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, Show)
  17
  18 -- Convert each bit to its integer value, and multiply by the
  19 -- appropriate power of two. Sum them up, and we should get an integer
  20 -- between 0 and 255.
  21 octet_to_int :: Octet -> Int
  22 octet_to_int x =
  23     128 * (bit_to_int (b1 x)) +
  24     64  * (bit_to_int (b2 x)) +
  25     32  * (bit_to_int (b3 x)) +
  26     16  * (bit_to_int (b4 x)) +
  27     8   * (bit_to_int (b5 x)) +
  28     4   * (bit_to_int (b6 x)) +
  29     2   * (bit_to_int (b7 x)) +
  30     1   * (bit_to_int (b8 x))
  31
  32
  33
  34 octet_from_int :: Int -> Octet
  35 octet_from_int x
  36     | (x < 0) || (x > 255) = Octet.None
  37     | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
  38     where
  39       a1 = if (x > 128) then One else Zero
  40       a2 = if ((x `mod` 128) >= 64) then One else Zero
  41       a3 = if ((x `mod` 64)  >= 32) then One else Zero
  42       a4 = if ((x `mod` 32)  >= 16) then One else Zero
  43       a5 = if ((x `mod` 16)  >= 8)  then One else Zero
  44       a6 = if ((x `mod` 8)   >= 4)  then One else Zero
  45       a7 = if ((x `mod` 4)   >= 2)  then One else Zero
  46       a8 = if ((x `mod` 2)   == 1)  then One else Zero
  47
  48
  49 octet_from_string :: String -> Octet
  50 octet_from_string s =
  51     case (reads s :: [(Int, String)]) of
  52       []   -> Octet.None
  53       x:_ -> octet_from_int (fst x)
  54
  55
  56 -- The octet with the least possible value.
  57 min_octet :: Octet
  58 min_octet = Octet Zero Zero Zero Zero Zero Zero Zero Zero
  59
  60
  61 -- The octet with the greatest possible value.
  62 max_octet :: Octet
  63 max_octet = Octet One One One One One One One One