diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,5 @@ +# Revision history for shannon-fano + +## 0.1.0.0 -- 02/11/2018 + +* First version. diff --git a/Codec/Compression/ShannonFano.hs b/Codec/Compression/ShannonFano.hs new file mode 100644 --- /dev/null +++ b/Codec/Compression/ShannonFano.hs @@ -0,0 +1,218 @@ +module Codec.Compression.ShannonFano ( + frequency, + probability, + compress, + compressToFile, + code, + genCodeTable, + genDecodeTable, + readDecodeTable, + decode, + decompressFromFile + ) where + +import Data.List (group, sort, sortBy) +import Data.List.Split (chunksOf) +import Data.Char (intToDigit) +import Numeric (readInt, showIntAtBase) +import System.IO +import qualified Data.ByteString as BS + +----- * Auxiliar data types +-- + +-- | List with every character associated to its frequency/probability. +-- +type Table a = [(Char, a)] + +-- | Intermediate structure used to create a 'CodeTable'. +type Encoding a = [((Char, a), String)] + +-- | List of every character and its binary code. +type CodeTable = [(Char, String)] + +-- | List of the binary code associated to its character. +type DecodeTable = [(String, Char)] + +----- * Auxiliar functions +split :: (a -> b) -> (a -> c) -> a -> (b, c) +split f g x = (f x, g x) + +(><) :: (a -> b) -> (c -> d) -> (a, c) -> (b, d) +f >< g = split (f . fst) (g . snd) + +divide :: (Ord a, Num a) => Encoding a -> (Encoding a, Encoding a) +divide [] = ([],[]) +divide (h:t) = let index = divide' t [h] 1 + in (map (id >< (flip (++) "0"))) >< (map (id >< (flip (++) "1"))) $ splitAt index (h:t) + where + divide' [] _ i = i + divide' (x:xs) l i | (sum $ map (snd . fst) (x:xs)) < (sum $ map (snd . fst) xs) = divide' t (x:l) (i+1) + | otherwise = i + +encode :: Table a -> Encoding a +encode = map (split id (const "")) + +code' :: (Num a, Ord a) => Encoding a -> Encoding a +code' a = let (l,r) = divide a + in code'' l ++ code'' r + where + code'' [] = [] + code'' [x] = [x] + code'' s = code' s + +string2dec :: (Num a) => String -> a +string2dec s = fst $ (readInt 2 c d s) !! 0 + where + c x = x == '1' || x == '0' + d x = if x == '1' then 1 else 0 + +dec2binStr :: (Integral a, Show a) => a -> String +dec2binStr a = showIntAtBase 2 intToDigit a "" + +getFromBinary :: FilePath -> IO (Int, [Int]) +getFromBinary f = do + fH <- openBinaryFile f ReadMode + r <- BS.hGetContents fH + (l, wrds) <- return . split head tail . BS.unpack $ r + hClose fH + return (fromIntegral l, map fromIntegral wrds) + +----- * ShannonFano functions + +-- | Gives the frequency table of all characters in a string. +-- +frequency :: String -- ^ Input string + -> Table Int -- ^ Resulting table +frequency = sortBy cmp . map (split head length) . group . sort + where + cmp x y = if snd x < snd y then GT else LT + +-- | Gives the probability table of all characters in a string. +-- +probability :: String -- ^ Input string + -> Table Float -- ^ Resulting table +probability s = sortBy cmp . map (split head prob) . group . sort $ s + where + totalLength = length s + cmp x y = if snd x < snd y then GT else LT + prob x = (fromIntegral $ length x) / (fromIntegral totalLength) + +-- | Generates a 'CodeTable' +-- +genCodeTable :: (Num a, Ord a) => Encoding a -- ^ Input encoding + -> CodeTable -- ^ Resulting code table +genCodeTable = map (fst >< id) + +-- | Generates a 'DecodeTable' +-- +genDecodeTable :: (Num a, Ord a) => Encoding a -- ^ Input encoding + -> DecodeTable -- ^ Resulting decode table +genDecodeTable = map (split snd fst) . genCodeTable + + +-- | Given a 'Table' encodes it by applying the Shannon-fano +-- algorithm. +-- +code :: (Num a, Ord a) => Table a -- ^ Input table + -> Encoding a -- ^ Resulting encoding +code = code' . encode + +-- | Compresses a string by applying a table generator function +-- and uses it to create a string of 0's and 1's. +-- +compress :: (Num a, Ord a) => (String -> Table