Re: Clear entire field vs substring

On Mon, May 21, 2012 at 5:28 PM, Albert York <alfromme@xxxxxxxxx> wrote:

Assuming there is a reason I have to clear the data before starting,

This is a big (and I would guess rather crazy) assumption. If you
happen to be able to describe a situation where this is the case, I
would be interested to hear it.

which is faster:

workfield = *blanks

or

%substr(workfield:1:len) = *blanks

Well, %substr doesn't work at all, but maybe you mean %subst. ;)

The answer is that on a model 810 running V5R2, blanking out a small
substring is faster than clearing the entire field of 2000 bytes,
potentially several times faster, if you are clearing only a tiny
portion of the field. I don't know the underlying low-level code, I
just wrote a simple-minded RPG program to try various things.

I cannot stress enough, though, that I don't know a legitimate use
case for explicitly pre-clearing a field. And I still recommend human
source readability over micro-optimization. (Otherwise, why aren't we
all programming in assembly? Or lower?)

If you do not explicitly pre-clear the field, you have the best of all
worlds - fastest (because no-op is faster than any op) and clearest
source code (zero lines of superfluous code is easier to write, read,
and maintain than some positive number of lines of superfluous code).

John