shannon-fano 0.1.0.1 → 1.0.0.0

raw patch · 10 files changed

+460/−1099 lines, 10 filesdep +optparse-genericdep −splitdep ~basedep ~bytestringnew-component:exe:shannon-fanoPVP ok

version bump matches the API change (PVP)

Dependencies added: optparse-generic

Dependencies removed: split

Dependency ranges changed: base, bytestring

API changes (from Hackage documentation)

Files

• CHANGELOG.md +9/−3
• Codec/Compression/ShannonFano.hs +0/−218
• LICENSE +17/−670
• README.md +65/−111
• app/Main.hs +41/−0
• shannon-fano.cabal +57/−74
• src/Codec/Compression/ShannonFano.hs +140/−0
• src/Codec/Compression/ShannonFano/Internal.hs +110/−0
• tests/Main.hs +21/−0
• tests/QuickTests.hs +0/−23

@@ -1,5 +1,11 @@-# Revision history for shannon-fano+# Changelog -## 0.1.0.0 -- 02/11/2018+`shannon-fano` uses [PVP Versioning][1].+The changelog is available [on GitHub][2]. -* First version.+## 1.0.0.0++* Stable version.++[1]: https://pvp.haskell.org+[2]: https://github.com/bolt12/shannon-fano/releases

@@ -1,218 +0,0 @@-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 - length s-                     in replicate rest '0' ++ s

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If not, see <http://www.gnu.org/licenses/>.--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:+MIT License -    <program>  Copyright (C) <year>  <name of author>-    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.+Copyright (c) 2020 Armando Santos -The hypothetical commands `show w' and `show c' should show the appropriate-parts of the General Public License.  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@@ -1,6 +1,12 @@ # Shannon-Fano compression algorithm library > Haskell implementation +[![GitHub CI](https://github.com/bolt12/shannon-fano/workflows/CI/badge.svg)](https://github.com/bolt12/shannon-fano/actions)+[![Build status](https://img.shields.io/travis/bolt12/shannon-fano.svg?logo=travis)](https://travis-ci.org/bolt12/shannon-fano)+[![Hackage](https://img.shields.io/hackage/v/shannon-fano.svg?logo=haskell)](https://hackage.haskell.org/package/shannon-fano)+[![Stackage Lts](http://stackage.org/package/shannon-fano/badge/lts)](http://stackage.org/lts/package/shannon-fano)+[![Stackage Nightly](http://stackage.org/package/shannon-fano/badge/nightly)](http://stackage.org/nightly/package/shannon-fano)+ This library offers a set of functions to compress files into binary code applying the Shannon-Fano compression algorithm. @@ -8,15 +14,14 @@  ## Installing / Getting started -### Cabal+### Stack  This package is now availablein Hackage at https://hackage.haskell.org/package/shannon-fano-0.1.0.0  So you just need to:  ```shell-$ cabal update-$ cabal install shannon-fano+$ stack install shannon-fano ```  ### Manually@@ -24,193 +29,142 @@ ```shell $ git clone https://github.com/bolt12/shannon-fano.git $ cd shannon-fano/-$ cabal configure-$ cabal build-$ cabal install+$ stack install ```  #### Build documentation  ```shell $ cd shannon-fano/-$ cabal haddock+$ stack haddock ```  ### See for yourself -You can see if it's correctly installed by going into ghci and see if you can import the-library.+You can see if it's correctly installed by doing calling the program in the terminal. You+should see the following:  ```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"-```+> shannon-fano -h+Compress contents using the Shannon-Fano algorithm -And you should see.+Usage: shannon-fano [--decompress STRING] [--input STRING] [--output STRING] -```shell-> main-Just "010110"+Available options:+-h,--help                Show this help text+--decompress STRING      Decompress with decode table file name.+--input STRING           Input content file name. If not specified will be+read from stdin.+--output STRING          Output result file name. If not specified will be+'out.bin' or 'out.bin.dat' depending on the action ``` ------To generate only the coding table of some value.--```Haskell-import Codec.Compression.ShannonFano--main :: IO ()-main = putStrLn . show . genCodeTable . code . frequency $ "test"-```+## Use examples -And you should see.+The program is able to read from stdin if no input file is provided like so:  ```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+> shannon-fano+test+> ``` -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+This will create a 'out.bin' file and a 'out.bin.tab' file (which contains the decode+table), which you can decompress: -main :: IO ()-main = do-    [decTableF, binaryF] <- getArgs-    decompressFromFile decTableF binaryF ""+```shell+> shannon-fano --decompress out.bin.tab --input out.bin ``` -And you should get one resulting file:- - result.dat: Has the binary of the compressed data--You can check they are equal.+If no output file name is provided, this should create a new file called 'out.dat':  ```shell-$ diff result.dat test.txt-$+> cat out.dat+test ```  ## Performance and compression -Testing the compressor program for a lorem ipsum text file of 921 words:+Testing the compressor program for a lorem ipsum text file of 1000 words:  ```shell-$ time ./compress test.txt+> time shannon-fano --input test.txt -real	0m0.075s-user	0m0.067s-sys     0m0.007s+real    0m0.074s+user    0m0.060s+sys     0m0.025s ```  Compression:  ```shell-$ ls -lh out.bin test.txt | cut -d " " -f5-5.7K-6.5K+> ls -lh out.bin test.txt | cut -d " " -f5+3.4K+6.4K ``` -_Total ~ 12%_+_Total ~ 47%_  ---  Testing the compressor program with 1M of random data:  ```shell-$ base64 /dev/urandom | head -c 1000000 > test2.txt-$ time ./compress test2.txt+> base64 /dev/urandom | head -c 1000000 > test.txt+> time shannon-fano --input test.txt -real	0m30.411s-user	0m27.930s-sys     0m2.187s+real    0m2.648s+user    0m2.321s+sys     0m1.305s ```  Compression:  ```shell-$ ls -lh out.bin test2.txt | cut -d " " -f5-4.0M+> ls -lh out.bin test.txt | cut -d " " -f5+737K 977K ``` -_Total ~ -312%_+_Total ~ 15%_  --- -Testing the compressor program with a 70K file containing repetitions of 5 characters:+Testing the compressor program with a 2.1M file containing repetitions of 5 characters:  ```shell-$ time ./compress test3.txt+> time shannon-fano --input test.txt -real	0m0.511s-user	0m0.489s-sys     0m0.017s+real    0m2.356s+user    0m2.069s+sys     0m1.499s ```  Compression:  ```shell-$ ls -lh out.bin test3.txt | cut -d " " -f5-19K-70K+> ls -lh out.bin test.txt | cut -d " " -f5+734K+2.1M ``` -_Total ~ 73%_+_Total ~ 65%_  Decompression:  ```shell-$ time ./decompress decode.dat out.bin+> time shannon-fano --decompress out.bin.tab --input out.bin -real	0m0.128s-user	0m0.105s-sys     0m0.023s+real    0m6.374s+user    0m6.252s+sys     0m1.394s ```  ---  ### 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!+As you can see, this algorithm performs worse, in general, in terms of compression, with random and large data.  ## Contributing 

