Re: New Book: The School of Niklaus Wirth

| >There are two reasons for wanting an unsigned type:
| >
| > - To extend the range of small integers....
| > - To implement "modulo arithmetic"....
|
| The trouble with just using a subtype for unsigned arithmetic is that
| you lose one bit....


Arithmetic on a subrange, to make any sense, is the same as arithmetic
on the super-range, with results restricted to the subrange. You
can't get modulo-2^k arithmetic this way if you didn't have it to
begin with - and signed arithmetic is *not* modulo-2^k arithmetic.


If you want modulo arithmetic operators, you need to explicitly put
them into the language. Whether you put them in on their own, or make
up a whole type to go along with them, is a design choice.
-- Jerry
[Someone else noted that unsigned types can also be useful to map onto
hardware registers where the contents aren't signed numbers. But I do
agree that the best way to implement modular arithmetic is as modular
arithmetic, not as a somewhat obscure side-effect of the type system.
-John]

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