zset.c

/*
 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*-----------------------------------------------------------------------------
 * Sorted set API
 *----------------------------------------------------------------------------*/

/* ZSETs are ordered sets using two data structures to hold the same elements
 * in order to get O(log(N)) INSERT and REMOVE operations into a sorted
 * data structure.
 *
 * The elements are added to a hash table mapping Redis objects to scores.
 * At the same time the elements are added to a skip list mapping scores
 * to Redis objects (so objects are sorted by scores in this "view").
 *
 * Note that the SDS string representing the element is the same in both
 * the hash table and skiplist in order to save memory. What we do in order
 * to manage the shared SDS string more easily is to free the SDS string
 * only in zslFreeNode(). The dictionary has no value free method set.
 * So we should always remove an element from the dictionary, and later from
 * the skiplist.
 *
 * This skiplist implementation is almost a C translation of the original
 * algorithm described by William Pugh in "Skip Lists: A Probabilistic
 * Alternative to Balanced Trees", modified in three ways:
 * a) this implementation allows for repeated scores.
 * b) the comparison is not just by key (our 'score') but by satellite data.
 * c) there is a back pointer, so it's a doubly linked list with the back
 * pointers being only at "level 1". This allows to traverse the list
 * from tail to head, useful for ZREVRANGE. */

#include <math.h>
#include <assert.h>
#include <stdlib.h>
#include <string.h>

#include "zset.h"
#include "commondef.h"
#include "zmalloc.h"
#include "util.h"
#include "ziplist.h"
#include "intset.h"


/*-----------------------------------------------------------------------------
 * Skiplist implementation of the low level API
 *----------------------------------------------------------------------------*/

/* Create a skiplist node with the specified number of levels.
 * The SDS string 'ele' is referenced by the node after the call. */
zskiplistNode *zslCreateNode(int level, double score, sds ele) {
    zskiplistNode *zn =
        zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
    zn->score = score;
    zn->ele = ele;
    return zn;
}

/* Create a new skiplist. */
zskiplist *zslCreate(void) {
    int j;
    zskiplist *zsl;

    zsl = zmalloc(sizeof(*zsl));
    zsl->level = 1;
    zsl->length = 0;
    zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);
    for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++) {
        zsl->header->level[j].forward = NULL;
        zsl->header->level[j].span = 0;
    }
    zsl->header->backward = NULL;
    zsl->tail = NULL;
    return zsl;
}

/* Free the specified skiplist node. The referenced SDS string representation
 * of the element is freed too, unless node->ele is set to NULL before calling
 * this function. */
void zslFreeNode(zskiplistNode *node) {
    sdsfree(node->ele);
    zfree(node);
}

/* Free a whole skiplist. */
void zslFree(zskiplist *zsl) {
    zskiplistNode *node = zsl->header->level[0].forward, *next;

    zfree(zsl->header);
    while(node) {
        next = node->level[0].forward;
        zslFreeNode(node);
        node = next;
    }
    zfree(zsl);
}

/* Returns a random level for the new skiplist node we are going to create.
 * The return value of this function is between 1 and ZSKIPLIST_MAXLEVEL
 * (both inclusive), with a powerlaw-alike distribution where higher
 * levels are less likely to be returned. */
int zslRandomLevel(void) {
    int level = 1;
    while ((rand()&0xFFFF) < (ZSKIPLIST_P * 0xFFFF))
        level += 1;
    return (level<ZSKIPLIST_MAXLEVEL) ? level : ZSKIPLIST_MAXLEVEL;
}

/* 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'. */
zskiplistNode *zslInsert(zskiplist *zsl, double score, sds ele) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    unsigned int rank[ZSKIPLIST_MAXLEVEL];
    int i, level;

    assert(!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, zslDeleteByScore and zslDeleteByRank */
void zslDeleteNode(zskiplist *zsl, zskiplistNode *x, zskiplistNode **update) {
    int i;
    for (i = 0; i < zsl->level; i++) {
        if (update[i]->level[i].forward == x) {
            update[i]->level[i].span += x->level[i].span - 1;
            update[i]->level[i].forward = x->level[i].forward;
        } else {
            update[i]->level[i].span -= 1;
        }
    }
    if (x->level[0].forward) {
        x->level[0].forward->backward = x->backward;
    } else {
        zsl->tail = x->backward;
    }
    while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
        zsl->level--;
    zsl->length--;
}

/* Delete an element with matching score/element from the skiplist.
 * The function returns 1 if the node was found and deleted, otherwise
 * 0 is returned.
 *
 * If 'node' is NULL the deleted node is freed by zslFreeNode(), otherwise
 * it is not freed (but just unlinked) and *node is set to the node pointer,
 * so that it is possible for the caller to reuse the node (including the
 * referenced SDS string at node->ele). */
int zslDelete(zskiplist *zsl, double score, sds ele, zskiplistNode **node) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    int i;

