src/Octet.hs

   1 module Octet where
   2
   3 import Test.HUnit
   4 import Test.QuickCheck
   5
   6 import Bit
   7
   8 -- An Octet consists of eight bits. For our purposes, the most
   9 -- significant bit will come "first." That is, b1 is in the 2^7
  10 -- place while b8 is in the 2^0 place.
  11 data Octet = None | Octet { b1 :: Bit,
  12                             b2 :: Bit,
  13                             b3 :: Bit,
  14                             b4 :: Bit,
  15                             b5 :: Bit,
  16                             b6 :: Bit,
  17                             b7 :: Bit,
  18                             b8 :: Bit }
  19            deriving (Eq)
  20
  21
  22 instance Show Octet where
  23     show Octet.None = "None"
  24     show oct = show (octet_to_int oct)
  25
  26
  27 instance Arbitrary Octet where
  28     arbitrary = do
  29       a1 <- arbitrary :: Gen Bit
  30       a2 <- arbitrary :: Gen Bit
  31       a3 <- arbitrary :: Gen Bit
  32       a4 <- arbitrary :: Gen Bit
  33       a5 <- arbitrary :: Gen Bit
  34       a6 <- arbitrary :: Gen Bit
  35       a7 <- arbitrary :: Gen Bit
  36       a8 <- arbitrary :: Gen Bit
  37       return (Octet a1 a2 a3 a4 a5 a6 a7 a8)
  38
  39     coarbitrary _ = variant 0
  40
  41
  42 -- Convert each bit to its integer value, and multiply by the
  43 -- appropriate power of two. Sum them up, and we should get an integer
  44 -- between 0 and 255.
  45 octet_to_int :: Octet -> Int
  46 octet_to_int x =
  47     128 * (bit_to_int (b1 x)) +
  48     64  * (bit_to_int (b2 x)) +
  49     32  * (bit_to_int (b3 x)) +
  50     16  * (bit_to_int (b4 x)) +
  51     8   * (bit_to_int (b5 x)) +
  52     4   * (bit_to_int (b6 x)) +
  53     2   * (bit_to_int (b7 x)) +
  54     1   * (bit_to_int (b8 x))
  55
  56
  57
  58 octet_from_int :: Int -> Octet
  59 octet_from_int x
  60     | (x < 0) || (x > 255) = Octet.None
  61     | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
  62     where
  63       a1 = if (x >= 128) then One else Zero
  64       a2 = if ((x `mod` 128) >= 64) then One else Zero
  65       a3 = if ((x `mod` 64)  >= 32) then One else Zero
  66       a4 = if ((x `mod` 32)  >= 16) then One else Zero
  67       a5 = if ((x `mod` 16)  >= 8)  then One else Zero
  68       a6 = if ((x `mod` 8)   >= 4)  then One else Zero
  69       a7 = if ((x `mod` 4)   >= 2)  then One else Zero
  70       a8 = if ((x `mod` 2)   == 1)  then One else Zero
  71
  72
  73 octet_from_string :: String -> Octet
  74 octet_from_string s =
  75     case (reads s :: [(Int, String)]) of
  76       []   -> Octet.None
  77       x:_ -> octet_from_int (fst x)
  78
  79
  80 -- The octet with the least possible value.
  81 min_octet :: Octet
  82 min_octet = Octet Zero Zero Zero Zero Zero Zero Zero Zero
  83
  84
  85 -- The octet with the greatest possible value.
  86 max_octet :: Octet
  87 max_octet = Octet One One One One One One One One
  88
  89
  90
  91 -- HUnit Tests
  92 test_octet_from_int1 :: Test
  93 test_octet_from_int1 =
  94     TestCase $ assertEqual "octet_from_int 128 should parse as 10000000" oct1 (octet_from_int 128)
  95     where
  96       oct1 = Octet One Zero Zero Zero Zero Zero Zero Zero
  97
  98
  99 octet_tests :: [Test]
 100 octet_tests = [ test_octet_from_int1 ]