a) -- ^ 'frequency' or 'probability' can be applied + -> String -- ^ String to compress + -> Maybe String -- ^ Compressed, 0's and 1's, resulting string +compress f s = let encoding = code . f $ s + codeTable = genCodeTable encoding + in (go codeTable s) + where + go _ [] = Just "" + go e (h:t) = (++) <$> lookup h e <*> go e t + +-- | Compresses a string to a file. +-- +-- Calls the 'compress' function on the input string and +-- writes the binary code in a file. +-- +-- The resulting files are: +-- - 'out.bin' <- binary compressed file +-- - 'decode.dat' <- contains the decoding table of out.bin +compressToFile :: (Num a, Ord a) => (String -> Table a) -- ^ 'frequency' or 'probability' can be applied + -> String -- ^ String to compress + -> IO () +compressToFile f s = let decodeTable = genDecodeTable . code . f $ s + in do + fH <- openBinaryFile "out.bin" WriteMode + result <- return $ compress f s + case result of + Nothing -> hClose fH + Just r -> do + writeFile "decode.dat" (show decodeTable) + chunks <- return $ map string2dec . chunksOf 8 $ r + chunksL <- return $ (fromIntegral (8 - length r `mod` 8 )) : chunks -- Adds the length of the final byte + BS.hPut fH (BS.pack chunksL) + hClose fH + +-- | Reads a 'DecodeTable' from a file +-- +readDecodeTable :: FilePath -- ^ File path for the decode table + -> IO (Maybe DecodeTable) -- ^ Decode table +readDecodeTable fp = do + dtContent <- readFile fp + return . readDT $ dtContent + where + readDT :: String -> Maybe DecodeTable + readDT = fmap fst . safeHead . reads + safeHead [] = Nothing + safeHead (h:_) = Just h + +-- | Decodes a 'String' (made out of 0's and 1's) given a 'DecodeTable' +-- +decode :: DecodeTable -- ^ Decoding table + -> String -- ^ Example "0110110111" + -> Maybe String -- ^ Resulting string +decode _ "" = Nothing +decode dt (h:t) = decode' dt t [h] + where + decode' dtt [] l = do + case (lookup l dtt) of + Nothing -> Just "" + (Just r) -> (:) <$> (Just r) <*> (Just "") + decode' dtt (x:xs) l = do + case (lookup l dtt) of + Nothing -> decode' dtt xs (l++[x]) + (Just r) -> (:) <$> (Just r) <*> (decode' dtt xs [x]) + +-- | Decompresses a file given a decoding table file and a compressed +-- binary file. +-- +-- If the resulting output file is empty ("") the default name is +-- "result.dat" +decompressFromFile :: FilePath -- ^ File holding the decoding table info + -> FilePath -- ^ File holding the compressed binary + -> String -- ^ Resulting file to output. + -> IO () +decompressFromFile dtf bf rf = do + rfH <- case rf of + "" -> openFile "result.dat" WriteMode + _ -> openFile rf WriteMode + dt <- readDecodeTable dtf + case dt of + Nothing -> hClose rfH + Just r -> do + (l, wrds) <- getFromBinary bf + binaryString <- return $ fixBinary (l,wrds) + decompressed <- return $ decode r $ binaryString + case decompressed of + Nothing -> hClose rfH + Just d -> do + hPutStr rfH d + hClose rfH + where + fixBinary (l, r) = let b = map dec2binStr r + paddedB = map pad8 b + in concat $ init paddedB ++ [(drop (fromIntegral l) $ last paddedB)] + pad8 s = let rest = 8 - 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If not, see . + +Also add information on how to contact you by electronic and paper mail. + + If the program does terminal interaction, make it output a short +notice like this when it starts in an interactive mode: + + Copyright (C) + This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. + This is free software, and you are welcome to redistribute it + under certain conditions; type `show c' for details. + +The hypothetical commands `show w' and `show c' should show the appropriate +parts of the General Public License. Of course, your program's commands +might be different; for a GUI interface, you would use an "about box". + + You should also get your employer (if you work as a programmer) or school, +if any, to sign a "copyright disclaimer" for the