FW: [PATCH][STEP 2] ctype changes for removing locale structures

["Jaap de Wolff" <info at jasoon dot nl>]

-----Oorspronkelijk bericht-----
Van: Jaap de Wolff [mailto:info@jasoon.nl] 
Verzonden: vrijdag 9 februari 2018 18:15
Aan: 'Craig Howland' <howland@LGSInnovations.com>
Onderwerp: RE: [PATCH][STEP 2] ctype changes for removing locale structures



> -----Oorspronkelijk bericht-----
> Van: newlib-owner@sourceware.org [mailto:newlib-owner@sourceware.org]
> Namens Craig Howland
> Verzonden: vrijdag 9 februari 2018 16:51
> Aan: newlib@sourceware.org
> Onderwerp: Re: [PATCH][STEP 2] ctype changes for removing locale 
> structures
> 
> On 02/09/2018 10:06 AM, Jaap de Wolff wrote:
> > modify ctype not to use __locale_ctype_ptr (== __CTYPE_PTR) or 
> > __locale_ctype_ptr_l To do this al inline functions are removed, and 
> > the source implementations test hard coded values of the given 
> > characters
> >
> >
> > ================================== PATCH ================= diff --
> git
> > a/newlib/libc/ctype/isalnum.c b/newlib/libc/ctype/isalnum.c index
> > d926f97b7..6d3864114 100644
> > --- a/newlib/libc/ctype/isalnum.c
> > +++ b/newlib/libc/ctype/isalnum.c
> > @@ -46,5 +46,9 @@ No OS subroutines are required.
> >   int
> >   isalnum (int c)
> >   {
> > +#ifdef _REENT_SMALL
> > +	return (isdigit(c) | islower(c) | isupper(c)); #else
> >   	return(__CTYPE_PTR[c+1] & (_U|_L|_N));
> > +#endif
> >   }
> I would think that we should be able to do better than this, as this 
> method is taking a half step backwards for some of the functions, such 
> as isalnum().  That is, it potentially loses the efficiency of doing 
> one table lookup plus one OR, as it needs to do N table lookups and 
> N+N-1 ORs (where N appears to be from 1-3).  I say "potentially" 
> because maybe the compiler would end up reducing it to the
> 1+1 case, but maybe not, too (depending on compiler, compiler 
> 1+settings). Before
> locale was added, isalnum(), for example, was
> 
> return(__ctype_ptr__[c+1] & (_U|_L));
> 
> I'm not sure what the right thing is now (still __ctype_ptr__?), but 
> the same basic thing ought to work, knowing the right thing to put in.  
> But for that matter, why not in the REENT_SMALL case simply redefine 
> __CTYPE_PTR to point to the right thing?  Then all these other source 
> file changes become unnecessary. It seems reasonable to expect this to 
> work, and it would be a cleaner solution (since the is*.c files remain 
> untouched, without #ifs).  The stated purpose of the patch is to stop 
> ctype from using __locale_ctype_ptr, but ctype.h is where it is defined to be __CTYPE_PTR--so just define it differently.
> 
> Craig

Craig,
In basic the intention of my patches is to make to memory footprint for embedded environment small.
I talked about locale, and a part of the locale definition is a lookup table with the characteristics of each character.
Of course it is possible to move the lookup table outside the locale, but then the lookup table still takes 257 bytes of memory.

In the beginning my intention was just to move the __global_locale table from ram to rom, and a reaction was that that was not enough when using embedded processors with 2K or even 1K of ROM and 128 bytes of RAM.

I do think that for the intended users of the REENT_SMALL computation speed (efficiency) is less important as memory.
So I replaces all usage of a lookup table by a (kind of) computation.

Jaap