LZMA Докладчик: Гареев Роман email: [email protected] LZMA (Lempel-Ziv-Markov chain-Algorithm) 7z(7-Zip) LZMA SDK 2/31 3/31 4/31 LZMA: LZ77(Sliding Window) Deflate: Zip and Gzip Range Encoding 5/31 LZ77 (Sliding Window) Jacob Ziv Abraham Lempel 6/31 In computer science and information theory, data compression, source coding, or bit-rate reduction involves encoding information using fewer bits than the original representation. Compression can be either lossy or lossless. Lossless compression reduces bits by identifying and eliminating statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by identifying marginally important information and removing it. Compression is useful because it helps reduce the consumption of resources such as data space or transmission capacity. Because compressed data must be decompressed to be used, this extra processing imposes computational or other costs through decompression. For instance, a compression scheme for video may require expensive hardware for the video to be decompressed fast enough to be viewed as it is being decompressed, and the option to decompress the video in full before watching it may be inconvenient or require additional storage. The design of data compression schemes involve trade-offs among various factors, including the degree of compression, the amount of distortion introduced (e.g., when using lossy data compression), and the computational resources required to compress and uncompress the data. 7/31 Закодированный текст… sir sid eastman easily t eases sea sick seals … Текст для … (16, 3, “e”) Закодированный текст… sir sid eastman easily tease s sea sick seals …. Текст для … sir sid eastman ⇒ (0,0,“s”) s ir sid eastman e ⇒ (0,0,“i”) si r sid eastman ea ⇒ (0,0,“r”) sir sid eastman eas ⇒ (0,0,“ ”) sir sid eastman easi ⇒ (4,2,“d”) 8/31 Huffman Coding a1 0.4 a2 0.2 a3 0.2 a4 0.1 a5 0.1 0.4 0.2 a2 0.2 a3 0.1 0 a1 a4 a12345 0 a2345 1 a345 1 a5 0 1 0.6 0.4 0 a45 0.1 1 1.0 0.2 9/31 Deflate: Zip and Gzip Phillip Katz 10 /31 (сдвиг, длина, символ) ⇒ (сдвиг, длина) Закодированный текст… old ...she needs..then…there… the new... Текст для пр… Режимы: Normal High-compression Fast Режимы сжатия: •Без сжатия •Сжатие с фиксированным размером таблиц •Сжатие с индивидуальными таблицами, создаваемыми для текущей информации 11 /31 “range encoding” “Handbook of Data Compression” David Salomon, Giovanni Motta 12 /31 LZMA Закодированный текст… … the new... Текст для пр… индекс bt2 Binary Tree with 2 bytes hashing bt3 Binary Tree with 