program, if necessary. +For more information on this, and how to apply and follow the GNU GPL, see +. + + The GNU General Public License does not permit incorporating your program +into proprietary programs. If your program is a subroutine library, you +may consider it more useful to permit linking proprietary applications with +the library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. But first, please read +. diff --git a/README.md b/README.md new file mode 100644 --- /dev/null +++ b/README.md @@ -0,0 +1,208 @@ +# Shannon-Fano compression algorithm library +> Haskell implementation + +This library offers a set of functions to compress files into binary code +applying the Shannon-Fano compression algorithm. + +https://en.wikipedia.org/wiki/Shannon%E2%80%93Fano_coding + +## Installing / Getting started + +I'm currently working to get this library on Hackage. So meanwhile +you can start using it by building it. + +```shell +$ git clone https://github.com/bolt12/shannon-fano.git +$ cd shannon-fano/ +$ cabal configure +$ cabal build +$ cabal install +``` + +You can see if it's correctly installed by going into ghci and see if you can import the +library. + +```shell +$ ghci +> import Codec.Compression.ShannonFano +> +``` + +## Use examples + +To get the compressed binary string of a certain value. + +```Haskell +import Codec.Compression.ShannonFano + +main :: IO () +main = putStrLn . show . compress frequency $ "test" +``` + +And you should see. + +```shell +> main +Just "010110" +``` + +--- + +To generate only the coding table of some value. + +```Haskell +import Codec.Compression.ShannonFano + +main :: IO () +main = putStrLn . show . genCodeTable . code . frequency $ "test" +``` + +And you should see. + +```shell +> main +[('t',"0"),('e',"10"),('s',"11")] +``` + +--- + +To make a program that compresses a given file. + +```Haskell +import Codec.Compression.ShannonFano +import System.Environment + +main :: IO () +main = do + [file] <- getArgs + content <- readFile file + compressTofile frequency content +``` + +And you should get two resulting files: + - out.bin: Has the binary of the compressed data + - decode.dat: Has the decoding table structure + +--- + +To make a program that decompresses a given binary file. + +```Haskell +import Codec.Compression.ShannonFano +import System.Environment + +main :: IO () +main = do + [decTableF, binaryF] <- getArgs + decompressFromFile decTableF binaryF "" +``` + +And you should get one resulting file: + - result.dat: Has the binary of the compressed data + +You can check they are equal. + +```shell +$ diff result.dat test.txt +$ +``` + +## Performance and compression + +Testing the compressor program for a lorem ipsum text file of 921 words: + +```shell +$ time ./compress test.txt + +real 0m0.075s +user 0m0.067s +sys 0m0.007s +``` + +Compression: + +```shell +$ ls -lh out.bin test.txt | cut -d " " -f5 +5.7K +6.5K +``` + +_Total ~ 12%_ + +--- + +Testing the compressor program with 1M of random data: + +```shell +$ base64 /dev/urandom | head -c 1000000 > test2.txt +$ time ./compress test2.txt + +real 0m30.411s +user 0m27.930s +sys 0m2.187s +``` + +Compression: + +```shell +$ ls -lh out.bin test2.txt | cut -d " " -f5 +4.0M +977K +``` + +_Total ~ -312%_ + +--- + +Testing the compressor program with a 70K file containing repetitions of 5 characters: + +```shell +$ time ./compress test3.txt + +real 0m0.511s +user 0m0.489s +sys 0m0.017s +``` + +Compression: + +```shell +$ ls -lh out.bin test3.txt | cut -d " " -f5 +19K +70K +``` + +_Total ~ 73%_ + +Decompression: + +```shell +$ time ./decompress decode.dat out.bin + +real 0m0.128s +user 0m0.105s +sys 0m0.023s +``` + +--- + +### Conclusion + +As you can see, this algorithm performs very badly, in general with random and large data. + +Also my implementation is far from efficient, if you have any suggestion on how to improve my solution +I'd be more than happy to hear it! + +## Contributing + +If you'd like to contribute, please fork the repository and use a feature +branch. Pull requests are warmly welcome. + +## Links + +- Repository: https://github.com/bolt12/shannon-fano/ +- Issue tracker: https://github.com/bolt12/shannon-fano/issues + +## Licensing + +The code in this project is licensed under GPL3 license. diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple +main = defaultMain diff --git a/shannon-fano.cabal b/shannon-fano.cabal new file mode 100644 --- /dev/null +++ b/shannon-fano.cabal @@ -0,0 +1,86 @@ +-- Initial shannon-fano.cabal generated by cabal init. For further +-- documentation, see http://haskell.org/cabal/users-guide/ + +-- The name of the package. +name: shannon-fano + +-- The package version. See the Haskell package versioning policy (PVP) +-- for standards guiding when and how versions should be incremented. +-- https://wiki.haskell.org/Package_versioning_policy +-- PVP summary: +-+------- breaking API changes +-- | | +----- non-breaking API additions +-- | | | +--- code changes with no API change +version: 0.1.0.0 + +-- A short (one-line) description of the package. +synopsis: Shannon-fano compression algorithm implementation in Haskell + +-- A longer description of the package. +-- description: + +-- URL for the project homepage or repository. +homepage: www.github.com/bolt12/shannon-fano + +-- The license under which the package is released. +license: GPL-3 + +-- The file containing the license text. +license-file: LICENSE + +-- The package author(s). +author: Armando Santos + +-- An email address to which users can send suggestions, bug reports, and +-- patches. +maintainer: armandoifsantos@gmail.com + +-- A copyright notice. +-- copyright: + +category: System + +build-type: Simple + +-- Extra files to be distributed with the package, such as examples or a +-- README. +extra-source-files: CHANGELOG.md, + README.md + +-- Constraint on the version of Cabal needed to build this package. +cabal-version: >=1.10 + + + +test-suite tests + type: exitcode-stdio-1.0 + hs-source-dirs: tests + main-is: QuickTests.hs + build-depends: base, + shannon-fano, + QuickCheck + default-language: Haskell2010 + +library + -- Modules exported by the library. + exposed-modules: Codec.Compression.ShannonFano + + -- Modules included in this library but not exported. + -- other-modules: + + -- LANGUAGE extensions used by modules in this package. + -- other-extensions: + + -- Other library packages from which modules are imported. + build-depends: base >=4.12 && <4.13, + bytestring >= 0.10.8.2, + split >= 0.2.3.3 && < 0.3 + + -- Directories containing source files. + -- hs-source-dirs: + + -- Base language which the package is written in. + default-language: Haskell2010 + + -- Ghc option flags + ghc-options: -Wall + diff --git a/tests/QuickTests.hs b/tests/QuickTests.hs new file mode 100644 --- /dev/null +++ b/tests/QuickTests.hs @@ -0,0 +1,23 @@ +import Codec.Compression.ShannonFano +import Control.Monad (join) +import Text.Printf (printf) +import Test.QuickCheck (quickCheck, (==>), Property) + +prop_freq_id :: String -> Property +prop_freq_id s = length s > 1 ==> let dt = genDecodeTable . code . frequency $ s + in join (decode dt <$> compress frequency s) == Just s + +prop_prob_id :: String -> Property +prop_prob_id s = length s > 1 ==> let dt = genDecodeTable . code . probability $ s + in join (decode dt <$> compress frequency s) == Just s + +prop_rev_table :: String -> Bool +prop_rev_table s = let ct = genCodeTable . code . frequency $ s + dt = genDecodeTable . code . frequency $ s + in dt == map swap ct + where + swap = (,) <$> snd <*> fst + +tests = [("prop_freq_id", quickCheck prop_freq_id), ("prop_prob_id", quickCheck prop_prob_id), ("prop_rev_table", quickCheck prop_rev_table)] + +main = mapM_ (\(s,a) -> printf "%-25s: " s >> a) tests