size_t out_nbytes_avail,
|
|
bool lazy2)
|
|
{
|
|
const u8 *in_next = in;
|
|
const u8 *in_end = in_next + in_nbytes;
|
|
struct deflate_output_bitstream os;
|
|
const u8 *in_cur_base = in_next;
|
|
unsigned max_len = DEFLATE_MAX_MATCH_LEN;
|
|
unsigned nice_len = MIN(c->nice_match_length, max_len);
|
|
u32 next_hashes[2] = {0, 0};
|
|
|
|
deflate_init_output(&os, out, out_nbytes_avail);
|
|
hc_matchfinder_init(&c->p.g.hc_mf);
|
|
|
|
do {
|
|
/* Starting a new DEFLATE block. */
|
|
|
|
const u8 * const in_block_begin = in_next;
|
|
const u8 * const in_max_block_end =
|
|
in_next + MIN(in_end - in_next, SOFT_MAX_BLOCK_LENGTH);
|
|
u32 litrunlen = 0;
|
|
struct deflate_sequence *next_seq = c->p.g.sequences;
|
|
|
|
init_block_split_stats(&c->split_stats);
|
|
deflate_reset_symbol_frequencies(c);
|
|
|
|
do {
|
|
unsigned cur_len;
|
|
unsigned cur_offset;
|
|
unsigned next_len;
|
|
unsigned next_offset;
|
|
|
|
/* Find the longest match at the current position. */
|
|
adjust_max_and_nice_len(&max_len, &nice_len,
|
|
in_end - in_next);
|
|
cur_len = hc_matchfinder_longest_match(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next,
|
|
DEFLATE_MIN_MATCH_LEN - 1,
|
|
max_len,
|
|
nice_len,
|
|
c->max_search_depth,
|
|
next_hashes,
|
|
&cur_offset);
|
|
if (cur_len < DEFLATE_MIN_MATCH_LEN ||
|
|
(cur_len == DEFLATE_MIN_MATCH_LEN &&
|
|
cur_offset > 8192)) {
|
|
/* No match found. Choose a literal. */
|
|
deflate_choose_literal(c, *in_next, &litrunlen);
|
|
observe_literal(&c->split_stats, *in_next);
|
|
in_next++;
|
|
continue;
|
|
}
|
|
in_next++;
|
|
|
|
have_cur_match:
|
|
observe_match(&c->split_stats, cur_len);
|
|
/*
|
|
* We have a match at the current position.
|
|
* If it's very long, choose it immediately.
|
|
*/
|
|
if (cur_len >= nice_len) {
|
|
deflate_choose_match(c, cur_len, cur_offset,
|
|
&litrunlen, &next_seq);
|
|
in_next = hc_matchfinder_skip_positions(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next,
|
|
in_end,
|
|
cur_len - 1,
|
|
next_hashes);
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* Try to find a better match at the next position.
|
|
*
|
|
* Note: since we already have a match at the *current*
|
|
* position, we use only half the 'max_search_depth'
|
|
* when checking the *next* position. This is a useful
|
|
* trade-off because it's more worthwhile to use a
|
|
* greater search depth on the initial match.
|
|
*
|
|
* Note: it's possible to structure the code such that
|
|
* there's only one call to longest_match(), which
|
|
* handles both the "find the initial match" and "try to
|
|
* find a better match" cases. However, it is faster to
|
|
* have two call sites, with longest_match() inlined at
|
|
* each.
|
|
*/
|
|
adjust_max_and_nice_len(&max_len, &nice_len,
|
|
in_end - in_next);
|
|
next_len = hc_matchfinder_longest_match(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next++,
|
|
cur_len - 1,
|
|
max_len,
|
|
nice_len,
|
|
c->max_search_depth >> 1,
|
|
next_hashes,
|
|
&next_offset);
|
|
if (next_len >= cur_len &&
|
|
4 * (int)(next_len - cur_len) +
|
|
((int)bsr32(cur_offset) -
|
|
(int)bsr32(next_offset)) > 2) {
|
|
/*
|
|
* Found a better match at the next position.
|
|
* Output a literal. Then the next match
|
|
* becomes the current match.
