Re: sub-optimal code for packed boolean arrays -- bug or inherent limitation

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

"Jeffrey R. Carter" <spam.jrcarter.not@acm.nospam.org> writes:

> You should also be aware that you're sending the compiler conflicting
> messages. Packing the array indicates that you want the compiler to
> minimize storage, even at the expense of speed,...

Well, sort of.  Pack means to minimize storage even at the (possible)
expense of speed of accessing the components.  Speed overall can be
improved by packing.  For example, speed of copying and comparing the
whole packed object, and passing it around as parameters, will typically
be improved by packing.

And of course using less memory will typically improve cache and paging
performance.

So on a desktop computer with "plenty" of memory, packing is mainly used
to improve speed -- there's no "time/space" tradeoff.  A small embedded
system might have such tradeoffs.

>... while "pragma Optimize
> (Time);" indicates that you want to minimize time, even at the expense
> of storage. Obtaining speed often requires wasting storage; the fastest
                              ^^^^^

I'd say, "sometimes", nor "often".  Usually, wasting storage means
wasting time.

> implementation might be to not pack the array. I don't know how many of
> these you have, but with the large memories on modern machines, you
> might be better off with the additional 56 bytes per array. Again, you
> won't know for sure until you have a working version you can measure.

Measurement is a Good Thing.

- Bob