1 {-# LANGUAGE CPP, NoImplicitPrelude #-}
3 -----------------------------------------------------------------------------
6 -- Copyright : (c) The University of Glasgow 2001
7 -- License : BSD-style (see the file libraries/base/LICENSE)
9 -- Maintainer : libraries@haskell.org
10 -- Stability : experimental
11 -- Portability : portable
13 -- Unsigned integer types.
15 -----------------------------------------------------------------------------
19 -- * Unsigned integral types
22 Word8, Word16, Word32, Word64,
29 #ifdef __GLASGOW_HASKELL__
38 import NHC.FFI (Word8, Word16, Word32, Word64)
39 import NHC.SizedTypes (Word8, Word16, Word32, Word64) -- instances of Bits
45 * All arithmetic is performed modulo 2^n, where n is the number of
46 bits in the type. One non-obvious consequence of this is that 'Prelude.negate'
47 should /not/ raise an error on negative arguments.
49 * For coercing between any two integer types, use
50 'Prelude.fromIntegral', which is specialized for all the
51 common cases so should be fast enough. Coercing word types to and
52 from integer types preserves representation, not sign.
54 * It would be very natural to add a type @Natural@ providing an unbounded
55 size unsigned integer, just as 'Prelude.Integer' provides unbounded
56 size signed integers. We do not do that yet since there is no demand
59 * The rules that hold for 'Prelude.Enum' instances over a bounded type
60 such as 'Prelude.Int' (see the section of the Haskell report dealing
61 with arithmetic sequences) also hold for the 'Prelude.Enum' instances
62 over the various 'Word' types defined here.
64 * Right and left shifts by amounts greater than or equal to the width
65 of the type result in a zero result. This is contrary to the
66 behaviour in C, which is undefined; a common interpretation is to
67 truncate the shift count to the width of the type, for example @1 \<\<
68 32 == 1@ in some C implementations.