HexString.hs

   1 -- This file is part of htalkat
   2 -- Copyright (C) 2021 Martin Bays <mbays@sdf.org>
   3 --
   4 -- This program is free software: you can redistribute it and/or modify
   5 -- it under the terms of version 3 of the GNU General Public License as
   6 -- published by the Free Software Foundation, or any later version.
   7 --
   8 -- You should have received a copy of the GNU General Public License
   9 -- along with this program.  If not, see http://www.gnu.org/licenses/.
  10
  11 {-# LANGUAGE Safe #-}
  12
  13 module HexString where
  14
  15 import           Data.ByteString (ByteString, pack, unpack)
  16
  17 parseHexString :: String -> Maybe ByteString
  18 parseHexString s = pack <$> parseHexString' s
  19     where
  20     parseHexString' (a:b:c) = do
  21         ha <- fromHex a
  22         hb <- fromHex b
  23         (16 * ha + hb :) <$> parseHexString' c
  24         where
  25         fromHex '0' = Just 0
  26         fromHex '1' = Just 1
  27         fromHex '2' = Just 2
  28         fromHex '3' = Just 3
  29         fromHex '4' = Just 4
  30         fromHex '5' = Just 5
  31         fromHex '6' = Just 6
  32         fromHex '7' = Just 7
  33         fromHex '8' = Just 8
  34         fromHex '9' = Just 9
  35         fromHex 'a' = Just 10
  36         fromHex 'b' = Just 11
  37         fromHex 'c' = Just 12
  38         fromHex 'd' = Just 13
  39         fromHex 'e' = Just 14
  40         fromHex 'f' = Just 15
  41         fromHex 'A' = Just 10
  42         fromHex 'B' = Just 11
  43         fromHex 'C' = Just 12
  44         fromHex 'D' = Just 13
  45         fromHex 'E' = Just 14
  46         fromHex 'F' = Just 15
  47         fromHex _   = Nothing
  48     parseHexString' [] = Just []
  49     parseHexString' _ = Nothing
  50
  51 showHexString :: ByteString -> String
  52 showHexString = concatMap showHexWord8 . unpack
  53     where showHexWord8 w =
  54             let (a,b) = quotRem w 16
  55                 hex = ("0123456789abcdef" !!) . fromIntegral
  56             in hex a : hex b : ""