ptcb除了if (ptcb == (OS_TCB *)0) {} 和if (ptcb == (OS_TCB *)1) {}外 ，还有其他情况没？

请问各位大神，ptcb除了if (ptcb == (OS_TCB *)0) {} 和if (ptcb == (OS_TCB *)1) {}外 ，还有其他情况没？在我那个ucosii版本中OSTaskChangePrio（）函数还有其他的函数都有这两种判断，if (ptcb == (OS_TCB *)0) { /* Does task to change exist? */
OS_EXIT_CRI tiCAL(); /* No, can't change its priority! */
return (OS_ERR_PRIO);
}
if (ptcb == OS_TCB_RESERVED) { /* Is task assigned to Mutex */
OS_EXIT_CRITICAL(); /* No, can't change its priority! */
return (OS_ERR_TASK_NOT_EXIST);
}但都是返回函数的。
所以我想问一下ptcb还有没有其他的情况？