packBits.hs

Haskell

Public Domain

Pack & unpack bits into bytes in ascending or descending order

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bit bits bitwise byte bytes Haskell pack unpack 
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import Word (Word8)
import Data.Bits (testBit)

packBitsAsc, packBitsDesc :: [Bool] -> [Word8]

packBitsAsc [] = []
packBitsAsc b = fromIntegral byte : packBitsAsc (drop 8 b)
 where bits = take 8 $ take 8 b ++ repeat False
       byte = foldr (\tf a -> a*2 + fromEnum tf) 0 bits

packBitsDesc [] = []
packBitsDesc b = fromIntegral byte : packBitsAsc (drop 8 b)
 where bits = take 8 $ take 8 b ++ repeat False
       byte = foldl (\a tf -> a*2 + fromEnum tf) 0 bits

unpackBitsAsc, unpackBitsDesc :: [Word8] -> [Bool]
unpackBitsAsc bits = [testBit b i | b <- bits, i <- [0..7]]
unpackBitsDesc bits = [testBit b i | b <- bits, i <- [7, 6 .. 0]]