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

1.1     ! root        1: #include "../h/rt.h"
        !             2: 
        !             3: /*
        !             4:  * push(x,val) - push val onto beginning of list x.
        !             5:  */
        !             6: Xpush(nargs, arg2, arg1, arg0)
        !             7: int nargs;
        !             8: struct descrip arg2, arg1, arg0;
        !             9:    {
        !            10:    register int i;
        !            11:    register struct b_list *hp;
        !            12:    register struct b_lelem *bp;
        !            13:    extern struct b_lelem *alclstb();
        !            14: 
        !            15:    /*
        !            16:     * x must be a list.
        !            17:     */
        !            18:    DeRef(arg1)
        !            19:    DeRef(arg2)
        !            20:    if (QUAL(arg1) || TYPE(arg1) != T_LIST)
        !            21:       runerr(108, &arg1);
        !            22: 
        !            23:    /*
        !            24:     * A new list element block might be needed, so ensure space for it.
        !            25:     */
        !            26:    hneed(sizeof(struct b_lelem)+LISTBLKSIZE*sizeof(struct descrip));
        !            27: 
        !            28:    /*
        !            29:     * Point hp at the list header block and bp at the first
        !            30:     * list element block.
        !            31:     */
        !            32:    hp = (struct b_list *) BLKLOC(arg1);
        !            33:    bp = (struct b_lelem *) BLKLOC(hp->listhead);
        !            34:    /*
        !            35:     * If the first list element block is full,
        !            36:     * allocate a new list element block, make it the first list
        !            37:     *  element block and make it the previous block of the
        !            38:     *  former first list element block.
        !            39:     */
        !            40:    if (bp->nused >= bp->nelem) {
        !            41:       bp = alclstb(LISTBLKSIZE, 0, 0);
        !            42:       BLKLOC(hp->listhead)->lelem.listprev.type = D_LELEM;
        !            43:       BLKLOC(BLKLOC(hp->listhead)->lelem.listprev) = (union block *) bp;
        !            44:       bp->listnext = hp->listhead;
        !            45:       BLKLOC(hp->listhead) = (union block *) bp;
        !            46:       }
        !            47:    /*
        !            48:     * Set i to position of new first element and assign val (arg2) to
        !            49:     *  that element.
        !            50:     */
        !            51:    i = bp->first - 1;
        !            52:    if (i < 0)
        !            53:       i = bp->nelem - 1;
        !            54:    bp->lslots[i] = arg2;
        !            55:    /*
        !            56:     * Adjust value of location of first element, block usage count,
        !            57:     *  and current list size.
        !            58:     */
        !            59:    bp->first = i;
        !            60:    bp->nused++;
        !            61:    hp->cursize++;
        !            62:    /*
        !            63:     * Return the list.
        !            64:     */
        !            65:    arg0 = arg1;
        !            66:    }
        !            67: 
        !            68: Procblock(push,2)

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