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        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)))
        {
            x = x->level[i].forward;
        }
        update[i] = x;
    }
    /* We may have multiple elements with the same score, what we need
     * is to find the element with both the right score and object. */
    x = x->level[0].forward;
    if (x && score == x->score && sdscmp(x->ele,ele) == 0) {
        zslDeleteNode(zsl, x, update);
        if (!node)
            zslFreeNode(x);
        else
            *node = x;
        return 1;
    }
    return 0; /* not found */
}

int zslValueGteMin(double value, zrangespec *spec) {
    return spec->minex ? (value > spec->min) : (value >= spec->min);
}

int zslValueLteMax(double value, zrangespec *spec) {
    return spec->maxex ? (value < spec->max) : (value <= spec->max);
}

/* Returns if there is a part of the zset is in range. */
int zslIsInRange(zskiplist *zsl, zrangespec *range) {
    zskiplistNode *x;

    /* Test for ranges that will always be empty. */
    if (range->min > range->max ||
            (range->min == range->max && (range->minex || range->maxex)))
        return 0;
    x = zsl->tail;
    if (x == NULL || !zslValueGteMin(x->score,range))
        return 0;
    x = zsl->header->level[0].forward;
    if (x == NULL || !zslValueLteMax(x->score,range))
        return 0;
    return 1;
}

/* 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;
    assert(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. */
zskiplistNode *zslLastInRange(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 *IN* range. */
        while (x->level[i].forward &&
            zslValueLteMax(x->level[i].forward->score,range))
                x = x->level[i].forward;
    }

    /* This is an inner range, so this node cannot be NULL. */
    assert(x != NULL);

    /* Check if score >= min. */
    if (!zslValueGteMin(x->score,range)) return NULL;
    return x;
}

/* Delete all the elements with score between min and max from the skiplist.
 * Min and max are inclusive, so a score >= min || score <= max is deleted.
 * Note that this function takes the reference to the hash table view of the
 * sorted set, in order to remove the elements from the hash table too. */
unsigned long zslDeleteRangeByScore(zskiplist *zsl, zrangespec *range, dict *dict) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    unsigned long removed = 0;
    int i;

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        while (x->level[i].forward && (range->minex ?
            x->level[i].forward->score <= range->min :
            x->level[i].forward->score < range->min))
                x = x->level[i].forward;
        update[i] = x;
    }

    /* Current node is the last with score < or <= min. */
    x = x->level[0].forward;

    /* Delete nodes while in range. */
    while (x &&
           (range->maxex ? x->score < range->max : x->score <= range->max))
    {
        zskiplistNode *next = x->level[0].forward;
        zslDeleteNode(zsl,x,update);
        dictDelete(dict,x->ele);
        zslFreeNode(x); /* Here is where x->ele is actually released. */
        removed++;
        x = next;
    }
    return removed;
}

unsigned long zslDeleteRangeByLex(zskiplist *zsl, zlexrangespec *range, dict *dict) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    unsigned long removed = 0;
    int i;


    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        while (x->level[i].forward &&
            !zslLexValueGteMin(x->level[i].forward->ele,range))
                x = x->level[i].forward;
        update[i] = x;
    }

    /* Current node is the last with score < or <= min. */
    x = x->level[0].forward;

    /* Delete nodes while in range. */
    while (x && zslLexValueLteMax(x->ele,range)) {
        zskiplistNode *next = x->level[0].forward;
        zslDeleteNode(zsl,x,update);
        dictDelete(dict,x->ele);
        zslFreeNode(x); /* Here is where x->ele is actually released. */
        removed++;
        x = next;
    }
    return removed;
}

/* Delete all the elements with rank between start and end from the skiplist.
 * Start and end are inclusive. Note that start and end need to be 1-based */
unsigned long zslDeleteRangeByRank(zskiplist *zsl, unsigned int start, unsigned int end, dict *dict) {
    zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
    unsigned long traversed = 0, removed = 0;
    int i;

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        while (x->level[i].forward && (traversed + x->level[i].span) < start) {
            traversed += x->level[i].span;
            x = x->level[i].forward;
        }
        update[i] = x;
    }

    traversed++;
    x = x->level[0].forward;
    while (x && traversed <= end) {
        zskiplistNode *next = x->level[0].forward;
        zslDeleteNode(zsl,x,update);
        dictDelete(dict,x->ele);
        zslFreeNode(x);
        removed++;
        traversed++;
        x = next;
    }
    return removed;
}

/* Find the rank for an element by both score and key.
 * Returns 0 when the element cannot be found, rank otherwise.
 * Note that the rank is 1-based due to the span of zsl->header to the
 * first element. */
unsigned long zslGetRank(zskiplist *zsl, double score, sds ele) {
    zskiplistNode *x;
    unsigned long rank = 0;
    int i;

