Re: New Book: The School of Niklaus Wirth

Jerry Leichter <jerrold.leichter@smarts.com> writes:


>There are two reasons for wanting an unsigned type:
>
> - To extend the range of small integers. This was very
> important in the days of 16-bit ints, and is almost
> certainly why unsigned ints were originally added
> to C. With 32 and now 64 bit ints the standard
> these days, this is rarely of any significance.
>
> - To implement "modulo arithmetic". Unsigned ints typically
> (and, by standard in C/C++) the mathematical properties
> of arithmetic mod 2^k. There are times when this is
> useful.


The trouble with just using a subtype for unsigned arithmetic is that
you lose one bit. Many of the most important uses of modulo
arithmetic are for the case where `k' is the word size. If your
language only provides 32-bit signed ints and subtypes thereof, and
you need 32-bit unsigned ints, then you're out of luck.


--
Fergus Henderson <fjh@cs.mu.oz.au> | "I have always known that the pursuit
                                                                        | of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.

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