@@ -0,0 +1,41 @@+{-# LANGUAGE TupleSections #-}+{-# LANGUAGE StandaloneDeriving #-}+{-# LANGUAGE TypeOperators #-}+{-# LANGUAGE DataKinds #-}+{-# LANGUAGE FlexibleInstances #-}+{-# LANGUAGE DeriveGeneric #-}+{-# LANGUAGE OverloadedStrings #-}++module Main (main) where++import qualified Codec.Compression.ShannonFano as SF+import Options.Generic+import System.IO++data Options w = Options+    { decompress :: w ::: Maybe FilePath <?> "Decompress with decode table file name."+    , input :: w ::: Maybe FilePath <?> "Input content file name. If not specified will be read from stdin."+    , output :: w ::: Maybe FilePath <?> "Output result file name. If not specified will be 'out.bin' or 'out.dat' depending on the action"+    } deriving (Generic)++instance ParseRecord (Options Wrapped)+deriving instance Show (Options Unwrapped)++main :: IO ()+main = do+  x <- unwrapRecord "Compress contents using the Shannon-Fano algorithm"+  (out, fH) <- case (input x, output x, decompress x) of+    (Nothing      , Nothing , Nothing) -> return ("out.bin", stdin)+    (Nothing      , Nothing , Just _)  -> return ("out.dat", stdin)+    (Nothing      , Just out, _)       -> return (out      , stdin)+    (Just filename, Nothing , Nothing) -> ("out.bin", ) <$> openFile filename ReadMode+    (Just filename, Nothing , Just _)  -> ("out.dat", ) <$> openFile filename ReadMode+    (Just filename, Just out, _)       -> (out      , ) <$> openFile filename ReadMode+  case decompress x of+    Nothing        -> SF.compressToFile fH out+    Just tableFile -> do+      table <- read <$> readFile tableFile+      r <- SF.decompressFromFile fH table out+      case r of+        Left e -> print e >> hClose fH+        _ -> return ()