|
|
*/
|
|
deflate_choose_literal(c, *(in_next - 2),
|
|
&litrunlen);
|
|
cur_len = next_len;
|
|
cur_offset = next_offset;
|
|
goto have_cur_match;
|
|
}
|
|
|
|
if (lazy2) {
|
|
/* In lazy2 mode, look ahead another position */
|
|
adjust_max_and_nice_len(&max_len, &nice_len,
|
|
in_end - in_next);
|
|
next_len = hc_matchfinder_longest_match(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next++,
|
|
cur_len - 1,
|
|
max_len,
|
|
nice_len,
|
|
c->max_search_depth >> 2,
|
|
next_hashes,
|
|
&next_offset);
|
|
if (next_len >= cur_len &&
|
|
4 * (int)(next_len - cur_len) +
|
|
((int)bsr32(cur_offset) -
|
|
(int)bsr32(next_offset)) > 6) {
|
|
/*
|
|
* There's a much better match two
|
|
* positions ahead, so use two literals.
|
|
*/
|
|
deflate_choose_literal(
|
|
c, *(in_next - 3), &litrunlen);
|
|
deflate_choose_literal(
|
|
c, *(in_next - 2), &litrunlen);
|
|
cur_len = next_len;
|
|
cur_offset = next_offset;
|
|
goto have_cur_match;
|
|
}
|
|
/*
|
|
* No better match at either of the next 2
|
|
* positions. Output the current match.
|
|
*/
|
|
deflate_choose_match(c, cur_len, cur_offset,
|
|
&litrunlen, &next_seq);
|
|
if (cur_len > 3)
|
|
in_next = hc_matchfinder_skip_positions(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next,
|
|
in_end,
|
|
cur_len - 3,
|
|
next_hashes);
|
|
} else { /* !lazy2 */
|
|
/*
|
|
* No better match at the next position. Output
|
|
* the current match.
|
|
*/
|
|
deflate_choose_match(c, cur_len, cur_offset,
|
|
&litrunlen, &next_seq);
|
|
in_next = hc_matchfinder_skip_positions(
|
|
&c->p.g.hc_mf,
|
|
&in_cur_base,
|
|
in_next,
|
|
in_end,
|
|
cur_len - 2,
|
|
next_hashes);
|
|
}
|
|
/* Check if it's time to output another block. */
|
|
} while (in_next < in_max_block_end &&
|
|
!should_end_block(&c->split_stats,
|
|
in_block_begin, in_next, in_end));
|
|
|
|
deflate_finish_sequence(next_seq, litrunlen);
|
|
deflate_flush_block(c, &os, in_block_begin,
|
|
in_next - in_block_begin,
|
|
in_next == in_end, false);
|
|
} while (in_next != in_end);
|
|
|
|
return deflate_flush_output(&os);
|
|
}
|
|
|
|
/*
|
|
* This is the "lazy" DEFLATE compressor. Before choosing a match, it checks to
|
|
* see if there's a better match at the next position. If yes, it outputs a
|
|
* literal and continues to the next position. If no, it outputs the match.
|
|
*/
|
|
static size_t
|
|
deflate_compress_lazy(struct libdeflate_compressor * restrict c,
|
|
const u8 * restrict in, size_t in_nbytes,
|
|
u8 * restrict out, size_t out_nbytes_avail)
|
|
{
|
|
return deflate_compress_lazy_generic(c, in, in_nbytes, out,
|
|
out_nbytes_avail, false);
|
|
}
|
|
|
|
/*
|
|
* The lazy2 compressor. This is similar to the regular lazy one, but it looks
|
|
* for a better match at the next 2 positions rather than the next 1. This
|
|
* makes it take slightly more time, but compress some inputs slightly more.
|
|
*/
|
|
static size_t
|
|
deflate_compress_lazy2(struct libdeflate_compressor * restrict c,
|
|
const u8 * restrict in, size_t in_nbytes,
|
|
u8 * restrict out, size_t out_nbytes_avail)
|
|
{
|
|
return deflate_compress_lazy_generic(c, in, in_nbytes, out,
|
|
out_nbytes_avail, true);
|
|
}
|
|
|
|
#if SUPPORT_NEAR_OPTIMAL_PARSING
|
|
|
|
/*
|
|
* Follow the minimum-cost path in the graph of possible match/literal choices
|
|
* for the current block and compute the frequencies of the Huffman symbols that
|
|
* would be needed to output those matches and literals.
