Function luaV_concat

third-party/lua-5.2.4/src/lvm.c:293–332

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) || ttisnumber(top-2)) || !tostring(L, top-1)) {
      if (!call_binTM(L, top-2, top-1, top-2, TM_CONCAT))
        luaG_concaterror(L, top-2, top-1);
    }
    else if (tsvalue(top-1)->len == 0)  /* second operand is empty? */
      (void)tostring(L, top - 2);  /* result is first operand */
    else if (ttisstring(top-2) && tsvalue(top-2)->len == 0) {
      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 = tsvalue(top-1)->len;
      char *buffer;
      int i;
      /* collect total length */
      for (i = 1; i < total && tostring(L, top-i-1); i++) {
        size_t l = tsvalue(top-i-1)->len;
        if (l >= (MAX_SIZET/sizeof(char)) - tl)
          luaG_runerror(L, "string length overflow");
        tl += l;
      }
      buffer = luaZ_openspace(L, &G(L)->buff, tl);
      tl = 0;
      n = i;
      do {  /* concat all strings */
        size_t l = tsvalue(top-i)->len;
        memcpy(buffer+tl, svalue(top-i), l * sizeof(char));
        tl += l;
      } while (--i > 0);
      setsvalue2s(L, top-n, luaS_newlstr(L, buffer, tl));
    }
    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 */
}


void luaV_objlen (lua_State *L, StkId ra, const TValue *rb) {