3 bytes hashing bt4 Binary Tree with 4 bytes hashing hc4 Hash Chain with 4 bytes hashing “hash-chain”, “binary-tree” 13 /31 Hash-chain XY … 123 … 123 … … … 24 … … 14/31 Binary-tree …abm…abcd2…abcx…abcd1…aby… 11 24 30 57 78 62 62 11 24 abm… 62 abcd2… 11 abm… 30 24 abcd2… 62 abcx… 57 11 abm… 62 abcd1… 30 24 abcd2… abcx… 11 abm… aby… 78 abcd1… 57 30 24 abcx… 11 abm… 15 /31 Пример реализации LZMA(реализация на JAVA из LZMA SDK) 16 /31 LZMA SDK 2004 ANSI-C/C++/C#/Java lzma.exe lzma.txt 7zFormat.txt history.txt 17 /31 Основные характеристики LZMA SDK Различный размер словаря Предполагаемая скорость сжатия: около 2MB/s на 2 GHz CPU Предполагаемая скорость распаковки: 20-30 MB/s на 2 GHz Core 2 или AMD Athlon 64 1-2 MB/s на 200 MHz RISC Небольшое количество затрат памяти для распаковки(16 KB + размер словаря) Поддержка многопоточности 18 /31 Основные опции LZMA SDK a{N} Режим сжатия. 0, 1, 2 fast, normal, max -d{N} -si -so -mf{MF_ID} MF_ID bt2 bt3 bt4 hc4 Memory d * 9.5 + 4MB d * 11.5 + 4MB d * 11.5 + 4MB d * 7.5 + 4MB Description Binary Tree с 2 байтным хэшированием Binary Tree с 3 байтным хэшированием Binary Tree с 4 байтным хэшированием Hash Chain с 4 байтным хэшированием 19 /31 Lasse Collin http://tukaani.org 20 /31 Сравнение Gzip, Bzip2 и LZMA AMD mobile Athlon XP2400+ 512 MB RAM Linux 2.6.12 gzip 1.3.3, bzip2 1.0.3, LZMA SDK 4.17 (lzmash) Обращалось внимание на: размер файлов после сжатия время распаковки память, требуемая для распаковки обычный формат, который все знают 21 /31 Tar archive OpenOffice.org 1.1.4(Linux) (203 MB) Compressed size / Uncompressed size * 100% gzip bzip2 lzmash 1 40,6% 35,8% 31,7% 2 39,9% 34,9% 29,2% 3 39,3% 34,5% 28,0% 4 38,2% 34,3% 27,4% 5 37,5% 34,2% 26,7% 6 37,2% 34,1% 26,4% 7 37,1% 34,1% 26,1% 8 37,1% 34,0% 25,7% 9 37,0% 34,0% 25,4% 22 /31 Tar archive OpenOffice.org 1.1.4(Linux) (203 MB) Compression time Decompression time gzip bzip2 lzmash gzip bzip2 lzmash 1 11.5s 1m 26s 0m 58s 1 3.3s 16.5s 11.3s 2 12.0s 1m 40s 2m 7s 2 3.3s 24.2s 10.5s 3 13.7s 1m 54s 4m 58s 3 3.3s 29.2s 10.5s 4 15.1s 2m 5s 5m 26s 4 3.3s 32.1s 10.4s 5 18.4s 2m 11s 6m 47s 5 3.2s 34.2s 10.2s 6 24.5s 2m 18s 7m 30s 6 3.2s 35.4s 10.2s 7 29.4s 2m 25s 8m 24s 7 3.2s 36.5s 10.1s 8 45.5s 2m 32s 10m 59s 8 3.2s 37.5s 10.0s 9 66.9s 2m 37s 12m 20s 9 3.1s 38.2s 10.0s 23 /31 Tar archive The Linux kernel 2.6.11.0 source (199 MB) Compressed size / Uncompressed size * 100% gzip bzip2 lzmash 1 27,8% 21,1% 21,1% 2 26,5% 19,7% 18,7% 3 25,7% 19,1% 16,7% 4 23,9% 18,7% 16,1% 5 22,9% 18,4% 15,6% 