src/Octet.hs

   1 module Octet where
   2
   3 import Test.HUnit
   4
   5 import Bit
   6
   7 -- An Octet consists of eight bits. For our purposes, the most
   8 -- significant bit will come "first." That is, b1 is in the 2^7
   9 -- place while b8 is in the 2^0 place.
  10 data Octet = None | Octet { b1 :: Bit,
  11                             b2 :: Bit,
  12                             b3 :: Bit,
  13                             b4 :: Bit,
  14                             b5 :: Bit,
  15                             b6 :: Bit,
  16                             b7 :: Bit,
  17                             b8 :: Bit }
  18            deriving (Eq)
  19
  20
  21 instance Show Octet where
  22     show Octet.None = "None"
  23     show oct = show (octet_to_int oct)
  24
  25
  26 -- Convert each bit to its integer value, and multiply by the
  27 -- appropriate power of two. Sum them up, and we should get an integer
  28 -- between 0 and 255.
  29 octet_to_int :: Octet -> Int
  30 octet_to_int x =
  31     128 * (bit_to_int (b1 x)) +
  32     64  * (bit_to_int (b2 x)) +
  33     32  * (bit_to_int (b3 x)) +
  34     16  * (bit_to_int (b4 x)) +
  35     8   * (bit_to_int (b5 x)) +
  36     4   * (bit_to_int (b6 x)) +
  37     2   * (bit_to_int (b7 x)) +
  38     1   * (bit_to_int (b8 x))
  39
  40
  41
  42 octet_from_int :: Int -> Octet
  43 octet_from_int x
  44     | (x < 0) || (x > 255) = Octet.None
  45     | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
  46     where
  47       a1 = if (x >= 128) then One else Zero
  48       a2 = if ((x `mod` 128) >= 64) then One else Zero
  49       a3 = if ((x `mod` 64)  >= 32) then One else Zero
  50       a4 = if ((x `mod` 32)  >= 16) then One else Zero
  51       a5 = if ((x `mod` 16)  >= 8)  then One else Zero
  52       a6 = if ((x `mod` 8)   >= 4)  then One else Zero
  53       a7 = if ((x `mod` 4)   >= 2)  then One else Zero
  54       a8 = if ((x `mod` 2)   == 1)  then One else Zero
  55
  56
  57 octet_from_string :: String -> Octet
  58 octet_from_string s =
  59     case (reads s :: [(Int, String)]) of
  60       []   -> Octet.None
  61       x:_ -> octet_from_int (fst x)
  62
  63
  64 -- The octet with the least possible value.
  65 min_octet :: Octet
  66 min_octet = Octet Zero Zero Zero Zero Zero Zero Zero Zero
  67
  68
  69 -- The octet with the greatest possible value.
  70 max_octet :: Octet
  71 max_octet = Octet One One One One One One One One
  72
  73
  74
  75 -- HUnit Tests
  76 test_octet_from_int1 =
  77     TestCase $ assertEqual "octet_from_int 128 should parse as 10000000" oct1 (octet_from_int 128)
  78     where
  79       oct1 = Octet One Zero Zero Zero Zero Zero Zero Zero
  80
  81
  82 octet_tests = [ test_octet_from_int1 ]