Re: efficient vector/matrix operations in Ada

[18k11tm001@sneakemail.com (Russ)]

Larry Hazel <lhazel@mindspring.com> wrote in message news:<3B783732.A3A1EB82@mindspring.com>...
> Russ wrote:
> > 
> > Here's how you write "A = B + C + D;" efficiently:
> > 
> >     A  = B;
> >     A += C;
> >     A += D;
> > 
> > This requires no temporary matrices or passing by value. The original
> > form (A=B+C+D) is fine for rapid prototyping, but the efficient form
> > is preferable for production code. As far as I am concerned, Ada
> > really needs arithmetic assignment operators. Sure, you can use
> > procedures, but they're intent and effect is not as obvious to the
> > reader.
> > 
> Seems to me if a compiler can't generate the most efficient code for 
> 
> A = B + C + D
> 
>   or
> 
> A := B + C + D
> 
> in any language, you need a different compiler.
> 
> Larry

I'm no compiler expert, but I seriously doubt that you are correct
here. Come to think of it, I'll just say that you are flat out
wrong--and I'll eat crow if you are right. The difference (in C++)
between

    A = B + C + D;
and
    A = B; A += C; A += D;

is more fundamental than a compiler can account for. Don't forget that
"+" and "+=" are user-defined operators to start with. The former says
to add B, C, and D, place the result in a temporary matrix, and copy
that matrix by value back into A. The latter says to copy B into A,
Add C directly to the result, then add D directly to that result. The
latter needs no temporary matrices, whereas the former requires a
temporary for each "+" operator. A special preprocessor could possibly
convert the former to the latter, but I don't see how a compiler could
possibly do it.

This is all old hat in the C++ community. Ada is a great language, but
it missed the boat here. If you don't believe it, you probably don't
understand efficient vector/matrix operations.

By the way, if you think the arithmetic operators should be called
"+:=", "-:=", etc., I give up.

Russ