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

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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