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Annotation of 43BSD/contrib/icon/functions/pull.c, revision 1.1.1.1

1.1       root        1: #include "../h/rt.h"
                      2: 
                      3: /*
                      4:  * pull(x) - pull an element from end of list x.
                      5:  */
                      6: 
                      7: Xpull(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:     * Point at list header block and fail if the list is empty.
                     25:     */
                     26:    hp = (struct b_list *) BLKLOC(arg1);
                     27:    if (hp->cursize <= 0)
                     28:       fail();
                     29:    /*
                     30:     * Point bp at the last list element block.  If the last block has no
                     31:     *  elements in use, point bp at the previous list element block.
                     32:     */
                     33:    bp = (struct b_lelem *) BLKLOC(hp->listtail);
                     34:    if (bp->nused <= 0) {
                     35:       bp = (struct b_lelem *) BLKLOC(bp->listprev);
                     36:       BLKLOC(hp->listtail) = (union block *) bp;
                     37:       bp->listnext = nulldesc;
                     38:       }
                     39:    /*
                     40:     * Set i to position of last element and assign the element to
                     41:     *  arg0 for return.  Decrement the usage count for the block
                     42:     *  and the size of the list.
                     43:     */
                     44:    i = bp->first + bp->nused - 1;
                     45:    if (i >= bp->nelem)
                     46:       i -= bp->nelem;
                     47:    arg0 = bp->lslots[i];
                     48:    bp->nused--;
                     49:    hp->cursize--;
                     50:    }
                     51: 
                     52: Procblock(pull,1)

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