Function luaV_concat

src/Chain/libraries/glua/lvm.cpp:520–557

** Main operation for concatenation: concat 'total' values in the stack, ** from 'L->top - total' up to 'L->top - 1'. */

** from 'L->top - total' up to 'L->top - 1'.
*/
void luaV_concat(lua_State *L, int total) {
    lua_assert(total >= 2);
    do {
        StkId top = L->top;
        int n = 2;  /* number of elements handled in this pass (at least 2) */
        if (!(ttisstring(top - 2) || cvt2str(top - 2)) || !tostring(L, top - 1))
            luaT_trybinTM(L, top - 2, top - 1, top - 2, TM_CONCAT);
        else if (isemptystr(top - 1))  /* second operand is empty? */
            cast_void(tostring(L, top - 2));  /* result is first operand */
        else if (isemptystr(top - 2)) {  /* first operand is an empty string? */
            setobjs2s(L, top - 2, top - 1);  /* result is second op. */
        }
        else {
            /* at least two non-empty string values; get as many as possible */
            size_t tl = vslen(top - 1);
            TString *ts;
            /* collect total length and number of strings */
            for (n = 1; n < total && tostring(L, top - n - 1); n++) {
                size_t l = vslen(top - n - 1);
                if (l >= (MAX_SIZE / sizeof(char)) - tl)
                    luaG_runerror(L, "string length overflow");
                tl += l;
            }
            if (tl <= LUAI_MAXSHORTLEN) {  /* is result a short string? */
                char buff[LUAI_MAXSHORTLEN];
                copy2buff(top, n, buff);  /* copy strings to buffer */
                ts = luaS_newlstr(L, buff, tl);
            }
            else {  /* long string; copy strings directly to final result */
                ts = luaS_createlngstrobj(L, tl);
                copy2buff(top, n, getstr(ts));
            }
            setsvalue2s(L, top - n, ts);  /* create result */
        }
        total -= n - 1;  /* got 'n' strings to create 1 new */
        L->top -= n - 1;  /* popped 'n' strings and pushed one */
    } while (total > 1);  /* repeat until only 1 result left */
}


/*