Semaphore wait() and signal()

I think it's an inaccuracy in your source. Atomic for the wait() operation means each iteration of it is atomic, meaning S-- is performed without interruption, but the whole operation is interruptible after each completion of S-- inside the while loop.

I don't think, keeping an infinite while loop inside the wait() operation is wise. I would go for Stallings' example;

void semWait(semaphore s){
    s.count--;
    if(s.count<0)
        *place this process in s.queue and block this process
}