Re: Concatenating strings with '+'

[Chris Marrin <chris@...>]

Ignacio Burgueño wrote:
> > -----Original Message-----
> > From: lua-bounces@bazar2.conectiva.com.br 
> > [mailto:lua-bounces@bazar2.conectiva.com.br] On Behalf Of Chris Marrin
> > Sent: Wednesday, July 20, 2005 6:39 PM
> > To: Lua list
> > Subject: Re: Concatenating strings with '+'
> >
> > Ben Sunshine-Hill wrote:
> >
> > > On 7/20/05, Ignacio Burgueño <ignacio@tecnolink.com.uy> wrote:
> >
> > Adding this logic to Lua would be very easy. You would simply 
> > go into lvm.c and change the Arith() function to test for 
> > strings if op is TM_ADD and then jump out to luaV_concat() if 
> > so. This adds a bit of logic to Arith() which slows down 
> > every arithmetic operation. But, at worst, this is something like:
> >
> >     if (op == TM_ADD &&
> >             (ttype(rb) == LUA_TSTRING || ttype(rc) == LUA_TSTRING))
> >         luaV_concat(...);
> >
> > For all ops other than ADD this adds one integer compare and 
> > for ADD it adds an additional one or two integer compares. 
> > Not bad for what it gives you IMHO...
>
>
> Since I don't know the Lua internals quite well, I'm not sure if this code
> is OK.
> I modified the luaV_execute function in lvm.c. Do you see anything obviously
> wrong in it?
> Thanks in advance
>
> case OP_ADD: {
>         TObject *rb = RKB(i);
>         TObject *rc = RKC(i);
>         if (ttisnumber(rb) && ttisnumber(rc)) {
>           setnvalue(ra, nvalue(rb) + nvalue(rc));
>         }
> /* agregado por mi => inicio (para que pueda concatenar strings con '+' */
> 		else if(ttisstring(rb) && ttisstring(rc)) {
> 			char *buffer;
> 			int iLen1 = tsvalue(rb)->tsv.len;
> 			int iLen2 = tsvalue(rc)->tsv.len;
> 			if ((iLen1 + iLen2) > MAX_SIZET) luaG_runerror(L,
> "string size overflow");
> 			buffer = luaZ_openspace(L, &G(L)->buff, iLen1 +
> iLen2);
> 			memcpy(buffer, svalue(rb), iLen1);
> 			memcpy(buffer + iLen1, svalue(rc), iLen2);
> 			setsvalue2s(ra, luaS_newlstr(L, buffer, iLen1 +
> iLen2));
> 			luaC_checkGC(L);
> 		}
> /* agregado por mi => fin */
>         else
>           Arith(L, ra, rb, rc, TM_ADD);
>         break;
>       }

Let me first say that I am pretty new to Lua. There are many who are 
much more experienced than me, and better suited to answer your 
question. But I have special needs of the engine like you, so I have 
been in this section of the code. It seems like you could have used 
luaV_concat() to do this rather than recoding it in-place.

--
chris marrin                ,""$,
cmarrin@arch.sel.sony.com b`    $                             ,,.
(408) 955-3049          mP     b'                            , 1$'
Sony    ,.`           ,b`    ,`                              :$$'
     ,|`             mP    ,`                                       ,mm
   ,b"              b"   ,`            ,mm      m$$    ,m         ,`P$$
  m$`             ,b`  .` ,mm        ,'|$P   ,|"1$`  ,b$P       ,`  :$1
 b$`             ,$: :,`` |$$      ,`   $$` ,|` ,$$,,`"$$     .`    :$|
b$|            _m$`,:`    :$1   ,`     ,$Pm|`    `    :$$,..;"'     |$:
P$b,      _;b$$b$1"       |$$ ,`      ,$$"             ``'          $$
 ```"```'"    `"`         `""`        ""`                          ,P`
"As a general rule,don't solve puzzles that open portals to Hell"'