Function RM_ZsetRangePrev

src/module.cpp:3073–3132

Go to the previous element of the sorted set iterator. Returns 1 if there was * a previous element, 0 if we are already at the first element or the range * does not include any item at all. */

 * a previous element, 0 if we are already at the first element or the range
 * does not include any item at all. */
int RM_ZsetRangePrev(RedisModuleKey *key) {
    if (!key->value || key->value->type != OBJ_ZSET) return 0;
    if (!key->u.zset.type || !key->u.zset.current) return 0; /* No active iterator. */

    if (key->value->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *zl = (unsigned char*)ptrFromObj(key->value);
        unsigned char *eptr = (unsigned char*)key->u.zset.current;
        unsigned char *prev;
        prev = ziplistPrev(zl,eptr); /* Go back to previous score. */
        if (prev) prev = ziplistPrev(zl,prev); /* Back to previous ele. */
        if (prev == NULL) {
            key->u.zset.er = 1;
            return 0;
        } else {
            /* Are we still within the range? */
            if (key->u.zset.type == REDISMODULE_ZSET_RANGE_SCORE) {
                /* Fetch the previous element score for the
                 * range check. */
                unsigned char *saved_prev = prev;
                prev = ziplistNext(zl,prev); /* Skip element to get the score.*/
                double score = zzlGetScore(prev); /* Obtain the prev score. */
                if (!zslValueGteMin(score,&key->u.zset.rs)) {
                    key->u.zset.er = 1;
                    return 0;
                }
                prev = saved_prev;
            } else if (key->u.zset.type == REDISMODULE_ZSET_RANGE_LEX) {
                if (!zzlLexValueGteMin(prev,&key->u.zset.lrs)) {
                    key->u.zset.er = 1;
                    return 0;
                }
            }
            key->u.zset.current = prev;
            return 1;
        }
    } else if (key->value->encoding == OBJ_ENCODING_SKIPLIST) {
        zskiplistNode *ln = (zskiplistNode*)key->u.zset.current, *prev = ln->backward;
        if (prev == NULL) {
            key->u.zset.er = 1;
            return 0;
        } else {
            /* Are we still within the range? */
            if (key->u.zset.type == REDISMODULE_ZSET_RANGE_SCORE &&
                !zslValueGteMin(prev->score,&key->u.zset.rs))
            {
                key->u.zset.er = 1;
                return 0;
            } else if (key->u.zset.type == REDISMODULE_ZSET_RANGE_LEX) {
                if (!zslLexValueGteMin(prev->ele,&key->u.zset.lrs)) {
                    key->u.zset.er = 1;
                    return 0;
                }
            }
            key->u.zset.current = prev;
            return 1;
        }
    } else {
        serverPanic("Unsupported zset encoding");