1 {-# LANGUAGE Safe #-}

2 {-# LANGUAGE CPP, NoImplicitPrelude #-}

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 -----------------------------------------------------------------------------

19 (

20 -- * Unsigned integral types

22 Word,

25 -- * Notes

27 -- $notes

30 #ifdef __GLASGOW_HASKELL__

32 #endif

34 #ifdef __HUGS__

36 #endif

38 #ifdef __NHC__

42 #endif

44 {- $notes

46 * All arithmetic is performed modulo 2^n, where n is the number of

47 bits in the type. One non-obvious consequence of this is that 'Prelude.negate'

48 should /not/ raise an error on negative arguments.

50 * For coercing between any two integer types, use

51 'Prelude.fromIntegral', which is specialized for all the

52 common cases so should be fast enough. Coercing word types to and

53 from integer types preserves representation, not sign.

55 * It would be very natural to add a type @Natural@ providing an unbounded

56 size unsigned integer, just as 'Prelude.Integer' provides unbounded

57 size signed integers. We do not do that yet since there is no demand

58 for it.

60 * The rules that hold for 'Prelude.Enum' instances over a bounded type

61 such as 'Prelude.Int' (see the section of the Haskell report dealing

62 with arithmetic sequences) also hold for the 'Prelude.Enum' instances

63 over the various 'Word' types defined here.

65 * Right and left shifts by amounts greater than or equal to the width

66 of the type result in a zero result. This is contrary to the

67 behaviour in C, which is undefined; a common interpretation is to

68 truncate the shift count to the width of the type, for example @1 \<\<

69 32 == 1@ in some C implementations.

70 -}