@@ -1,86 +1,69 @@--- Initial shannon-fano.cabal generated by cabal init.  For further--- documentation, see http://haskell.org/cabal/users-guide/---- The name of the package.+cabal-version:       2.4 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:             0.1.0.1---- 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.+version:             1.0.0.0+synopsis:            Shannon-fano compression algorithm in Haskell+description:         Shannon-fano compression algorithm in Haskell program and API+homepage:            https://github.com/bolt12/shannon-fano+bug-reports:         https://github.com/bolt12/shannon-fano/issues+license:             MIT 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-+maintainer:          Armando Santos <armandoifsantos@gmail.com>+copyright:           2020 Armando Santos 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+category:            Codec+extra-doc-files:     README.md+                     CHANGELOG.md+tested-with:         GHC == 8.6.5+                     GHC == 8.8.3 +source-repository head+  type:                git+  location:            https://github.com/bolt12/shannon-fano.git +common common-options+  build-depends:       base >= 4.12.0.0 && < 5,+                       bytestring -any,+                       optparse-generic -any+  +  ghc-options:         -Wall+                       -Wcompat+                       -Widentities+                       -Wincomplete-uni-patterns+                       -Wincomplete-record-updates+  if impl(ghc >= 8.0)+    ghc-options:       -Wredundant-constraints+  if impl(ghc >= 8.2)+    ghc-options:       -fhide-source-paths+  if impl(ghc >= 8.4)+    ghc-options:       -Wmissing-export-lists+                       -Wpartial-fields+  if impl(ghc >= 8.8)+    ghc-options:       -Wmissing-deriving-strategies -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+  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+  import:              common-options+  hs-source-dirs:      src+  exposed-modules:     Codec.Compression.ShannonFano+                       Codec.Compression.ShannonFano.Internal -  -- Directories containing source files.-  --  hs-source-dirs:      +executable shannon-fano+  import:              common-options+  hs-source-dirs:      app+  main-is:             Main.hs+  build-depends:       shannon-fano+  ghc-options:         -threaded+                       -rtsopts+                       -with-rtsopts=-N -  -- Base language which the package is written in.+test-suite test+  import:              common-options+  type:                exitcode-stdio-1.0+  hs-source-dirs:      tests+  main-is:             Main.hs+  build-depends:       base,+                       shannon-fano,+                       QuickCheck   default-language:    Haskell2010--  -- Ghc option flags-  ghc-options: -Wall-

