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[hath.git] / 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 :: Test
77 test_octet_from_int1 =
78 TestCase $ assertEqual "octet_from_int 128 should parse as 10000000" oct1 (octet_from_int 128)
79 where
80 oct1 = Octet One Zero Zero Zero Zero Zero Zero Zero
81
82
83 octet_tests :: [Test]
84 octet_tests = [ test_octet_from_int1 ]