Function zslInsert

src/t_zset.cpp:132–187

Insert a new node in the skiplist. Assumes the element does not already * exist (up to the caller to enforce that). The skiplist takes ownership * of the passed SDS string 'ele'. */

 * exist (up to the caller to enforce that). The skiplist takes ownership
 * of the passed SDS string 'ele'. */
zskiplistNode *zslInsert(zskiplist *zsl, double score, sds ele) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    unsigned int rank[ZSKIPLIST_MAXLEVEL];
    int i, level;

    serverAssert(!std::isnan(score));
    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        /* store rank that is crossed to reach the insert position */
        rank[i] = i == (zsl->level-1) ? 0 : rank[i+1];
        while (x->level(i)->forward &&
                (x->level(i)->forward->score < score ||
                    (x->level(i)->forward->score == score &&
                    sdscmp(x->level(i)->forward->ele,ele) < 0)))
        {
            rank[i] += x->level(i)->span;
            x = x->level(i)->forward;
        }
        update[i] = x;
    }
    /* we assume the element is not already inside, since we allow duplicated
     * scores, reinserting the same element should never happen since the
     * caller of zslInsert() should test in the hash table if the element is
     * already inside or not. */
    level = zslRandomLevel();
    if (level > zsl->level) {
        for (i = zsl->level; i < level; i++) {
            rank[i] = 0;
            update[i] = zsl->header;
            update[i]->level(i)->span = zsl->length;
        }
        zsl->level = level;
    }
    x = zslCreateNode(level,score,ele);
    for (i = 0; i < level; i++) {
        x->level(i)->forward = update[i]->level(i)->forward;
        update[i]->level(i)->forward = x;

        /* update span covered by update[i] as x is inserted here */
        x->level(i)->span = update[i]->level(i)->span - (rank[0] - rank[i]);
        update[i]->level(i)->span = (rank[0] - rank[i]) + 1;
    }

    /* increment span for untouched levels */
    for (i = level; i < zsl->level; i++) {
        update[i]->level(i)->span++;
    }

    x->backward = (update[0] == zsl->header) ? NULL : update[0];
    if (x->level(0)->forward)
        x->level(0)->forward->backward = x;
    else
        zsl->tail = x;
    zsl->length++;
    return x;
}

/* Internal function used by zslDelete, zslDeleteRangeByScore and