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authorsnappy.mirrorbot@gmail.com <snappy.mirrorbot@gmail.com@03e5f5b5-db94-4691-08a0-1a8bf15f6143>2013-01-18 12:16:36 +0000
committersnappy.mirrorbot@gmail.com <snappy.mirrorbot@gmail.com@03e5f5b5-db94-4691-08a0-1a8bf15f6143>2013-01-18 12:16:36 +0000
commit63ad19f83c6a2a2e9c0bfffeff7fa79522f2ea0f (patch)
tree548baedea4a273fecc97a54d2eb8a671d664b5d6
parent2f74bc6e350a83e5568c961b9a6505ae2015aea9 (diff)
downloadsnappy-63ad19f83c6a2a2e9c0bfffeff7fa79522f2ea0f.tar.gz
Increase the Zippy block size from 32 kB to 64 kB, winning ~3% density
while being effectively performance neutral. The longer story about density is that we win 3-6% density on the benchmarks where this has any effect at all; many of the benchmarks (cp, c, lsp, man) are smaller than 32 kB and thus will have no effect. Binary data also seems to win little or nothing; of course, the already-compressed data wins nothing. The protobuf benchmark wins as much as ~18% depending on architecture, but I wouldn't be too sure that this is representative of protobuf data in general. As of performance, we lose a tiny amount since we get more tags (e.g., a long literal might be broken up into literal-copy-literal), but we win it back with less clearing of the hash table, and more opportunities to skip incompressible data (e.g. in the jpg benchmark). Decompression seems to get ever so slightly slower, again due to more tags. The total net change is about as close to zero as we can get, so the end effect seems to be simply more density and no real performance change. The comment about not changing kBlockSize, scary as it is, is not really relevant, since we're never going to have a block-level decompressor without explicitly marked blocks. Replace it with something more appropriate. This affects the framing format, but it's okay to change it since it basically has no users yet. Density (note that cp, c, lsp and man are all smaller than 32 kB): Benchmark Description Base (%) New (%) Improvement -------------------------------------------------------------- ZFlat/0 html 22.57 22.31 +5.6% ZFlat/1 urls 50.89 47.77 +6.5% ZFlat/2 jpg 99.88 99.87 +0.0% ZFlat/3 pdf 82.13 82.07 +0.1% ZFlat/4 html4 23.55 22.51 +4.6% ZFlat/5 cp 48.12 48.12 +0.0% ZFlat/6 c 42.40 42.40 +0.0% ZFlat/7 lsp 48.37 48.37 +0.0% ZFlat/8 xls 41.34 41.23 +0.3% ZFlat/9 txt1 59.81 57.87 +3.4% ZFlat/10 txt2 64.07 61.93 +3.5% ZFlat/11 txt3 57.11 54.92 +4.0% ZFlat/12 txt4 68.35 66.22 +3.2% ZFlat/13 bin 18.21 18.11 +0.6% ZFlat/14 sum 51.88 48.96 +6.0% ZFlat/15 man 59.36 59.36 +0.0% ZFlat/16 pb 23.15 19.64 +17.9% ZFlat/17 gaviota 38.27 37.72 +1.5% Geometric mean 45.51 44.15 +3.1% Microbenchmarks (64-bit, opt): Westmere 2.8 GHz: Benchmark Base (ns) New (ns) Improvement ------------------------------------------------------------------------------------------------- BM_UFlat/0 75342 