Re: Efficiency of code generated by Ada compilers

[Robert A Duff <bobduff@shell01.TheWorld.com>]

csampson@inetworld.net (Charles H. Sampson) writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> wrote:
>
>      I'm surprised, Bob.  Are you saying that you signed integers in
> preference to a modular type for a variable that cycles?

Yes.  Unless I'm forced to use modular for some other reason
(e.g. I need one extra bit).

>...I use
> modular-typed variables and, if I've got my engineer's hat on, write
>
>      I := I + 1;  -- Modular variable.  Wraps.

You're not alone.  Even Tucker has advocated using modular
types for this sort of thing.

But I think an explicit "mod N" is clearer than a comment.

Variables that cycle are rare, so should be noted explicitly
in the code.  And, as Dmitry noted, modular types only work
when the lower bound is 0.  It's not unreasonable to have
a circular buffer indexed by a range 1..N.

See my point?  Still "surprised"?

> but I have to admit that in the heat of battle the comment might be
> omitted.  Even in that case, the variable name probably indicates that
> wrapping should be expected.

- Bob

P.S. Can anybody recall the definition of "not" on modular
types, when the modulus is not a power of 2, without
looking it up?  Hint: It makes no sense.  The only feature
that's worse than "modular types" is "modular types with a
non-power-of-2 modulus".  ;-)