Re: Reversing Array Elements?

glen herrmannsfeldt <gah@xxxxxxxxxxxxxxxx> wrote:

steve <kargls@xxxxxxxxxxx> wrote:

< So, for the pointer p, the compiler sets up a dope vector
< and 'points' the first element of p at the last element of
< a.

So it doesn't actually reverse the array.

Depends what you mean by "actually reverse the array". It is an array.
It has the elements in reverse order. It doesn't force making a copy of
the array stored in a reverse memory layout; I assume that's what you
mean by "actually reverse the array".

That is a fairly low-level implementation-oriented view (not surprising)
rather than a specification of the language. The language specification
is deliberately more abstract than that. As a result, it gets hard to
absolutely guarantee much of anything at that level. The best one can do
is describe typical or easy implementations. An implementation certainly
could make such a reordered copy in physical memory as an optimization.
In fact, if you pass such an array as an actual argument to an
explicit-shape or assumed-size dummy, it very likely would result in a
copy reordered in physical memory. So would assignment.

While I'm no expert (at al) on IDL, I'd guess that the same was true
there - that you don't have a guarantee that the operation in question
causes a physically reversed copy in memory.

And for that most part, I'd guess that one would not and should not
care. There are legitimate questions relating to performance. But that's
a separate question from the one of whether the language defines the
operation. See Michael's comment:

but I have no idea how (in)effecient that is.

--
Richard Maine | Good judgment comes from experience;
email: last name at domain . net | experience comes from bad judgment.
domain: summertriangle | -- Mark Twain
.

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