Function zdiffAlgorithm1

app/redis-6.2.6/src/t_zset.c:2394–2446

}

static void zdiffAlgorithm1(zsetopsrc *src, long setnum, zset *dstzset, size_t *maxelelen, size_t *totelelen) {
    /* DIFF Algorithm 1:
     *
     * We perform the diff by iterating all the elements of the first set,
     * and only adding it to the target set if the element does not exist
     * into all the other sets.
     *
     * This way we perform at max N*M operations, where N is the size of
     * the first set, and M the number of sets.
     *
     * There is also a O(K*log(K)) cost for adding the resulting elements
     * to the target set, where K is the final size of the target set.
     *
     * The final complexity of this algorithm is O(N*M + K*log(K)). */
    int j;
    zsetopval zval;
    zskiplistNode *znode;
    sds tmp;

    /* With algorithm 1 it is better to order the sets to subtract
     * by decreasing size, so that we are more likely to find
     * duplicated elements ASAP. */
    qsort(src+1,setnum-1,sizeof(zsetopsrc),zuiCompareByRevCardinality);

    memset(&zval, 0, sizeof(zval));
    zuiInitIterator(&src[0]);
    while (zuiNext(&src[0],&zval)) {
        double value;
        int exists = 0;

        for (j = 1; j < setnum; j++) {
            /* It is not safe to access the zset we are
             * iterating, so explicitly check for equal object.
             * This check isn't really needed anymore since we already
             * check for a duplicate set in the zsetChooseDiffAlgorithm
             * function, but we're leaving it for future-proofing. */
            if (src[j].subject == src[0].subject ||
                zuiFind(&src[j],&zval,&value)) {
                exists = 1;
                break;
            }
        }

        if (!exists) {
            tmp = zuiNewSdsFromValue(&zval);
            znode = zslInsert(dstzset->zsl,zval.score,tmp);
            dictAdd(dstzset->dict,tmp,&znode->score);
            if (sdslen(tmp) > *maxelelen) *maxelelen = sdslen(tmp);
            (*totelelen) += sdslen(tmp);
        }
    }
    zuiClearIterator(&src[0]);
}


static void zdiffAlgorithm2(zsetopsrc *src, long setnum, zset *dstzset, size_t *maxelelen, size_t *totelelen) {