|
|
*/
|
|
static void
|
|
deflate_tally_item_list(struct libdeflate_compressor *c, u32 block_length)
|
|
{
|
|
struct deflate_optimum_node *cur_node = &c->p.n.optimum_nodes[0];
|
|
struct deflate_optimum_node *end_node = &c->p.n.optimum_nodes[block_length];
|
|
do {
|
|
unsigned length = cur_node->item & OPTIMUM_LEN_MASK;
|
|
unsigned offset = cur_node->item >> OPTIMUM_OFFSET_SHIFT;
|
|
|
|
if (length == 1) {
|
|
/* Literal */
|
|
c->freqs.litlen[offset]++;
|
|
} else {
|
|
/* Match */
|
|
c->freqs.litlen[DEFLATE_FIRST_LEN_SYM +
|
|
deflate_length_slot[length]]++;
|
|
c->freqs.offset[deflate_get_offset_slot(c, offset)]++;
|
|
}
|
|
cur_node += length;
|
|
} while (cur_node != end_node);
|
|
}
|
|
|
|
/* Set the current cost model from the codeword lengths specified in @lens. */
|
|
static void
|
|
deflate_set_costs_from_codes(struct libdeflate_compressor *c,
|
|
const struct deflate_lens *lens)
|
|
{
|
|
unsigned i;
|
|
|
|
/* Literals */
|
|
for (i = 0; i < DEFLATE_NUM_LITERALS; i++) {
|
|
u32 bits = (lens->litlen[i] ? lens->litlen[i] : LITERAL_NOSTAT_BITS);
|
|
c->p.n.costs.literal[i] = bits * BIT_COST;
|
|
}
|
|
|
|
/* Lengths */
|
|
for (i = DEFLATE_MIN_MATCH_LEN; i <= DEFLATE_MAX_MATCH_LEN; i++) {
|
|
unsigned length_slot = deflate_length_slot[i];
|
|
unsigned litlen_sym = DEFLATE_FIRST_LEN_SYM + length_slot;
|
|
u32 bits = (lens->litlen[litlen_sym] ? lens->litlen[litlen_sym] : LENGTH_NOSTAT_BITS);
|
|
bits += deflate_extra_length_bits[length_slot];
|
|
c->p.n.costs.length[i] = bits * BIT_COST;
|
|
}
|
|
|
|
/* Offset slots */
|
|
for (i = 0; i < ARRAY_LEN(deflate_offset_slot_base); i++) {
|
|
u32 bits = (lens->offset[i] ? lens->offset[i] : OFFSET_NOSTAT_BITS);
|
|
bits += deflate_extra_offset_bits[i];
|
|
c->p.n.costs.offset_slot[i] = bits * BIT_COST;
|
|
}
|
|
}
|
|
|
|
static forceinline u32
|
|
deflate_default_literal_cost(unsigned literal)
|
|
{
|
|
STATIC_ASSERT(BIT_COST == 8);
|
|
/* 66 is 8.25 bits/symbol */
|
|
return 66;
|
|
}
|
|
|
|
static forceinline u32
|
|
deflate_default_length_slot_cost(unsigned length_slot)
|
|
{
|
|
STATIC_ASSERT(BIT_COST == 8);
|
|
/* 60 is 7.5 bits/symbol */
|
|
return 60 + ((u32)deflate_extra_length_bits[length_slot] * BIT_COST);
|
|
}
|
|
|
|
static forceinline u32
|
|
deflate_default_offset_slot_cost(unsigned offset_slot)
|
|
{
|
|
STATIC_ASSERT(BIT_COST == 8);
|
|
/* 39 is 4.875 bits/symbol */
|
|
return 39 + ((u32)deflate_extra_offset_bits[offset_slot] * BIT_COST);
|
|
}
|
|
|
|
/*
|
|
* Set default symbol costs for the first block's first optimization pass.
|
|
*
|
|
* It works well to assume that each symbol is equally probable. This results
|
|
* in each symbol being assigned a cost of (-log2(1.0/num_syms) * BIT_COST)
|
|
* where 'num_syms' is the number of symbols in the corresponding alphabet.
|
|
* However, we intentionally bias the parse towards matches rather than literals
|
|
* by using a slightly lower default cost for length symbols than for literals.
|
|
* This often improves the compression ratio slightly.
|
|
*/
|
|
static void
|
|
deflate_set_default_costs(struct libdeflate_compressor *c)
|
|
{
|
|
unsigned i;
|
|
|
|
/* Literals */
|
|
for (i = 0; i < DEFLATE_NUM_LITERALS; i++)
|
|
c->p.n.costs.literal[i] = deflate_default_literal_cost(i);
|
|
|
|
/* Lengths */
|
|
for (i = DEFLATE_MIN_MATCH_LEN; i <= DEFLATE_MAX_MATCH_LEN; i++)
|
|
c->p.n.costs.length[i] = deflate_default_length_slot_cost(
|
|
deflate_length_slot[i]);
|
|
|
|
/* Offset slots */
|
|
for (i = 0; i < ARRAY_LEN(deflate_offset_slot_base); i++)
|
|
c->p.n.costs.offset_slot[i] = deflate_default_offset_slot_cost(i);
|
|
}
|
|
|
|
static forceinline void
|
|
deflate_adjust_cost(u32 *cost_p, u32 default_cost)
|
|
{
|
|
*cost_p += ((s32)default_cost - (s32)*cost_p) >> 1;
|
|
}
|
|
|
|
/*
|
|
* Adjust the costs when beginning a new block.
