diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -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
diff --git a/Codec/Compression/ShannonFano.hs b/Codec/Compression/ShannonFano.hs
deleted file mode 100644
--- a/Codec/Compression/ShannonFano.hs
+++ /dev/null
@@ -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
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,674 +1,21 @@
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-Also add information on how to contact you by electronic and paper mail.
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-if any, to sign a "copyright disclaimer" for the program, if necessary.
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-.
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
- The GNU General Public License does not permit incorporating your program
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-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
-.
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+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,6 +1,12 @@
# Shannon-Fano compression algorithm library
> Haskell implementation
+[](https://github.com/bolt12/shannon-fano/actions)
+[](https://travis-ci.org/bolt12/shannon-fano)
+[](https://hackage.haskell.org/package/shannon-fano)
+[](http://stackage.org/lts/package/shannon-fano)
+[](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
diff --git a/app/Main.hs b/app/Main.hs
new file mode 100644
--- /dev/null
+++ b/app/Main.hs
@@ -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 ()
diff --git a/shannon-fano.cabal b/shannon-fano.cabal
--- a/shannon-fano.cabal
+++ b/shannon-fano.cabal
@@ -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
+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
-
diff --git a/src/Codec/Compression/ShannonFano.hs b/src/Codec/Compression/ShannonFano.hs
new file mode 100644
--- /dev/null
+++ b/src/Codec/Compression/ShannonFano.hs
@@ -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:
+-- - '' <- binary compressed file
+-- - '.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
diff --git a/src/Codec/Compression/ShannonFano/Internal.hs b/src/Codec/Compression/ShannonFano/Internal.hs
new file mode 100644
--- /dev/null
+++ b/src/Codec/Compression/ShannonFano/Internal.hs
@@ -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")
diff --git a/tests/Main.hs b/tests/Main.hs
new file mode 100644
--- /dev/null
+++ b/tests/Main.hs
@@ -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
diff --git a/tests/QuickTests.hs b/tests/QuickTests.hs
deleted file mode 100644
--- a/tests/QuickTests.hs
+++ /dev/null
@@ -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