static void fixforjump (FuncState *fs, int pc, int dest, int back) {
  Instruction *jmp = &fs->f->code[pc];
  int offset = dest - (pc + 1);
  if (back)
    offset = -offset;
  if (l_unlikely(offset > MAXARG_Bx))
    luaX_syntaxerror(fs->ls, "control structure too long");
  SETARG_Bx(*jmp, offset);
}