8af39b6d4d196cfaaa30c08dfefe3fa5c2ef13e4
[ghc.git] / libraries / base / Data / Word.hs
1 {-# LANGUAGE Safe #-}
2 {-# LANGUAGE NoImplicitPrelude #-}
3
4 -----------------------------------------------------------------------------
5 -- |
6 -- Module : Data.Word
7 -- Copyright : (c) The University of Glasgow 2001
8 -- License : BSD-style (see the file libraries/base/LICENSE)
9 --
10 -- Maintainer : libraries@haskell.org
11 -- Stability : experimental
12 -- Portability : portable
13 --
14 -- Unsigned integer types.
15 --
16 -----------------------------------------------------------------------------
17
18 module Data.Word
19 (
20 -- * Unsigned integral types
21
22 Word,
23 Word8, Word16, Word32, Word64,
24
25 -- * byte swapping
26 byteSwap16, byteSwap32, byteSwap64,
27
28 -- * Notes
29
30 -- $notes
31 ) where
32
33 import GHC.Word
34
35 {- $notes
36
37 * All arithmetic is performed modulo 2^n, where n is the number of
38 bits in the type. One non-obvious consequence of this is that 'Prelude.negate'
39 should /not/ raise an error on negative arguments.
40
41 * For coercing between any two integer types, use
42 'Prelude.fromIntegral', which is specialized for all the
43 common cases so should be fast enough. Coercing word types to and
44 from integer types preserves representation, not sign.
45
46 * It would be very natural to add a type @Natural@ providing an unbounded
47 size unsigned integer, just as 'Prelude.Integer' provides unbounded
48 size signed integers. We do not do that yet since there is no demand
49 for it.
50
51 * The rules that hold for 'Prelude.Enum' instances over a bounded type
52 such as 'Prelude.Int' (see the section of the Haskell report dealing
53 with arithmetic sequences) also hold for the 'Prelude.Enum' instances
54 over the various 'Word' types defined here.
55
56 * Right and left shifts by amounts greater than or equal to the width
57 of the type result in a zero result. This is contrary to the
58 behaviour in C, which is undefined; a common interpretation is to
59 truncate the shift count to the width of the type, for example @1 \<\<
60 32 == 1@ in some C implementations.
61 -}
62