Re: Command line globber/tokenizer library for C?

On Tue, 17 Sep 2024 22:34:33 -0000 (UTC)
antispam@fricas.org wrote:

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.

Naturally.

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.
 

"Should" or not, MSVC does not eliminate them.

The funny thing is that it does eliminate all four calls after I rewrote
the code in more boring style.

_Bool
words_do( const char *s, Gopher go ){
  char   c      =  *s;
#if 1 
  if (is_space(c))
    return  words_do( s+1, go );
  if (c)
    return collect_word( s, s, 1, go );
  return 1;
#else
 return
  is_space(c)       ?  words_do( s+1, go )        :
  c                 ?  collect_word( s, s, 1, go ):
  /***************/    1;
#endif
}

static
_Bool
collect_word( const char *s, const char *r, _Bool w, Gopher go ){
  char   c      =  *s;
#if 1 
  if (c == 0) {
    go->f( go, r, s );
    return  w;
  }
  if (is_space(c) && w) {
    go->f( go, r, s );
    return words_do( s, go );
  }
  return collect_word( s+1, r, w ^ c == '"', go );
#else
 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 );
#endif
}