6 22,6% 18,2% 15,2% 7 22,5% 18,1% 14,8% 8 22,4% 17,9% 14,5% 9 22,4% 17,8% 14,3% 24 /31 Tar archive The Linux kernel 2.6.11.0 source (199 MB) Compression time Decompression time gzip bzip2 lzmash gzip bzip2 lzmash 1 8.3s 1m 9s 0m 45s 1 2.8s 12.8s 7.7s 2 8.7s 1m 22s 1m 45s 2 2.7s 19.4s 6.9s 3 9.8s 1m 34s 5m 10s 3 2.6s 23.8s 6.4s 4 11.1s 1m 45s 5m 43s 4 2.5s 26.4s 6.3s 5 13.8s 1m 57s 7m 39s 5 2.5s 28.3s 6.3s 6 17.8s 2m 2s 8m 23s 6 2.4s 29.6s 6.2s 7 20.7s 2m 11s 9m 11s 7 2.4s 30.6s 6.2s 8 29.7s 2m 21s 11m 34s 8 2.4s 31.3s 6.1s 9 40.9s 2m 26s 12m 31s 9 2.4s 32.1s 6.1s 25 /31 XMMS 1.2.10 binary package (5.2 MB)(Slackware 10.1) Compressed size / Uncompressed size * 100% gzip bzip2 lzmash 1 39,3% 32,8% 26,0% 2 38,4% 29,3% 20,7% 3 37,7% 28,0% 18,8% 4 36,9% 27,0% 18,3% 5 36,2% 26,6% 18,0% 6 36,0% 26,1% 17,9% 7 35,9% 26,0% 17,9% 8 35,9% 25,7% 17,8% 9 35,8% 25,2% 17,8% 26 /31 XMMS 1.2.10 binary package (5.2 MB)(Slackware 10.1) Compression time Decompression time gzip bzip2 lzmash gzip bzip2 lzmash 1 0.3s 2.4s 1.4s 1 0.1s 0.4s 0.3s 2 0.3s 2.9s 2.7s 2 0.1s 0.6s 0.2s 3 0.4s 3.2s 6.2s 3 0.1s 0.7s 0.2s 4 0.4s 3.3s 6.6s 4 0.1s 0.8s 0.2s 5 0.5s 4.6s 8.2s 5 0.1s 0.9s 0.2s 6 0.7s 5.6s 8.5s 6 0.1s 0.9s 0.2s 7 0.8s 4.7s 8.6s 7 0.1s 0.9s 0.2s 8 1.1s 4.9s 10.5s 8 0.1s 1.0s 0.2s 9 1.8s 5.1s 10.5s 9 0.1s 1.0s 0.2s 27 /31 XMMS 1.2.10 source tarball (15.2 MB) Compressed size / Uncompressed size * 100% gzip bzip2 lzmash 1 29,5% 23,2% 21,2% 2 28,6% 19,9% 13,3% 3 27,9% 18,3% 12,0% 4 26,4% 17,2% 11,3% 5 25,7% 16,7% 10,8% 6 25,4% 16,2% 10,3% 7 25,3% 15,7% 9,7% 8 25,3% 15,4% 9,6% 9 25,3% 15,1% 9,6% 28 /31 XMMS 1.2.10 source tarball (15.2 MB) Compression time Decompression time gzip bzip2 lzmash gzip bzip2 lzmash 1 0.7s 6.1s 3.5s 1 0.2s 1.0s 0.6s 2 0.7s 7.3s 6.0s 2 0.2s 1.5s 0.4s 3 0.8s 8.5s 19.0s 3 0.2s 1.9s 0.4s 4 0.9s 9.9s 19.9s 4 0.2s 2.1s 0.4s 5 1.1s 11.2s 28.9s 5 0.2s 2.3s 0.4s 6 1.4s 11.0s 30.1s 6 0.2s 2.5s 0.4s 7 1.7s 12.5s 30.9s 7 0.2s 2.6s 0.4s 8 2.5s 15.9s 41.7s 8 0.2s 2.7s 0.4s 9 2.9s 17.5s 41.7s 9 0.2s 2.8s 0.4s 29 /31 Memory requirements RAM usage on compression gzip bzip2 lzmash 1 <1 MB 2 MB 2 MB 2 <1 MB 2 MB 3 <1 MB 4 RAM usage on decompression gzip bzip2 lzmash 1 <1 MB 1 MB 1 MB 12 MB 2 <1 MB 2 MB 2 MB 3 MB 12 MB 3 <1 MB 2 MB 1 MB <1 MB 4 MB 16 MB 4 <1 MB 2 MB 2 MB 5 <1 MB 5 MB 26 MB 5 <1 MB 3 MB 3 MB 6 <1 MB 5 MB 45 MB 6 <1 MB 3 MB 5 MB 7 <1 MB 6 MB 83 MB 7 <1 MB 3 MB 9 MB 8 <1 MB 7 MB 159 MB 8 <1 MB 4 MB 17 MB 9 <1 MB 7 MB 311 MB 9 <1 MB 4 MB 33 MB 30 /31 Спасибо за внимание! 31/31