Re: small example, using complex variables in Ada

[Adam Beneschan <adam@irvine.com>]

On Jun 10, 9:21 am, Colin Paul Gloster <Colin_Paul_Glos...@ACM.org>
wrote:
> On Thu, 10 Jun 2010, Ludovic Brenta sent:
>
> |---------------------------------------------------------------------|
> |"On Jun 10, 5:48 pm, Colin Paul Gloster <Colin_Paul_Glos...@ACM.org> |
> |wrote:                                                               |
> |> On Wed, 9 Jun 2010, Ludovic Brenta sent:                           |
> |>                                                                    |
> |> |     Two_Pi_Over_N : constant := 2 * Pi / N;|                     |
> |>                                                                    |
> |> That is a good suggestion.                                         |
> |>                                                                    |
> |> |"     FOR k in X'range LOOP"                |                     |
> |>                                                                    |
> |> No.                                                                |
> |                                                                     |
> |Why?                                                                 |
> |                                                                     |
> |> |"         FOR m in data'range LOOP          |                     |
> |>                                                                    |
> |> No. Loop down to zero.                                             |
> |                                                                     |
> |Why?"                                                                |
> |---------------------------------------------------------------------|
>
> Though there should be no difference, in reality compilers produce
> less slow machine code when looping down to zero instead of up from
> zero.

I don't think you can state that categorically.  We don't even know
what processor the OP was generating code for.  Not all of them have
"decrement and branch if nonnegative" instructions.  In any event, I
think the only way to really know which one is faster is to try it, or
to examine the generated code---and the latter probably isn't good
enough these days, with all the pipelining that goes on.

                      -- Adam