75027 1.3GB/s html +0.4% BM_UFlat/1 723767 744269 899.6MB/s urls -2.8% BM_UFlat/2 10072 10072 11.7GB/s jpg +0.0% BM_UFlat/3 30747 30388 2.9GB/s pdf +1.2% BM_UFlat/4 307353 306063 1.2GB/s html4 +0.4% BM_UFlat/5 28593 28743 816.3MB/s cp -0.5% BM_UFlat/6 12958 12998 818.1MB/s c -0.3% BM_UFlat/7 3700 3792 935.8MB/s lsp -2.4% BM_UFlat/8 999685 999905 982.1MB/s xls -0.0% BM_UFlat/9 232954 230079 630.4MB/s txt1 +1.2% BM_UFlat/10 200785 201468 592.6MB/s txt2 -0.3% BM_UFlat/11 617267 610968 666.1MB/s txt3 +1.0% BM_UFlat/12 821595 822475 558.7MB/s txt4 -0.1% BM_UFlat/13 377097 377632 1.3GB/s bin -0.1% BM_UFlat/14 45476 45260 805.8MB/s sum +0.5% BM_UFlat/15 4985 5003 805.7MB/s man -0.4% BM_UFlat/16 80813 77494 1.4GB/s pb +4.3% BM_UFlat/17 251792 241553 727.7MB/s gaviota +4.2% BM_UValidate/0 40343 40354 2.4GB/s html -0.0% BM_UValidate/1 426890 451574 1.4GB/s urls -5.5% BM_UValidate/2 187 179 661.9GB/s jpg +4.5% BM_UValidate/3 13783 13827 6.4GB/s pdf -0.3% BM_UValidate/4 162393 163335 2.3GB/s html4 -0.6% BM_UDataBuffer/0 93756 93302 1046.7MB/s html +0.5% BM_UDataBuffer/1 886714 916292 730.7MB/s urls -3.2% BM_UDataBuffer/2 15861 16401 7.2GB/s jpg -3.3% BM_UDataBuffer/3 38934 39224 2.2GB/s pdf -0.7% BM_UDataBuffer/4 381008 379428 1029.5MB/s html4 +0.4% BM_UCord/0 92528 91098 1072.0MB/s html +1.6% BM_UCord/1 858421 885287 756.3MB/s urls -3.0% BM_UCord/2 13140 13464 8.8GB/s jpg -2.4% BM_UCord/3 39012 37773 2.3GB/s pdf +3.3% BM_UCord/4 376869 371267 1052.1MB/s html4 +1.5% BM_UCordString/0 75810 75303 1.3GB/s html +0.7% BM_UCordString/1 735290 753841 888.2MB/s urls -2.5% BM_UCordString/2 11945 13113 9.0GB/s jpg -8.9% BM_UCordString/3 33901 32562 2.7GB/s pdf +4.1% BM_UCordString/4 310985 309390 1.2GB/s html4 +0.5% BM_UCordValidate/0 40952 40450 2.4GB/s html +1.2% BM_UCordValidate/1 433842 456531 1.4GB/s urls -5.0% BM_UCordValidate/2 1179 1173 100.8GB/s jpg +0.5% BM_UCordValidate/3 14481 14392 6.1GB/s pdf +0.6% BM_UCordValidate/4 164364 164151 2.3GB/s html4 +0.1% BM_ZFlat/0 160610 156601 623.6MB/s html (22.31 %) +2.6% BM_ZFlat/1 1995238 1993582 335.9MB/s urls (47.77 %) +0.1% BM_ZFlat/2 30133 24983 4.7GB/s jpg (99.87 %) +20.6% BM_ZFlat/3 74453 73128 1.2GB/s pdf (82.07 %) +1.8% BM_ZFlat/4 647674 633729 616.4MB/s html4 (22.51 %) +2.2% BM_ZFlat/5 76259 76090 308.4MB/s cp (48.12 %) +0.2% BM_ZFlat/6 31106 31084 342.1MB/s c (42.40 %) +0.1% BM_ZFlat/7 10507 10443 339.8MB/s lsp (48.37 %) +0.6% BM_ZFlat/8 1811047 1793325 547.6MB/s xls (41.23 %) +1.0% BM_ZFlat/9 597903 581793 249.3MB/s txt1 (57.87 %) +2.8% BM_ZFlat/10 525320 514522 232.0MB/s txt2 (61.93 %) +2.1% BM_ZFlat/11 1596591 1551636 262.3MB/s txt3 (54.92 %) +2.9% BM_ZFlat/12 2134523 2094033 219.5MB/s txt4 (66.22 %) +1.9% BM_ZFlat/13 593024 587869 832.6MB/s bin (18.11 %) +0.9% BM_ZFlat/14 114746 110666 329.5MB/s sum (48.96 %) +3.7% BM_ZFlat/15 14376 14485 278.3MB/s man (59.36 %) -0.8% BM_ZFlat/16 167908 