|
|
*
|
|
* Since the current costs have been optimized for the data, it's undesirable to
|
|
* throw them away and start over with the default costs. At the same time, we
|
|
* don't want to bias the parse by assuming that the next block will be similar
|
|
* to the current block. As a compromise, make the costs closer to the
|
|
* defaults, but don't simply set them to the defaults.
|
|
*/
|
|
static void
|
|
deflate_adjust_costs(struct libdeflate_compressor *c)
|
|
{
|
|
unsigned i;
|
|
|
|
/* Literals */
|
|
for (i = 0; i < DEFLATE_NUM_LITERALS; i++)
|
|
deflate_adjust_cost(&c->p.n.costs.literal[i],
|
|
deflate_default_literal_cost(i));
|
|
|
|
/* Lengths */
|
|
for (i = DEFLATE_MIN_MATCH_LEN; i <= DEFLATE_MAX_MATCH_LEN; i++)
|
|
deflate_adjust_cost(&c->p.n.costs.length[i],
|
|
deflate_default_length_slot_cost(
|
|
deflate_length_slot[i]));
|
|
|
|
/* Offset slots */
|
|
for (i = 0; i < ARRAY_LEN(deflate_offset_slot_base); i++)
|
|
deflate_adjust_cost(&c->p.n.costs.offset_slot[i],
|
|
deflate_default_offset_slot_cost(i));
|
|
}
|
|
|
|
/*
|
|
* Find the minimum-cost path through the graph of possible match/literal
|
|
* choices for this block.
|
|
*
|
|
* We find the minimum cost path from 'c->p.n.optimum_nodes[0]', which
|
|
* represents the node at the beginning of the block, to
|
|
* 'c->p.n.optimum_nodes[block_length]', which represents the node at the end of
|
|
* the block. Edge costs are evaluated using the cost model 'c->p.n.costs'.
|
|
*
|
|
* The algorithm works backwards, starting at the end node and proceeding
|
|
* backwards one node at a time. At each node, the minimum cost to reach the
|
|
* end node is computed and the match/literal choice that begins that path is
|
|
* saved.
|
|
*/
|
|
static void
|
|
deflate_find_min_cost_path(struct libdeflate_compressor *c,
|
|
const u32 block_length,
|
|
const struct lz_match *cache_ptr)
|
|
{
|
|
struct deflate_optimum_node *end_node = &c->p.n.optimum_nodes[block_length];
|
|
struct deflate_optimum_node *cur_node = end_node;
|
|
|
|
cur_node->cost_to_end = 0;
|
|
do {
|
|
unsigned num_matches;
|
|
unsigned literal;
|
|
u32 best_cost_to_end;
|
|
|
|
cur_node--;
|
|
cache_ptr--;
|
|
|
|
num_matches = cache_ptr->length;
|
|
literal = cache_ptr->offset;
|
|
|
|
/* It's always possible to choose a literal. */
|
|
best_cost_to_end = c->p.n.costs.literal[literal] +
|
|
(cur_node + 1)->cost_to_end;
|
|
cur_node->item = ((u32)literal << OPTIMUM_OFFSET_SHIFT) | 1;
|
|
|
|
/* Also consider matches if there are any. */
|
|
if (num_matches) {
|
|
const struct lz_match *match;
|
|
unsigned len;
|
|
unsigned offset;
|
|
unsigned offset_slot;
|
|
u32 offset_cost;
|
|
u32 cost_to_end;
|
|
|
|
/*
|
|
* Consider each length from the minimum
|
|
* (DEFLATE_MIN_MATCH_LEN) to the length of the longest
|
|
* match found at this position. For each length, we
|
|
* consider only the smallest offset for which that
|
|
* length is available. Although this is not guaranteed
|
|
* to be optimal due to the possibility of a larger
|
|
* offset costing less than a smaller offset to code,
|
|
* this is a very useful heuristic.