@@ -0,0 +1,140 @@+{-# LANGUAGE OverloadedStrings #-}++module Codec.Compression.ShannonFano where++import Codec.Compression.ShannonFano.Internal+import Control.Arrow+import Data.ByteString.Lazy (ByteString)+import qualified Data.ByteString as BS+import qualified Data.ByteString.Lazy as BSL+import Data.List (lookup, sortBy)+import Data.Word (Word8)+import System.IO++-- | Decode table error can happen when the wrong code table is provided.+data DecodeTableError = DecodeTableError+  deriving (Eq, Show)++-- | Gives the frequency table of all characters in a string.+frequency ::+  -- | Input string+  Input ->+  -- | Resulting table+  Table Int+frequency = map (BSL.head &&& (fromEnum . BSL.length)) . BSL.group . BSL.fromStrict . BS.sort . BSL.toStrict++-- | Gives the probability table of all characters in a string.+probability ::+  -- | Input string+  Input ->+  -- | Resulting table+  Table Float+probability s =+  let table = frequency s+      total = fromIntegral . fromEnum . BSL.length $ s+   in map (second ((/ total) . fromIntegral)) table++-- | Generates a 'DecodeTable'+genCodeTable ::+  -- | Input string+  Input ->+  -- | Resulting code table+  Table ByteString+genCodeTable s =+  let table = sortBy cmp $ probability s+   in aux (split table)+  where+    cmp :: (Word8, Float) -> (Word8, Float) -> Ordering+    cmp x y = if snd x < snd y then GT else LT+    aux :: (Table Float, Table Float) -> Table ByteString+    aux ([], []) = []+    aux ([(x, _)], [(y, _)]) = [(x, "0"), (y, "1")]+    aux ([(x, _)], r) = (x, "0") : map (second (BSL.append "1")) (aux (split r))+    aux (l, [(y, _)]) = map (second (BSL.append "0")) (aux (split l)) ++ [(y, "1")]+    aux (l, r) =+      let l2 = aux $ split l+          r2 = aux $ split r+       in map (second (BSL.append "0")) l2 ++ map (second (BSL.append "1")) r2++-- | Given a 'Table ByteString' compresses it by applying the Shannon-fano+--   algorithm.+compress ::+  -- | Input string+  Input ->+  -- | Result compressed+  ByteString+compress s = compressWithLeftover $ aux s (genCodeTable s)+  where+    aux :: ByteString -> Table ByteString -> ByteString+    aux s t+      | BSL.null s = BSL.empty+      | otherwise =+        let (x, xs) = (BSL.head &&& BSL.tail) s+            (Just r) = lookup x t+         in BSL.append r (aux xs t)++-- | Decompresses a compressed 'ByteString', given a code table+--+--   This fails if the code table does not have an entry for a given+--   character.+decompress ::+  -- | Coded input to decompress+  ByteString ->+  -- | Code table associated with the input+  Table ByteString ->+  -- | Result decompressed+  Maybe Input+decompress s t+  | BSL.null s = Just BSL.empty+  | BSL.null (decompressWithLeftover s) = Just BSL.empty+  | otherwise =+    let decomps = decompressWithLeftover s+        (x, xs) = (BSL.head &&& BSL.tail) decomps+     in aux (map (snd &&& fst) t) xs (BSL.singleton x)+  where+    aux :: [(ByteString, Word8)] -> ByteString -> ByteString -> Maybe ByteString+    aux dt ls l =+      if BSL.null ls+        then case lookup l dt of+          Nothing -> Just ""+          Just r -> BSL.cons <$> Just r <*> Just ""+        else+          let (h, t) = (BSL.head &&& BSL.tail) ls+           in case lookup l dt of+                Nothing -> aux dt t (BSL.append l (BSL.singleton h))+                (Just r) -> BSL.cons <$> Just r <*> aux dt t (BSL.singleton h)++-- | Reads contents from a handle and compresses it to a file.+--+--   The resulting files are:+--    - '<filename>' <- binary compressed file+--    - '<filename>.dat' <- contains the decoding table+compressToFile ::+  -- | Handle from where data will be read+  Handle ->+  -- | Output file name+  String ->+  IO ()+compressToFile h filename = do+  contents <- BSL.hGetContents h+  let compressed = compress contents+      decodeTable = genCodeTable contents+  writeFile (filename ++ ".tab") (show decodeTable)+  BSL.writeFile filename compressed++-- | Decompresses a file given a decoding table file and a compressed+--   compressed file.+decompressFromFile ::+  -- | Handle from where compressed data will be read+  Handle ->+  -- | Decode table+  Table ByteString ->+  -- | Output file name+  String ->+  IO (Either DecodeTableError ())+decompressFromFile h dt filename = do+  contents <- BSL.hGetContents h+  let decoded = decompress contents dt+  case decoded of+    Nothing -> return . Left $ DecodeTableError+    Just r -> Right <$> BSL.writeFile filename r