150070 753.6MB/s pb (19.64 %) +11.9% BM_ZFlat/17 460228 442253 397.5MB/s gaviota (37.72 %) +4.1% BM_ZCord/0 164896 160241 609.4MB/s html +2.9% BM_ZCord/1 2070239 2043492 327.7MB/s urls +1.3% BM_ZCord/2 54402 47002 2.5GB/s jpg +15.7% BM_ZCord/3 85871 83832 1073.1MB/s pdf +2.4% BM_ZCord/4 664078 648825 602.0MB/s html4 +2.4% BM_ZDataBuffer/0 174874 172549 566.0MB/s html +1.3% BM_ZDataBuffer/1 2134410 2139173 313.0MB/s urls -0.2% BM_ZDataBuffer/2 71911 69551 1.7GB/s jpg +3.4% BM_ZDataBuffer/3 98236 99727 902.1MB/s pdf -1.5% BM_ZDataBuffer/4 710776 699104 558.8MB/s html4 +1.7% Sum of all benchmarks 27358908 27200688 +0.6% Sandy Bridge 2.6 GHz: Benchmark Base (ns) New (ns) Improvement ------------------------------------------------------------------------------------------------- BM_UFlat/0 49356 49018 1.9GB/s html +0.7% BM_UFlat/1 516764 531955 1.2GB/s urls -2.9% BM_UFlat/2 6982 7304 16.2GB/s jpg -4.4% BM_UFlat/3 15285 15598 5.6GB/s pdf -2.0% BM_UFlat/4 206557 206669 1.8GB/s html4 -0.1% BM_UFlat/5 13681 13567 1.7GB/s cp +0.8% BM_UFlat/6 6571 6592 1.6GB/s c -0.3% BM_UFlat/7 2008 1994 1.7GB/s lsp +0.7% BM_UFlat/8 775700 773286 1.2GB/s xls +0.3% BM_UFlat/9 165578 164480 881.8MB/s txt1 +0.7% BM_UFlat/10 143707 144139 828.2MB/s txt2 -0.3% BM_UFlat/11 443026 436281 932.8MB/s txt3 +1.5% BM_UFlat/12 603129 595856 771.2MB/s txt4 +1.2% BM_UFlat/13 271682 270450 1.8GB/s bin +0.5% BM_UFlat/14 26200 25666 1.4GB/s sum +2.1% BM_UFlat/15 2620 2608 1.5GB/s man +0.5% BM_UFlat/16 48908 47756 2.3GB/s pb +2.4% BM_UFlat/17 174638 170346 1031.9MB/s gaviota +2.5% BM_UValidate/0 31922 31898 3.0GB/s html +0.1% BM_UValidate/1 341265 363554 1.8GB/s urls -6.1% BM_UValidate/2 160 151 782.8GB/s jpg +6.0% BM_UValidate/3 10402 10380 8.5GB/s pdf +0.2% BM_UValidate/4 129490 130587 2.9GB/s html4 -0.8% BM_UDataBuffer/0 59383 58736 1.6GB/s html +1.1% BM_UDataBuffer/1 619222 637786 1049.8MB/s urls -2.9% BM_UDataBuffer/2 10775 11941 9.9GB/s jpg -9.8% BM_UDataBuffer/3 18002 17930 4.9GB/s pdf +0.4% BM_UDataBuffer/4 259182 259306 1.5GB/s html4 -0.0% BM_UCord/0 59379 57814 1.6GB/s html +2.7% BM_UCord/1 598456 615162 1088.4MB/s urls -2.7% BM_UCord/2 8519 8628 13.7GB/s jpg -1.3% BM_UCord/3 18123 17537 5.0GB/s pdf +3.3% BM_UCord/4 252375 252331 1.5GB/s html4 +0.0% BM_UCordString/0 49494 49790 1.9GB/s html -0.6% BM_UCordString/1 524659 541803 1.2GB/s urls -3.2% BM_UCordString/2 8206 8354 14.2GB/s jpg -1.8% BM_UCordString/3 17235 16537 5.3GB/s pdf +4.2% BM_UCordString/4 210188 211072 1.8GB/s html4 -0.4% BM_UCordValidate/0 31956 31587 3.0GB/s html +1.2% BM_UCordValidate/1 340828 362141 1.8GB/s urls -5.9% BM_UCordValidate/2 783 744 158.9GB/s jpg +5.2% BM_UCordValidate/3 10543 10462 8.4GB/s pdf +0.8% BM_UCordValidate/4 130150 129789 2.9GB/s html4 +0.3% BM_ZFlat/0 113873 111200 878.2MB/s html (22.31 %) +2.4% BM_ZFlat/1 1473023 1489858 449.4MB/s urls (47.77 %) -1.1% BM_ZFlat/2 23569 