|
|
*/
|
|
match = cache_ptr - num_matches;
|
|
len = DEFLATE_MIN_MATCH_LEN;
|
|
do {
|
|
offset = match->offset;
|
|
offset_slot = deflate_get_offset_slot(c, offset);
|
|
offset_cost = c->p.n.costs.offset_slot[offset_slot];
|
|
do {
|
|
cost_to_end = offset_cost +
|
|
c->p.n.costs.length[len] +
|
|
(cur_node + len)->cost_to_end;
|
|
if (cost_to_end < best_cost_to_end) {
|
|
best_cost_to_end = cost_to_end;
|
|
cur_node->item = ((u32)offset << OPTIMUM_OFFSET_SHIFT) | len;
|
|
}
|
|
} while (++len <= match->length);
|
|
} while (++match != cache_ptr);
|
|
cache_ptr -= num_matches;
|
|
}
|
|
cur_node->cost_to_end = best_cost_to_end;
|
|
} while (cur_node != &c->p.n.optimum_nodes[0]);
|
|
}
|
|
|
|
/*
|
|
* Choose the literal/match sequence to use for the current block. The basic
|
|
* algorithm finds a minimum-cost path through the block's graph of
|
|
* literal/match choices, given a cost model. However, the cost of each symbol
|
|
* is unknown until the Huffman codes have been built, but at the same time the
|
|
* Huffman codes depend on the frequencies of chosen symbols. Consequently,
|
|
* multiple passes must be used to try to approximate an optimal solution. The
|
|
* first pass uses default costs, mixed with the costs from the previous block
|
|
* if any. Later passes use the Huffman codeword lengths from the previous pass
|
|
* as the costs.
|
|
*/
|
|
static void
|
|
deflate_optimize_block(struct libdeflate_compressor *c, u32 block_length,
|
|
const struct lz_match *cache_ptr, bool is_first_block)
|
|
{
|
|
unsigned num_passes_remaining = c->p.n.num_optim_passes;
|
|
u32 i;
|
|
|
|
/* Force the block to really end at the desired length, even if some
|
|
* matches extend beyond it. */
|
|
for (i = block_length; i <= MIN(block_length - 1 + DEFLATE_MAX_MATCH_LEN,
|
|
ARRAY_LEN(c->p.n.optimum_nodes) - 1); i++)
|
|
c->p.n.optimum_nodes[i].cost_to_end = 0x80000000;
|
|
|
|
/* Set the initial costs. */
|
|
if (is_first_block)
|
|
deflate_set_default_costs(c);
|
|
else
|
|
deflate_adjust_costs(c);
|
|
|
|
for (;;) {
|
|
/* Find the minimum cost path for this pass. */
|
|
deflate_find_min_cost_path(c, block_length, cache_ptr);
|
|
|
|
/* Compute frequencies of the chosen symbols. */
|
|
deflate_reset_symbol_frequencies(c);
|
|
deflate_tally_item_list(c, block_length);
|
|
|
|
if (--num_passes_remaining == 0)
|
|
break;
|
|
|
|
/* At least one optimization pass remains; update the costs. */
|
|
deflate_make_huffman_codes(&c->freqs, &c->codes);
|
|
deflate_set_costs_from_codes(c, &c->codes.lens);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* This is the "near-optimal" DEFLATE compressor. It computes the optimal
|
|
* representation of each DEFLATE block using a minimum-cost path search over
|
|
* the graph of possible match/literal choices for that block, assuming a
|
|
* certain cost for each Huffman symbol.
|
|
*
|
|
* For several reasons, the end result is not guaranteed to be optimal:
|
|
*
|
|
* - Nonoptimal choice of blocks
|
|
* - Heuristic limitations on which matches are actually considered
|
|
* - Symbol costs are unknown until the symbols have already been chosen
|
|
* (so iterative optimization must be used)
|
|
*/
|
|
static size_t
|
|
deflate_compress_near_optimal(struct libdeflate_compressor * restrict c,
|
|
const u8 * restrict in, size_t in_nbytes,
|
|
u8 * restrict out, size_t out_nbytes_avail)
|
|
{
|
|
const u8 *in_next = in;
|
|
const u8 *in_end = in_next + in_nbytes;
|
|
struct deflate_output_bitstream os;
|
|
const u8 *in_cur_base = in_next;
|
|
const u8 *in_next_slide =
|
|
in_next + MIN(in_end - in_next, MATCHFINDER_WINDOW_SIZE);
|
|
unsigned max_len = DEFLATE_MAX_MATCH_LEN;
|
|
unsigned nice_len = MIN(c->nice_match_length, max_len);
|
|
u32 next_hashes[2] = {0, 0};
|
|
|
|
deflate_init_output(&os, out, out_nbytes_avail);
|
|
bt_matchfinder_init(&c->p.n.bt_mf);
|
|
|
|
do {
|
|
/* Starting a new DEFLATE block. */
|
|
|
|
struct lz_match *cache_ptr = c->p.n.match_cache;
|
|
const u8 * const in_block_begin = in_next;
|
|
const u8 * const in_max_block_end =
|
|
in_next + MIN(in_end - in_next, SOFT_MAX_BLOCK_LENGTH);
|
|
const u8 *next_observation = in_next;
|
|
|
|
init_block_split_stats(&c->split_stats);
|
|
|
|
/*
|
|
* Find matches until we decide to end the block. We end the
|
|
* block if any of the following is true:
|
|
*
|
|
* (1) Maximum block length has been reached
|
|
* (2) Match catch may overflow.
