Re: 16bit ctype table

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Tue, Aug 21, 2012 at 01:01:14AM +0900, Takehiko NOZAKI wrote:
> > My point is that we need to keep both tables until the major bump.
> > Minimising the differences between them keeps the runtime impact as
> > small as possible. I am all for reducing the difference further, but
> > until the major bump, the old table won't go away.
> 
> to clarify difference:
> 
> fundamentally, your patch and mine is not so differ.
>   * both libc.so.12 should have 8bit old ctype table and 16bit new ctype table
>   * both libc.so.13 have only 16bit new ctype table.
> so that aparently there is *no* diffrence libc's size impact.
> 
> *only* diffrence is 16bit bitmask pattern.
> 
> 1. _CTYPE_* is not same layout with _RUNETYPE_*, keep old layout (by joerg)
>   * partial source code compatibility.
>   * complex rune table -> ctype table conversion, by bogus 
> _runetype_to_ctype().
> 
> 2. _CTYPE_*  is same layout with _RUNETYPE_* (by tnozaki)
>   * simple rune table -> ctype table conversion,  (_CTYPE_A << 8) == 
> _RUNETYPE_A
>   * no source code compatibiliy.

Agreed.

> in my opinion again:
> 
> 1. source code compatibility
> in this case, it is not important, because _CTYPE_* is completely
> *private* macro.
> there's someone(such as libstdc++) use it and took an arrow in his
> knee, i don't mind.
> 
> if you don't agree with me, why you  do following change? ;)
> http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/sys/ctype_bits.h.diff?r1=1.1&r2=1.2

Note that this is about both API and ABI compatibility. I don't care too
much about the API as long as code breaks if the semantics change. But:
we have to preserve the ABI at least for the old table, since that's
what all users of ctype.h compiled against the old version depend on.

> 2. rune table -> ctype table conversion
> simple conversion is good for reading, maintanance, and our health.
> especially peformance, POSIX2008's multi-locale wants low-latency LC_CTYPE.

I agree on that as well. Basically, I don't think switching to a
different _CTYPE_* mask set helps us as long as we keep the old layout
around as well. So the only real question is whether we bit bullet now
or later. I'm more inclined to add this to the list of things that can
be cleaned up for libc.so.13.

Joerg