19486 6.1GB/s jpg (99.87 %) +21.0% BM_ZFlat/3 49178 48046 1.8GB/s pdf (82.07 %) +2.4% BM_ZFlat/4 475063 469394 832.2MB/s html4 (22.51 %) +1.2% BM_ZFlat/5 46910 46816 501.2MB/s cp (48.12 %) +0.2% BM_ZFlat/6 16883 16916 628.6MB/s c (42.40 %) -0.2% BM_ZFlat/7 5381 5447 651.5MB/s lsp (48.37 %) -1.2% BM_ZFlat/8 1466870 1473861 666.3MB/s xls (41.23 %) -0.5% BM_ZFlat/9 468006 464101 312.5MB/s txt1 (57.87 %) +0.8% BM_ZFlat/10 408157 408957 291.9MB/s txt2 (61.93 %) -0.2% BM_ZFlat/11 1253348 1232910 330.1MB/s txt3 (54.92 %) +1.7% BM_ZFlat/12 1702373 1702977 269.8MB/s txt4 (66.22 %) -0.0% BM_ZFlat/13 439792 438557 1116.0MB/s bin (18.11 %) +0.3% BM_ZFlat/14 80766 78851 462.5MB/s sum (48.96 %) +2.4% BM_ZFlat/15 7420 7542 534.5MB/s man (59.36 %) -1.6% BM_ZFlat/16 112043 100126 1.1GB/s pb (19.64 %) +11.9% BM_ZFlat/17 368877 357703 491.4MB/s gaviota (37.72 %) +3.1% BM_ZCord/0 116402 113564 859.9MB/s html +2.5% BM_ZCord/1 1507156 1519911 440.5MB/s urls -0.8% BM_ZCord/2 39860 33686 3.5GB/s jpg +18.3% BM_ZCord/3 56211 54694 1.6GB/s pdf +2.8% BM_ZCord/4 485594 479212 815.1MB/s html4 +1.3% BM_ZDataBuffer/0 123185 121572 803.3MB/s html +1.3% BM_ZDataBuffer/1 1569111 1589380 421.3MB/s urls -1.3% BM_ZDataBuffer/2 53143 49556 2.4GB/s jpg +7.2% BM_ZDataBuffer/3 65725 66826 1.3GB/s pdf -1.6% BM_ZDataBuffer/4 517871 514750 758.9MB/s html4 +0.6% Sum of all benchmarks 20258879 20315484 -0.3% AMD Instanbul 2.4 GHz: Benchmark Base (ns) New (ns) Improvement ------------------------------------------------------------------------------------------------- BM_UFlat/0 97120 96585 1011.1MB/s html +0.6% BM_UFlat/1 917473 948016 706.3MB/s urls -3.2% BM_UFlat/2 21496 23938 4.9GB/s jpg -10.2% BM_UFlat/3 44751 45639 1.9GB/s pdf -1.9% BM_UFlat/4 391950 391413 998.0MB/s html4 +0.1% BM_UFlat/5 37366 37201 630.7MB/s cp +0.4% BM_UFlat/6 18350 18318 580.5MB/s c +0.2% BM_UFlat/7 5672 5661 626.9MB/s lsp +0.2% BM_UFlat/8 1533390 1529441 642.1MB/s xls +0.3% BM_UFlat/9 335477 336553 431.0MB/s txt1 -0.3% BM_UFlat/10 285140 292080 408.7MB/s txt2 -2.4% BM_UFlat/11 888507 894758 454.9MB/s txt3 -0.7% BM_UFlat/12 1187643 1210928 379.5MB/s txt4 -1.9% BM_UFlat/13 493717 507447 964.5MB/s bin -2.7% BM_UFlat/14 61740 60870 599.1MB/s sum +1.4% BM_UFlat/15 7211 7187 560.9MB/s man +0.3% BM_UFlat/16 97435 93100 1.2GB/s pb +4.7% BM_UFlat/17 362662 356395 493.2MB/s gaviota +1.8% BM_UValidate/0 47475 47118 2.0GB/s html +0.8% BM_UValidate/1 501304 529741 1.2GB/s urls -5.4% BM_UValidate/2 276 243 486.2GB/s jpg +13.6% BM_UValidate/3 16361 16261 5.4GB/s pdf +0.6% BM_UValidate/4 190741 190353 2.0GB/s html4 +0.2% BM_UDataBuffer/0 111080 109771 889.6MB/s html +1.2% BM_UDataBuffer/1 1051035 1085999 616.5MB/s urls -3.2% BM_UDataBuffer/2 25801 25463 4.6GB/s jpg +1.3% BM_UDataBuffer/3 50493 49946 1.8GB/s pdf +1.1% BM_UDataBuffer/4 447258 444138 879.5MB/s html4 +0.7% BM_UCord/0 109350 107909 905.0MB/s html +1.3% BM_UCord/1 1023396 1054964 634.7MB/s urls -3.0% BM_UCord/2 25292 24371 4.9GB/s jpg +3.8% BM_UCord/3 48955 49736 1.8GB/s pdf -1.6% BM_UCord/4 440452 437331 893.2MB/s html4 +0.7% BM_UCordString/0 98511 98031 996.2MB/s html +0.5% BM_UCordString/1 933230 963495 694.9MB/s urls -3.1% BM_UCordString/2 23311 24076 4.9GB/s jpg -3.2% BM_UCordString/3 45568 46196 1.9GB/s pdf -1.4% BM_UCordString/4 397791 396934 984.1MB/s html4 +0.2% BM_UCordValidate/0 47537 46921 2.0GB/s html +1.3% BM_UCordValidate/1 505071 532716 1.2GB/s urls -5.2% BM_UCordValidate/2 1663 1621 72.9GB/s jpg +2.6% BM_UCordValidate/3 16890 16926 5.2GB/s pdf -0.2% BM_UCordValidate/4 192365 191984 2.0GB/s html4 +0.2% BM_ZFlat/0 184708 179103 545.3MB/s html (22.31 %) +3.1% BM_ZFlat/1 2293864 2302950 290.7MB/s urls (47.77 %) -0.4% BM_ZFlat/2 52852 47618 2.5GB/s jpg (99.87 %) +11.0% BM_ZFlat/3 100766 96179 935.3MB/s pdf (82.07 %) +4.8% BM_ZFlat/4 741220 727977 536.6MB/s html4 (22.51 %) +1.8% BM_ZFlat/5 85402 85418 274.7MB/s cp (48.12 %) -0.0% BM_ZFlat/6 36558 36494 291.4MB/s c (42.40 %) +0.2% BM_ZFlat/7 12706 12507 283.7MB/s lsp (48.37 %) +1.6% BM_ZFlat/8 2336823 2335688 420.5MB/s xls (41.23 %) +0.0% BM_ZFlat/9 701804 681153 212.9MB/s txt1 (57.87 %) +3.0% BM_ZFlat/10 606700 597194 199.9MB/s txt2 (61.93 %) +1.6% BM_ZFlat/11 1852283 1803238 225.7MB/s txt3 (54.92 %) +2.7% BM_ZFlat/12 2475527 2443354 188.1MB/s txt4 (66.22 %) +1.3% BM_ZFlat/13 694497 696654 702.6MB/s bin (18.11 %) -0.3% BM_ZFlat/14 136929 129855 280.8MB/s sum (48.96 %) +5.4% BM_ZFlat/15 17172 17124 235.4MB/s man (59.36 %) +0.3% BM_ZFlat/16 190364 171763 658.4MB/s pb (19.64 %) +10.8% BM_ZFlat/17 567285 555190 316.6MB/s gaviota (37.72 %) +2.2% BM_ZCord/0 193490 187031 522.1MB/s html +3.5% BM_ZCord/1 2427537 2415315 277.2MB/s urls +0.5% BM_ZCord/2 85378 81412 1.5GB/s jpg +4.9% BM_ZCord/3 121898 119419 753.3MB/s pdf +2.1% BM_ZCord/4 779564 762961 512.0MB/s html4 +2.2% BM_ZDataBuffer/0 213820 207272 471.1MB/s html +3.2% BM_ZDataBuffer/1 2589010 2586495 258.9MB/s urls +0.1% BM_ZDataBuffer/2 121871 118885 1018.4MB/s jpg +2.5% BM_ZDataBuffer/3 145382 145986 616.2MB/s pdf -0.4% BM_ZDataBuffer/4 868117 852754 458.1MB/s html4 +1.8% Sum of all benchmarks 33771833 33744763 +0.1% git-svn-id: http://snappy.googlecode.com/svn/trunk@71 03e5f5b5-db94-4691-08a0-1a8bf15f6143
Diffstat
-rw-r--r--framing_format.txt18
-rw-r--r--snappy.h17
2 files changed, 18 insertions, 17 deletions
diff --git a/framing_format.txt b/framing_format.txt
index 08fda03..32b1e59 100644
--- a/framing_format.txt
+++ b/framing_format.txt
@@ -1,5 +1,5 @@
Snappy framing format description
-Last revised: 2011-12-15
+Last revised: 2013-01-05
This format decribes a framing format for Snappy, allowing compressing to
files or streams that can then more easily be decompressed without having
@@ -15,9 +15,9 @@ decompressor; it is not part of the Snappy core specification.
