17. Word

This library provides unsigned integers of various sizes. The types supported are as follows:

type number of bits Word8 8 Word16 16 Word32 32 Word64 64

For each type W above, we provide the following functions and instances. The type I refers to the signed integer type of the same size.

data W            -- Unsigned Ints
instance Eq       W
instance Ord      W
instance Show     W
instance Read     W
instance Bounded  W
instance Num      W
instance Real     W
instance Integral W
instance Enum     W
instance Ix       W
instance Bits     W

word8ToWord16  :: Word8   -> Word16
word8ToWord32  :: Word8   -> Word32
word8ToWord64  :: Word8   -> Word64

word16ToWord8   :: Word16  -> Word8
word16ToWord32  :: Word16  -> Word32
word16ToWord64  :: Word16  -> Word64

word32ToWord8  :: Word32 -> Word8
word32ToWord16 :: Word32 -> Word16
word32ToWord64 :: Word32 -> Word64

word64ToWord8  :: Word64 -> Word8
word64ToWord16 :: Word64 -> Word16
word64ToWord32 :: Word64 -> Word32

word8ToInt     :: Word8  -> Int
word16ToInt    :: Word16 -> Int
word32ToInt    :: Word32 -> Int
word64ToInt    :: Word64 -> Int

intToWord8     :: Int    -> Word8
intToWord16    :: Int    -> Word16
intToWord32    :: Int    -> Word32
intToWord64    :: Int    -> Word64

word64ToInteger :: Word64  -> Integer
integerToWord64 :: Integer -> Word64

Notes:

• All arithmetic is performed modulo 2^n One non-obvious consequence of this is that negate should not raise an error on negative arguments.
• The coercion wToI converts an unsigned n-bit value to the signed n-bit value with the same representation. For example, word8ToInt8 0xff = -1. Likewise, iToW converts signed n-bit values to the corresponding unsigned n-bit value.
• Use Prelude.fromIntegral :: (Integral a, Num b) => a -> b to coerce between different sizes or to preserve sign when converting between values of the same size.
• It would be very natural to add a type a type Natural providing an unbounded size unsigned integer --- just as Integer provides unbounded size signed integers. We do not do that yet since there is no demand for it. Doing so would require Bits.bitSize to return Maybe Int.
• The rules that hold for Enum instances over a bounded type such as Int (see the section of the Haskell report dealing with arithmetic sequences) also hold for the Enum instances over the various Word types defined here.

Implementation notes:

• Hugs only provides Eq, Ord, Read and Show instances for Word64 at the moment.