|
|
* (3) Block split heuristic says to split now.
|
|
*/
|
|
do {
|
|
struct lz_match *matches;
|
|
unsigned best_len;
|
|
size_t remaining = in_end - in_next;
|
|
|
|
/* Slide the window forward if needed. */
|
|
if (in_next == in_next_slide) {
|
|
bt_matchfinder_slide_window(&c->p.n.bt_mf);
|
|
in_cur_base = in_next;
|
|
in_next_slide = in_next +
|
|
MIN(remaining, MATCHFINDER_WINDOW_SIZE);
|
|
}
|
|
|
|
/*
|
|
* Find matches with the current position using the
|
|
* binary tree matchfinder and save them in
|
|
* 'match_cache'.
|
|
*
|
|
* Note: the binary tree matchfinder is more suited for
|
|
* optimal parsing than the hash chain matchfinder. The
|
|
* reasons for this include:
|
|
*
|
|
* - The binary tree matchfinder can find more matches
|
|
* in the same number of steps.
|
|
* - One of the major advantages of hash chains is that
|
|
* skipping positions (not searching for matches at
|
|
* them) is faster; however, with optimal parsing we
|
|
* search for matches at almost all positions, so this
|
|
* advantage of hash chains is negated.
|
|
*/
|
|
matches = cache_ptr;
|
|
best_len = 0;
|
|
adjust_max_and_nice_len(&max_len, &nice_len, remaining);
|
|
if (likely(max_len >= BT_MATCHFINDER_REQUIRED_NBYTES)) {
|
|
cache_ptr = bt_matchfinder_get_matches(
|
|
&c->p.n.bt_mf,
|
|
in_cur_base,
|
|
in_next - in_cur_base,
|
|
max_len,
|
|
nice_len,
|
|
c->max_search_depth,
|
|
next_hashes,
|
|
&best_len,
|
|
matches);
|
|
}
|
|
|
|
if (in_next >= next_observation) {
|
|
if (best_len >= 4) {
|
|
observe_match(&c->split_stats,
|
|
best_len);
|
|
next_observation = in_next + best_len;
|
|
} else {
|
|
observe_literal(&c->split_stats,
|
|
*in_next);
|
|
next_observation = in_next + 1;
|
|
}
|
|
}
|
|
|
|
cache_ptr->length = cache_ptr - matches;
|
|
cache_ptr->offset = *in_next;
|
|
in_next++;
|
|
cache_ptr++;
|
|
|
|
/*
|
|
* If there was a very long match found, don't cache any
|
|
* matches for the bytes covered by that match. This
|
|
* avoids degenerate behavior when compressing highly
|
|
* redundant data, where the number of matches can be
|
|
* very large.
|
|
*
|
|
* This heuristic doesn't actually hurt the compression
|
|
* ratio very much. If there's a long match, then the
|
|
* data must be highly compressible, so it doesn't
|
|
* matter much what we do.
|
|
*/
|
|
if (best_len >= DEFLATE_MIN_MATCH_LEN &&
|
|
best_len >= nice_len) {
|
|
--best_len;
|
|
do {
|
|
remaining = in_end - in_next;
|
|
if (in_next == in_next_slide) {
|
|
bt_matchfinder_slide_window(
|
|
&c->p.n.bt_mf);
|
|
in_cur_base = in_next;
|
|
in_next_slide = in_next +
|
|
MIN(remaining,
|
|
MATCHFINDER_WINDOW_SIZE);
|
|
}
|
|
adjust_max_and_nice_len(&max_len,
|
|
&nice_len,
|
|
remaining);
|
|
if (max_len >=
|
|
BT_MATCHFINDER_REQUIRED_NBYTES) {
|
|
bt_matchfinder_skip_position(
|
|
&c->p.n.bt_mf,
|
|
in_cur_base,
|
|
in_next - in_cur_base,
|
|
nice_len,
|
|
c->max_search_depth,
|
|
next_hashes);
|
|
}
|
|
cache_ptr->length = 0;
|
|
cache_ptr->offset = *in_next;
|
|
in_next++;
|
|
cache_ptr++;
|
|
} while (--best_len);
|
|
}
|
|
} while (in_next < in_max_block_end &&
|
|
cache_ptr < &c->p.n.match_cache[CACHE_LENGTH] &&
|
|
!should_end_block(&c->split_stats,
|
|
in_block_begin, in_next, in_end));
|
|
/*
|
|
* All the matches for this block have been cached. Now choose
|
|
* the sequence of items to output and flush the block.