The file consists solely of chunks, lying back-to-back with no padding
in between. Each chunk consists first a single byte of chunk identifier,
-then a two-byte little-endian length of the chunk in bytes (from 0 to 65535,
-inclusive), and then the data if any. The three bytes of chunk header is not
-counted in the data length.
+then a three-byte little-endian length of the chunk in bytes (from 0 to
+16777215, inclusive), and then the data if any. The four bytes of chunk
+header is not counted in the data length.
The different chunk types are listed below. The first chunk must always
be the stream identifier chunk (see section 4.1, below). The stream
@@ -71,7 +71,7 @@ The stream identifier is always the first element in the stream.
It is exactly six bytes long and contains "sNaPpY" in ASCII. This means that
a valid Snappy framed stream always starts with the bytes
- 0xff 0x06 0x00 0x73 0x4e 0x61 0x50 0x70 0x59
+ 0xff 0x06 0x00 0x00 0x73 0x4e 0x61 0x50 0x70 0x59
The stream identifier chunk can come multiple times in the stream besides
the first; if such a chunk shows up, it should simply be ignored, assuming
@@ -86,9 +86,9 @@ see the compressed format specification. The compressed data is preceded by
the CRC-32C (see section 3) of the _uncompressed_ data.
Note that the data portion of the chunk, i.e., the compressed contents,
-can be at most 65531 bytes (2^16 - 1, minus the checksum).
+can be at most 16777211 bytes (2^24 - 1, minus the checksum).
However, we place an additional restriction that the uncompressed data
-in a chunk must be no longer than 32768 bytes. This allows consumers to
+in a chunk must be no longer than 65536 bytes. This allows consumers to
easily use small fixed-size buffers.
@@ -102,8 +102,8 @@ As in the compressed chunks, the data is preceded by its own masked
CRC-32C (see section 3).
An uncompressed data chunk, like compressed data chunks, should contain
-no more than 32768 data bytes, so the maximum legal chunk length with the
-checksum is 32772.
+no more than 65536 data bytes, so the maximum legal chunk length with the
+checksum is 65540.
4.4. Reserved unskippable chunks (chunk types 0x02-0x7f)
diff --git a/snappy.h b/snappy.h
index d15ffbf..03ef6ce 100644
--- a/snappy.h
+++ b/snappy.h
@@ -142,15 +142,16 @@ namespace snappy {
bool IsValidCompressedBuffer(const char* compressed,
size_t compressed_length);
- // *** DO NOT CHANGE THE VALUE OF kBlockSize ***
+ // The size of a compression block. Note that many parts of the compression
+ // code assumes that kBlockSize <= 65536; in particular, the hash table
+ // can only store 16-bit offsets, and EmitCopy() also assumes the offset
+ // is 65535 bytes or less. Note also that if you change this, it will
+ // affect the framing format (see framing_format.txt).
//
- // New Compression code chops up the input into blocks of at most
- // the following size. This ensures that back-references in the
- // output never cross kBlockSize block boundaries. This can be
- // helpful in implementing blocked decompression. However the
- // decompression code should not rely on this guarantee since older
- // compression code may not obey it.
- static const int kBlockLog = 15;
+ // Note that there might be older data around that is compressed with larger
+ // block sizes, so the decompression code should not rely on the
+ // non-existence of long backreferences.
+ static const int kBlockLog = 16;
static const size_t kBlockSize = 1 << kBlockLog;
static const int kMaxHashTableBits = 14;
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