Re: the most optimal string "trim" implementation

[Sean Conner <sean@...>]

It was thus said that the Great David Manura once stated:
> On Sat, Dec 26, 2009 at 6:31 PM, Shmuel Zeigerman wrote:
> > [this] slightly outperformed your variant, except for the all-space strings,
> > where it performed worse (which I don't understand why).
> > function trim(s)
> >  local from = s:find("%S")
> >  return from and s:match(".*%S", from) or ""
> > end
> 
> This variant of yours performs much better in the worst case and has
> about the same performance overall as my last one:
> 
> function trim(s)
>   local from = s:match"^%s*()"
>   return from > #s and "" or s:match(".*%S", from)
> end
> 
> For some reason, s:find"^%s*$" is about twice as fast as s:find"%S"
> given s = (" "):rep(100).

  I guess the following would be considered "cheating" then?

#include <stddef.h>
#include <ctype.h>
#include <lua.h>

int trim(lua_State *L)
{
  const char *front;
  const char *end;
  size_t      size;
  
  front = lua_tolstring(L,1,&size);
  end   = &front[size - 1];
  
  lua_pop(L,1);
  
  for ( ; size && isspace(*front) ; size-- , front++)
    ;  
  for ( ; size && isspace(*end) ; size-- , end--)
    ;

  lua_pushlstring(L,front,(size_t)(end - front) + 1);
  return 1;
}

int luaopen_trim(lua_State *L)
{
  lua_register(L,"trim",trim);
  return 0;
}

  -spc (Compile into shared object, load using "require" ... )