Function zslFirstInRange

src/t_zset.cpp:330–352

Find the first node that is contained in the specified range. * Returns NULL when no element is contained in the range. */

/* Find the first node that is contained in the specified range.
 * Returns NULL when no element is contained in the range. */
zskiplistNode *zslFirstInRange(zskiplist *zsl, zrangespec *range) {
    zskiplistNode *x;
    int i;

    /* If everything is out of range, return early. */
    if (!zslIsInRange(zsl,range)) return NULL;

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        /* Go forward while *OUT* of range. */
        while (x->level(i)->forward &&
            !zslValueGteMin(x->level(i)->forward->score,range))
                x = x->level(i)->forward;
    }

    /* This is an inner range, so the next node cannot be NULL. */
    x = x->level(0)->forward;
    serverAssert(x != NULL);

    /* Check if score <= max. */
    if (!zslValueLteMax(x->score,range)) return NULL;
    return x;
}

/* Find the last node that is contained in the specified range.
 * Returns NULL when no element is contained in the range. */