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Newsgroups: comp.lang.c
Subject: Re: Command line globber/tokenizer library for C?
Date: Tue, 17 Sep 2024 22:34:33 -0000 (UTC)
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Michael S <already5chosen@yahoo.com> wrote:
> On Fri, 13 Sep 2024 09:05:04 -0700
> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
> 
>> Michael S <already5chosen@yahoo.com> writes:
>> 
>> [..iterate over words in a string..]
>> 
>> I couldn't resist writing some code along similar lines.  The
>> entry point is words_do(), which returns one on success and
>> zero if the end of string is reached inside double quotes.
>> 
>> 
>> typedef struct gopher_s *Gopher;
>> struct gopher_s { void (*f)( Gopher, const char *, const char * ); };
>> 
>> static  _Bool   collect_word( const char *, const char *, _Bool,
>> Gopher ); static  _Bool   is_space( char );
>> 
>> 
>> _Bool
>> words_do( const char *s, Gopher go ){
>>   char   c      =  *s;
>> 
>>     return
>>       is_space(c)       ?  words_do( s+1, go )
>>   : c                 ?  collect_word( s, s, 1, go )
>> : /***************/    1;
>> }
>> 
>> _Bool
>> collect_word( const char *s, const char *r, _Bool w, Gopher go ){
>>   char   c      =  *s;
>> 
>>     return
>>       c == 0            ?  go->f( go, r, s ),  w
>>   : is_space(c) && w  ?  go->f( go, r, s ),  words_do( s, go )
>> : /***************/    collect_word( s+1, r, w ^ c == '"', go );
>> }
>> 
>> _Bool
>> is_space( char c ){
>>     return  c == ' '  ||  c == '\t';
>> }
> 
>

<snip>
 
> Tested on godbolt.
> gcc -O2 turns it into iteration starting from v.4.4
> clang -O2 turns it into iteration starting from v.4.0
> Latest icc still does not turn it into iteration at least along one
> code paths.
> Latest MSVC implements it as written, 100% recursion.

I tested using gcc 12.  AFAICS calls to 'go->f' in 'collect_word'
are not tail calls and gcc 12 compiles them as normal call.
The other calls are compiled to jumps.  But call to 'collect_word'
in 'words_do' is not "sibicall" and dependig in calling convention
compiler may treat it narmal call.  Two other calls, that is
call to 'words_do' in 'words_do' and call to 'collect_word' in
'collect_word' are clearly tail self recursion and compiler
should always optimize them to a jump.

-- 
                              Waldek Hebisch