getitem.c

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#include <xinu.h>

pid32 getfirst(qid16 q)
{
    pid32 head;

    if (isempty(q))
    {
        return EMPTY;
    }

    head = queuehead(q);
    return getitem(queuetab[head].qnext);
}

pid32 getlast(qid16 q)
{
    pid32 tail;

    if (isempty(q))
    {
        return EMPTY;
    }

    tail = queuetail(q);
    return getitem(queuetab[tail].qprev);
}

pid32 getitem(
    pid32 pid /* ID of process to remove    */
)
{
    pid32 prev, next;

    next = queuetab[pid].qnext; /* Following node in list   */
    prev = queuetab[pid].qprev; /* Previous node in list    */
    queuetab[prev].qnext = next;
    queuetab[next].qprev = prev;
    return pid;
}