Add machine words and instructions

src/Mima/Word.hs

@@ -0,0 +1,36 @@
+module Mima.Word where
+
+import           Data.Bits
+import           Data.Word
+
+import           Mima.Util
+
+class Word32Based t where
+  fromWord32 :: Word32 -> t
+  toWord32 :: t -> Word32
+
+-- The MiMa's words are 24 bits long. The smallest word they fit in is
+-- 'Word32'.
+
+newtype MimaWord = MimaWord Word32
+  deriving (Show, Eq)
+
+instance ToText MimaWord where
+  toText (MimaWord w) = toHex 6 w
+
+instance Word32Based MimaWord where
+  fromWord32 w = MimaWord $ w .&. 0x00FFFFFF
+  toWord32 (MimaWord w) = w
+
+-- The MiMa's addresses are 20 bits long. The smallest word they fit
+-- in is 'Word32'.
+
+newtype MimaAddress = MimaAddress Word32
+  deriving (Show, Eq)
+
+instance ToText MimaAddress where
+  toText (MimaAddress w) = toHex 5 w
+
+instance Word32Based MimaAddress where
+  fromWord32 w = MimaAddress $ w .&. 0x000FFFFF
+  toWord32 (MimaAddress w) = w