|
|
*/
|
|
deflate_optimize_block(c, in_next - in_block_begin, cache_ptr,
|
|
in_block_begin == in);
|
|
deflate_flush_block(c, &os, in_block_begin,
|
|
in_next - in_block_begin,
|
|
in_next == in_end, true);
|
|
} while (in_next != in_end);
|
|
|
|
return deflate_flush_output(&os);
|
|
}
|
|
|
|
#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
|
|
|
|
/* Initialize c->offset_slot_fast. */
|
|
static void
|
|
deflate_init_offset_slot_fast(struct libdeflate_compressor *c)
|
|
{
|
|
unsigned offset_slot;
|
|
unsigned offset;
|
|
unsigned offset_end;
|
|
|
|
for (offset_slot = 0;
|
|
offset_slot < ARRAY_LEN(deflate_offset_slot_base);
|
|
offset_slot++)
|
|
{
|
|
offset = deflate_offset_slot_base[offset_slot];
|
|
#if USE_FULL_OFFSET_SLOT_FAST
|
|
offset_end = offset + (1 << deflate_extra_offset_bits[offset_slot]);
|
|
do {
|
|
c->offset_slot_fast[offset] = offset_slot;
|
|
} while (++offset != offset_end);
|
|
#else
|
|
if (offset <= 256) {
|
|
offset_end = offset + (1 << deflate_extra_offset_bits[offset_slot]);
|
|
do {
|
|
c->offset_slot_fast[offset - 1] = offset_slot;
|
|
} while (++offset != offset_end);
|
|
} else {
|
|
offset_end = offset + (1 << deflate_extra_offset_bits[offset_slot]);
|
|
do {
|
|
c->offset_slot_fast[256 + ((offset - 1) >> 7)] = offset_slot;
|
|
} while ((offset += (1 << 7)) != offset_end);
|
|
}
|
|
#endif
|
|
}
|
|
}
|
|
|
|
LIBDEFLATEEXPORT struct libdeflate_compressor * LIBDEFLATEAPI
|
|
libdeflate_alloc_compressor(int compression_level)
|
|
{
|
|
struct libdeflate_compressor *c;
|
|
size_t size = offsetof(struct libdeflate_compressor, p);
|
|
|
|
if (compression_level < 0 || compression_level > 12)
|
|
return NULL;
|
|
|
|
#if SUPPORT_NEAR_OPTIMAL_PARSING
|
|
if (compression_level >= 10)
|
|
size += sizeof(c->p.n);
|
|
else if (compression_level >= 1)
|
|
size += sizeof(c->p.g);
|
|
#else
|
|
if (compression_level >= 1)
|
|
size += sizeof(c->p.g);
|
|
#endif
|
|
|
|
c = libdeflate_aligned_malloc(MATCHFINDER_MEM_ALIGNMENT, size);
|
|
if (!c)
|
|
return NULL;
|
|
|
|
c->compression_level = compression_level;
|
|
|
|
/*
|
|
* The higher the compression level, the more we should bother trying to
|
|
* compress very small inputs.
