Add a None constructor for Octets.

[hath.git] / src / Octet.hs

diff --git a/src/Octet.hs b/src/Octet.hs
index 28d3d7d5feb3b8e4165122ea2e689c5b1bf6e1e5..e0a4bf655c1ece922a37d5fcdc8f2634957a1a3d 100644 (file)
--- a/src/Octet.hs
+++ b/src/Octet.hs
@@ -5,14 +5,14 @@ import Bit
 -- An Octet consists of eight bits. For our purposes, the most
 -- significant bit will come "first." That is, b1 is in the 2^7
 -- place while b8 is in the 2^0 place.
-data Octet = Octet { b1 :: Bit,
-                     b2 :: Bit,
-                     b3 :: Bit,
-                     b4 :: Bit,
-                     b5 :: Bit,
-                     b6 :: Bit,
-                     b7 :: Bit,
-                     b8 :: Bit }
+data Octet = None | Octet { b1 :: Bit,
+                            b2 :: Bit,
+                            b3 :: Bit,
+                            b4 :: Bit,
+                            b5 :: Bit,
+                            b6 :: Bit,
+                            b7 :: Bit,
+                            b8 :: Bit }
            deriving (Eq, Show)
 
 -- Convert each bit to its integer value, and multiply by the
@@ -30,6 +30,22 @@ octet_to_int x =
     0   * (bit_to_int (b8 x))
 
 
+
+octet_from_int :: Int -> Octet
+octet_from_int x
+    | (x < 0) || (x > 255) = Octet.None
+    | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
+    where
+      a1 = if (x `mod` 128) > 0 then One else Zero
+      a2 = if (x `mod` 64)  > 0 then One else Zero
+      a3 = if (x `mod` 32)  > 0 then One else Zero           
+      a4 = if (x `mod` 16)  > 0 then One else Zero
+      a5 = if (x `mod` 8)   > 0 then One else Zero
+      a6 = if (x `mod` 4)   > 0 then One else Zero
+      a7 = if (x `mod` 2)   > 0 then One else Zero           
+      a8 = if (x `mod` 1)   > 0 then One else Zero
+
+
 -- The octet with the least possible value.
 min_octet :: Octet
 min_octet = Octet Zero Zero Zero Zero Zero Zero Zero Zero