On Wed 2019-08-28 21:18:37, Uwe Kleine-König wrote:
> Hello Petr,
>
> On 8/28/19 1:32 PM, Petr Mladek wrote:
> > On Tue 2019-08-27 23:12:44, Uwe Kleine-König wrote:
> >> Petr Mladek had some concerns:
> >>> There are ideas to make the code even more tricky to reduce
> >>> the size, keep it fast.
> >>
> >> I think Enrico Weigelt's suggestion to use a case is the best
> >> performance-wise so that's what I picked up. Also I hope that
> >> performance isn't that important because the need to print an error
> >> should not be so common that it really hurts in production.
This is contadicting. The "best" performance-wise solution was
choosen in favor of space. The next sentence says that performance
is not important.
> > I personally do not like switch/case. It is a lot of code.
> > I wonder if it even saved some space.
>
> I guess we have to die either way. Either it is quick or it is space
> efficient.
I am more concerned about the size. Well, array of strings will
be both fast and size efficient.
> With the big case I trust the compiler to pick something
> sensible expecting that it adapts for example to -Osize.
I am not sure what are the expectations here. I can't imagine
another translation than:
if (val == 1)
str = "EPERM";
else if (val == 2)
str = "ENOENT"
else if (val == 3)
str = "ESRCH"
...
It means that all constans will be hardcoded in the code instead
of in data section. Plus there will be instructions for each
if/else part.
> > If you want to safe space, I would use u16 to store the numbers.
> > Or I would use array of strings. There will be only few holes.
> >
> > You might also consider handling only the most commonly
> > used codes from errno.h and errno-base.h (1..133). There will
> > be no holes and the codes are stable.
>
> I'd like to postpone the discussion about "how" until we agreed about
> the "if at all".
It seems that all people like this feature.
BTW: I though more about generating or cut&pasting the arrary.
I can't find any reasonable way how to generate it.
But both, errno.h and errno-base.h, are super stable. Only
comments were modified or new codes added. Most of them
are defined by POSIX so they should remain stable.
Therefore cut&pasted array of strings looks acceptable.
We should only allow to easily check numbers for each code,
e.g. by defining the array as
const err_str * [] {
"0" /* 0 Success */
"EPERM", /* 1 Operation not permitted */
"ENOENT", /* 2 No such file or directory */
"ESRCH", /* 3 No such process */
...
If there is a hole, we could use something like:
"-41", /* 41 Skipped. EWOULDBLOCK is
defined as EAGAIN. Operation would block */
Best Regards,
Petr
