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Annotation of 43BSD/contrib/icon/functions/pop.c, revision 1.1

1.1     ! root        1: #include "../h/rt.h"
        !             2: 
        !             3: /*
        !             4:  * pop(x) - pop an element from beginning of list x.
        !             5:  */
        !             6: 
        !             7: Xpop(nargs, arg1, arg0)
        !             8: int nargs;
        !             9: struct descrip arg1, arg0;
        !            10:    {
        !            11:    register int i;
        !            12:    register struct b_list *hp;
        !            13:    register struct b_lelem *bp;
        !            14:    extern struct b_lelem *alclstb();
        !            15: 
        !            16:    /*
        !            17:     * x must be a list.
        !            18:     */
        !            19:    DeRef(arg1)
        !            20:    if (QUAL(arg1) || TYPE(arg1) != T_LIST)
        !            21:       runerr(108, &arg1);
        !            22: 
        !            23:    /*
        !            24:     * Fail if the list is empty.
        !            25:     */
        !            26:    hp = (struct b_list *) BLKLOC(arg1);
        !            27:    if (hp->cursize <= 0)
        !            28:       fail();
        !            29: 
        !            30:    /*
        !            31:     * Point bp at the first list block.  If the first block has no
        !            32:     *  elements in use, point bp at the next list block.
        !            33:     */
        !            34:    bp = (struct b_lelem *) BLKLOC(hp->listhead);
        !            35:    if (bp->nused <= 0) {
        !            36:       bp = (struct b_lelem *) BLKLOC(bp->listnext);
        !            37:       BLKLOC(hp->listhead) = (union block *) bp;
        !            38:       bp->listprev = nulldesc;
        !            39:       }
        !            40:    /*
        !            41:     * Locate first element and assign it to arg0 for return.
        !            42:     */
        !            43:    i = bp->first;
        !            44:    arg0 = bp->lslots[i];
        !            45:    /*
        !            46:     * Set bp->first to new first element, or 0 if the block is now
        !            47:     *  empty.  Decrement the usage count for the block and the size
        !            48:     *  of the list.
        !            49:     */
        !            50:    if (++i >= bp->nelem)
        !            51:       i = 0;
        !            52:    bp->first = i;
        !            53:    bp->nused--;
        !            54:    hp->cursize--;
        !            55:    }
        !            56: 
        !            57: Procblock(pop,1)

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