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SubjectRe: Patch?: linux-2.5.59/sound/soundcore.c referenced non-existant errno variable
On Mon, 20 Jan 2003, Horst von Brand wrote:

[ the war between effeciency and maintainability continues ]

> "Adam J. Richter" <adam@yggdrasil.com> said:
> > To my knowledge, a goto in this case is not necessary for
> > avoiding code duplication. If there are a small number of failable
> > steps that may need to be unwound, you could adopt the style of my patch
> > (which shortened the code slightly):
> >
> > if (step1() == ok) {
> > if (step2() == ok) {
> > if (strep3() == ok)
> > return OK;
> > undo_step2();
> > }
> > undo_step1();
> > }
> > return failure;
>
> The "undo_stepX()"'s pollute the CPU's cache, and (even much worse) the
> gentle reader's.

Given the probably effect of the steps on the cache, I think the
readability argument is a better one, particularly if you have more than a
few steps. There is an effect, but it's relatively small. But use of goto
need not be unreadable.

if (step1() != ok) goto errex0;
if (step2() != ok) goto errex1;
if (step3() == ok) {
if (step4() == ok) return OK;
undo_step3();
}
undo_step2();
errex1:
undo_step1();
errex0:
/* in case there is something other than just return, jump here */
return FAIL;
Less indenting, and the undo's falling through look visually like a switch
without the overhead.

I have not looked at the code this generates, it's a comment on human
readability rather than an actual implementation, and I'm sure someone
will argue that the first failure should just be a return if there's
nothing else which needs to be done. On the other hand the return inline
would be more bytes, so someone else can argue against.

--
bill davidsen <davidsen@tmr.com>
CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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