src/Octet.hs

   1 module Octet where
   2
   3 import Bit
   4
   5 -- An Octet consists of eight bits. For our purposes, the most
   6 -- significant bit will come "first." That is, b1 is in the 2^7
   7 -- place while b8 is in the 2^0 place.
   8 data Octet = None | Octet { b1 :: Bit,
   9                             b2 :: Bit,
  10                             b3 :: Bit,
  11                             b4 :: Bit,
  12                             b5 :: Bit,
  13                             b6 :: Bit,
  14                             b7 :: Bit,
  15                             b8 :: Bit }
  16            deriving (Eq)
  17
  18
  19 instance Show Octet where
  20     show Octet.None = "None"
  21     show oct = show (octet_to_int oct)
  22
  23
  24 -- Convert each bit to its integer value, and multiply by the
  25 -- appropriate power of two. Sum them up, and we should get an integer
  26 -- between 0 and 255.
  27 octet_to_int :: Octet -> Int
  28 octet_to_int x =
  29     128 * (bit_to_int (b1 x)) +
  30     64  * (bit_to_int (b2 x)) +
  31     32  * (bit_to_int (b3 x)) +
  32     16  * (bit_to_int (b4 x)) +
  33     8   * (bit_to_int (b5 x)) +
  34     4   * (bit_to_int (b6 x)) +
  35     2   * (bit_to_int (b7 x)) +
  36     1   * (bit_to_int (b8 x))
  37
  38
  39
  40 octet_from_int :: Int -> Octet
  41 octet_from_int x
  42     | (x < 0) || (x > 255) = Octet.None
  43     | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
  44     where
  45       a1 = if (x > 128) then One else Zero
  46       a2 = if ((x `mod` 128) >= 64) then One else Zero
  47       a3 = if ((x `mod` 64)  >= 32) then One else Zero
  48       a4 = if ((x `mod` 32)  >= 16) then One else Zero
  49       a5 = if ((x `mod` 16)  >= 8)  then One else Zero
  50       a6 = if ((x `mod` 8)   >= 4)  then One else Zero
  51       a7 = if ((x `mod` 4)   >= 2)  then One else Zero
  52       a8 = if ((x `mod` 2)   == 1)  then One else Zero
  53
  54
  55 octet_from_string :: String -> Octet
  56 octet_from_string s =
  57     case (reads s :: [(Int, String)]) of
  58       []   -> Octet.None
  59       x:_ -> octet_from_int (fst x)
  60
  61
  62 -- The octet with the least possible value.
  63 min_octet :: Octet
  64 min_octet = Octet Zero Zero Zero Zero Zero Zero Zero Zero
  65
  66
  67 -- The octet with the greatest possible value.
  68 max_octet :: Octet
  69 max_octet = Octet One One One One One One One One