On Sun, Mar 19, 2006 at 10:26:30PM -0800, Linus Torvalds wrote:
>
>
> On Mon, 20 Mar 2006, Willy Tarreau wrote:
> >
> > Now, does removing the macro completely change the output code ?
> > I think that if something written like this produces the same
> > code, it would be easier to read :
> >
> > #define for_each_cpu_mask(cpu, mask) \
> > for ((cpu) = 0; (cpu) < NR_CPUS; (cpu)++) { \
> > unsigned long __bits = (mask).bits[0] >> (cpu); \
> > if (!__bits) \
> > break; \
> > if (!__bits & 1) \
> > continue; \
> > else
>
> Absolutely, but now it has a dangling "{" that didn't get closed. So the
> above would definitely be more readable, it just doesn't actually work.
>
> Unless you'd do the "end_for_each_cpu" define (to close the statement),
> and update the 300+ places that use this. Which might well be worth it.
>
> So the subtle "break from the middle of a statement expression" was just a
> rather hacky way to avoid having to change all the users of this macro.
>
> Linus
Oh, you're right, now I understand your motivation in doing this.
Then perhaps using your trick but applying it to the whole for loop
would make it easier to read ?
#define for_each_cpu_mask(cpu, mask) \
for ((cpu) = 0; (cpu) < NR_CPUS; (cpu)++) \
({ unsigned long __bits = (mask).bits[0] >> (cpu); \
if (!__bits) \
break; \
if (!__bits & 1) \
continue; \
else \
... \
})
Please note that I've not read the rest of the code, so there
may be some problems left. However, if the above works, I find
it easier to read. And in this case, yes, it's interesting to
be able to break from within an expression.
Cheers,
Willy
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