@@ -0,0 +1,110 @@+{-# LANGUAGE OverloadedStrings #-}++module Codec.Compression.ShannonFano.Internal+  ( Input,+    Table,+    split,+    chunksOf,+    decode,+    compressChunk,+    compressWithLeftover,+    decompressWithLeftover,+  )+where++import Control.Arrow ((&&&))+import Data.Bits+import Data.Bool (bool)+import Data.ByteString.Lazy (ByteString)+import qualified Data.ByteString.Lazy as BSL+import Data.Word++-- | Simple table used as an intermediate structure+type Table a = [(Word8, a)]++-- | Simple type alias to distinguish when something is an input or is+-- a coded or compressed 'Bytestring'.+type Input = ByteString++-- | Auxiliary split function.+--+-- This function splits a probabilities table in half where the sum of the+-- two halfs are as close as possible.+split :: Table Float -> (Table Float, Table Float)+split t = aux t []+  where+    aux [] l = (l, [])+    aux (x : xs) l+      | snd x + sum (map snd l) < sum (map snd xs) = aux xs (l ++ [x])+      | otherwise = (l ++ [x], xs)++-- | Takes a 'Bytestring' of 0s and 1s with length 8 and converts it to+-- a single 'Word8'.+--+-- Example:+-- @+-- compressChunk "00000001" == 1+-- @+compressChunk :: ByteString -> Word8+compressChunk s = aux s zeroBits+  where+    aux :: ByteString -> Word8 -> Word8+    aux s w+      | BSL.null s = w+      | otherwise =+        let (h, (t, n)) = (BSL.head &&& BSL.tail &&& BSL.length) s+         in case h of+              49 -> aux t (setBit w (fromEnum n - 1)) -- "1"+              48 -> aux t w                 -- "0"++-- | Creates a list of 'Bytestring' chunks.+chunksOf :: Int -> ByteString -> [ByteString]+chunksOf n = go+  where+    go t = case BSL.splitAt (toEnum n) t of+      (a, b)+        | BSL.null a -> []+        | otherwise -> a : go b++-- | Takes a full 'Bytestring' of 0s and 1s and compresses it in binary+-- form. This way, a 'ByteString' that represents a binary string is+-- converted in its compressed form, occupying only the necessary bits.+compress :: ByteString -> ByteString+compress = BSL.pack . map compressChunk . chunksOf 8++-- | The same as 'compress' but adds the size of the last byte to the+-- beginning of the compressed 'ByteString', since it might occupy less+-- than 8 bits.+compressWithLeftover :: ByteString -> ByteString+compressWithLeftover s = BSL.append (int2compressedBS (fromEnum (BSL.length s) `mod` 8)) (compress s)+  where+    int2compressedBS :: Int -> ByteString+    int2compressedBS n+      -- If n > 128 signifies that it does not fit in a 'Word8'+      | n > 128 = error "excess length greater than 8"+      | otherwise = compress . bool2BS . bitList $ n++-- | Takes a compressed 'Bytestring' and converts it into a 'Bytestring' of+-- only 0s and 1s.+decode :: ByteString -> ByteString+decode = BSL.concatMap (bool2BS . bitList)++-- | Takes a compressed 'Bytestring' and converts it into a 'Bytestring' of+-- only 0s and 1s, truncating the last byte accordingly, using the+-- information of the last byte's size.+decompressWithLeftover :: ByteString -> ByteString+decompressWithLeftover = BSL.concat . aux . (tail &&& (fromEnum . compressChunk . head)) . chunksOf 8 . decode+  where+    aux :: ([ByteString], Int) -> [ByteString]+    aux ([], _) = []+    aux ([x], 0) = [x] -- If 0 then there is no need to truncate+    aux ([x], i) = [BSL.drop (toEnum (8 - i)) x]+    aux (x : xs, i) = x : aux (xs, i)++-- | Creates a list of 'Bool's out of a bit.+bitList :: Bits a => a -> [Bool]+bitList x = map (testBit x) [7, 6 .. 0]++-- | Creates a bit 'ByteString' (a 'ByteString' full of 0s and 1s).+bool2BS :: [Bool] -> ByteString+bool2BS = BSL.concat . map (bool "0" "1")

@@ -0,0 +1,21 @@+module Main where++import Codec.Compression.ShannonFano+import Data.ByteString.Lazy (ByteString)+import qualified Data.ByteString.Lazy as BSL (pack)+import Text.Printf (printf)+import Test.QuickCheck (Arbitrary(..), quickCheck)++instance Arbitrary ByteString where+  arbitrary = BSL.pack <$> arbitrary++prop_id :: ByteString -> Bool+prop_id s = let dt = genCodeTable s+             in (`decompress` dt) (compress s) == Just s++tests :: [(String, IO ())]+tests = [ ("prop_id", quickCheck prop_id)+        ]++main :: IO ()+main = mapM_ (\(s,a) -> printf "%-25s: " s >> a) tests

@@ -1,23 +0,0 @@-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