|
|
*/
|
|
c->min_size_to_compress = 56 - (compression_level * 4);
|
|
|
|
switch (compression_level) {
|
|
case 0:
|
|
c->impl = deflate_compress_none;
|
|
break;
|
|
case 1:
|
|
c->impl = deflate_compress_greedy;
|
|
c->max_search_depth = 2;
|
|
c->nice_match_length = 8;
|
|
break;
|
|
case 2:
|
|
c->impl = deflate_compress_greedy;
|
|
c->max_search_depth = 6;
|
|
c->nice_match_length = 10;
|
|
break;
|
|
case 3:
|
|
c->impl = deflate_compress_greedy;
|
|
c->max_search_depth = 12;
|
|
c->nice_match_length = 14;
|
|
break;
|
|
case 4:
|
|
c->impl = deflate_compress_greedy;
|
|
c->max_search_depth = 16;
|
|
c->nice_match_length = 30;
|
|
break;
|
|
case 5:
|
|
c->impl = deflate_compress_lazy;
|
|
c->max_search_depth = 16;
|
|
c->nice_match_length = 30;
|
|
break;
|
|
case 6:
|
|
c->impl = deflate_compress_lazy;
|
|
c->max_search_depth = 35;
|
|
c->nice_match_length = 65;
|
|
break;
|
|
case 7:
|
|
c->impl = deflate_compress_lazy;
|
|
c->max_search_depth = 100;
|
|
c->nice_match_length = 130;
|
|
break;
|
|
case 8:
|
|
c->impl = deflate_compress_lazy2;
|
|
c->max_search_depth = 300;
|
|
c->nice_match_length = DEFLATE_MAX_MATCH_LEN;
|
|
break;
|
|
case 9:
|
|
#if !SUPPORT_NEAR_OPTIMAL_PARSING
|
|
default:
|
|
#endif
|
|
c->impl = deflate_compress_lazy2;
|
|
c->max_search_depth = 600;
|
|
c->nice_match_length = DEFLATE_MAX_MATCH_LEN;
|
|
break;
|
|
#if SUPPORT_NEAR_OPTIMAL_PARSING
|
|
case 10:
|
|
c->impl = deflate_compress_near_optimal;
|
|
c->max_search_depth = 30;
|
|
c->nice_match_length = 50;
|
|
c->p.n.num_optim_passes = 2;
|
|
break;
|
|
case 11:
|
|
c->impl = deflate_compress_near_optimal;
|
|
c->max_search_depth = 60;
|
|
c->nice_match_length = 80;
|
|
c->p.n.num_optim_passes = 3;
|
|
break;
|
|
case 12:
|
|
default:
|
|
c->impl = deflate_compress_near_optimal;
|
|
c->max_search_depth = 100;
|
|
c->nice_match_length = 133;
|
|
c->p.n.num_optim_passes = 4;
|
|
break;
|
|
#endif /* SUPPORT_NEAR_OPTIMAL_PARSING */
|
|
}
|
|
|
|
deflate_init_offset_slot_fast(c);
|
|
deflate_init_static_codes(c);
|
|
|
|
return c;
|
|
}
|
|
|
|
LIBDEFLATEEXPORT size_t LIBDEFLATEAPI
|
|
libdeflate_deflate_compress(struct libdeflate_compressor *c,
|
|
const void *in, size_t in_nbytes,
|
|
void *out, size_t out_nbytes_avail)
|
|
{
|
|
if (unlikely(out_nbytes_avail < OUTPUT_END_PADDING))
|
|
return 0;
|
|
|
|
/* For extremely small inputs just use a single uncompressed block. */
|
|
if (unlikely(in_nbytes < c->min_size_to_compress)) {
|
|
struct deflate_output_bitstream os;
|
|
deflate_init_output(&os, out, out_nbytes_avail);
|
|
if (in_nbytes == 0)
|
|
in = &os; /* Avoid passing NULL to memcpy() */
|
|
deflate_write_uncompressed_block(&os, in, in_nbytes, true);
|
|
return deflate_flush_output(&os);
|
|
}
|
|
|
|
return (*c->impl)(c, in, in_nbytes, out, out_nbytes_avail);
|
|
}
|
|
|
|
LIBDEFLATEEXPORT void LIBDEFLATEAPI
|
|
libdeflate_free_compressor(struct libdeflate_compressor *c)
|
|
{
|
|
libdeflate_aligned_free(c);
|
|
}
|
|
|
|
unsigned int
|
|
deflate_get_compression_level(struct libdeflate_compressor *c)
|
|
{
|
|
return c->compression_level;
|
|
}
|
|
|
|
LIBDEFLATEEXPORT size_t LIBDEFLATEAPI
|
|
libdeflate_deflate_compress_bound(struct libdeflate_compressor *c,
|
|
size_t in_nbytes)
|
|
{
|
|
/*
|
|
* The worst case is all uncompressed blocks where one block has length
|
|
* <= MIN_BLOCK_LENGTH and the others have length MIN_BLOCK_LENGTH.
|
|
* Each uncompressed block has 5 bytes of overhead: 1 for BFINAL, BTYPE,
|
|
* and alignment to a byte boundary; 2 for LEN; and 2 for NLEN.
|
|
*/
|
|
size_t max_num_blocks = MAX(DIV_ROUND_UP(in_nbytes, MIN_BLOCK_LENGTH), 1);
|
|
return (5 * max_num_blocks) + in_nbytes + 1 + OUTPUT_END_PADDING;
|
|
}
|