1 {-# OPTIONS_GHC -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
5 -- Copyright : (c) The University of Glasgow 2001
6 -- License : BSD-style (see the file libraries/base/LICENSE)
8 -- Maintainer : libraries@haskell.org
9 -- Stability : experimental
10 -- Portability : portable
12 -- Unsigned integer types.
14 -----------------------------------------------------------------------------
18 -- * Unsigned integral types
21 Word8, Word16, Word32, Word64,
28 #ifdef __GLASGOW_HASKELL__
37 import NHC.FFI (Word8, Word16, Word32, Word64)
38 import NHC.SizedTypes (Word8, Word16, Word32, Word64) -- instances of Bits
44 * All arithmetic is performed modulo 2^n, where n is the number of
45 bits in the type. One non-obvious consequence of this is that 'Prelude.negate'
46 should /not/ raise an error on negative arguments.
48 * For coercing between any two integer types, use
49 'Prelude.fromIntegral', which is specialized for all the
50 common cases so should be fast enough. Coercing word types to and
51 from integer types preserves representation, not sign.
53 * It would be very natural to add a type @Natural@ providing an unbounded
54 size unsigned integer, just as 'Prelude.Integer' provides unbounded
55 size signed integers. We do not do that yet since there is no demand
58 * The rules that hold for 'Prelude.Enum' instances over a bounded type
59 such as 'Prelude.Int' (see the section of the Haskell report dealing
60 with arithmetic sequences) also hold for the 'Prelude.Enum' instances
61 over the various 'Word' types defined here.
63 * Right and left shifts by amounts greater than or equal to the width
64 of the type result in a zero result. This is contrary to the
65 behaviour in C, which is undefined; a common interpretation is to
66 truncate the shift count to the width of the type, for example @1 \<\<
67 32 == 1@ in some C implementations.