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        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 += x->level[i].span;
            x = x->level[i].forward;
        }

        /* x might be equal to zsl->header, so test if obj is non-NULL */
        if (x->ele && sdscmp(x->ele,ele) == 0) {
            return rank;
        }
    }
    return 0;
}

/* Finds an element by its rank. The rank argument needs to be 1-based. */
zskiplistNode* zslGetElementByRank(zskiplist *zsl, unsigned long rank) {
    zskiplistNode *x;
    unsigned long traversed = 0;
    int i;

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        while (x->level[i].forward && (traversed + x->level[i].span) <= rank)
        {
            traversed += x->level[i].span;
            x = x->level[i].forward;
        }
        if (traversed == rank) {
            return x;
        }
    }
    return NULL;
}

/* Populate the rangespec according to the objects min and max. */
int zslParseRange(robj *min, robj *max, zrangespec *spec) {
    char *eptr;
    spec->minex = spec->maxex = 0;

    /* Parse the min-max interval. If one of the values is prefixed
     * by the "(" character, it's considered "open". For instance
     * ZRANGEBYSCORE zset (1.5 (2.5 will match min < x < max
     * ZRANGEBYSCORE zset 1.5 2.5 will instead match min <= x <= max */
    if (min->encoding == OBJ_ENCODING_INT) {
        spec->min = (long)min->ptr;
    } else {
        if (((char*)min->ptr)[0] == '(') {
            spec->min = strtod((char*)min->ptr+1,&eptr);
            if (eptr[0] != '\0' || isnan(spec->min)) return C_ERR;
            spec->minex = 1;
        } else {
            spec->min = strtod((char*)min->ptr,&eptr);
            if (eptr[0] != '\0' || isnan(spec->min)) return C_ERR;
        }
    }
    if (max->encoding == OBJ_ENCODING_INT) {
        spec->max = (long)max->ptr;
    } else {
        if (((char*)max->ptr)[0] == '(') {
            spec->max = strtod((char*)max->ptr+1,&eptr);
            if (eptr[0] != '\0' || isnan(spec->max)) return C_ERR;
            spec->maxex = 1;
        } else {
            spec->max = strtod((char*)max->ptr,&eptr);
            if (eptr[0] != '\0' || isnan(spec->max)) return C_ERR;
        }
    }

    return C_OK;
}

/* ------------------------ Lexicographic ranges ---------------------------- */

/* Parse max or min argument of ZRANGEBYLEX.
  * (foo means foo (open interval)
  * [foo means foo (closed interval)
  * - means the min string possible
  * + means the max string possible
  *
  * If the string is valid the *dest pointer is set to the redis object
  * that will be used for the comparision, and ex will be set to 0 or 1
  * respectively if the item is exclusive or inclusive. C_OK will be
  * returned.
  *
  * If the string is not a valid range C_ERR is returned, and the value
  * of *dest and *ex is undefined. */
int zslParseLexRangeItem(robj *item, sds *dest, int *ex) {
    char *c = item->ptr;

    switch(c[0]) {
    case '+':
        if (c[1] != '\0') return C_ERR;
        *ex = 1;
        *dest = sdsnew("maxstring");
        return C_OK;
    case '-':
        if (c[1] != '\0') return C_ERR;
        *ex = 1;
        *dest = sdsnew("minstring");
        return C_OK;
    case '(':
        *ex = 1;
        *dest = sdsnewlen(c+1,sdslen(c)-1);
        return C_OK;
    case '[':
        *ex = 0;
        *dest = sdsnewlen(c+1,sdslen(c)-1);
        return C_OK;
    default:
        return C_ERR;
    }
}

/* Free a lex range structure, must be called only after zelParseLexRange()
 * populated the structure with success (C_OK returned). */
void zslFreeLexRange(zlexrangespec *spec) {
    sdsfree(spec->min);
    sdsfree(spec->max);
}

/* Populate the lex rangespec according to the objects min and max.
 *
 * Return C_OK on success. On error C_ERR is returned.
 * When OK is returned the structure must be freed with zslFreeLexRange(),
 * otherwise no release is needed. */
int zslParseLexRange(robj *min, robj *max, zlexrangespec *spec) {
    /* The range can't be valid if objects are integer encoded.
     * Every item must start with ( or [. */
    if (min->encoding == OBJ_ENCODING_INT ||
        max->encoding == OBJ_ENCODING_INT) return C_ERR;

    spec->min = spec->max = NULL;
    if (zslParseLexRangeItem(min, &spec->min, &spec->minex) == C_ERR ||
        zslParseLexRangeItem(max, &spec->max, &spec->maxex) == C_ERR) {
        zslFreeLexRange(spec);
        return C_ERR;
    } else {
        return C_OK;
    }
}

/* This is just a wrapper to sdscmp() that is able to
 * handle shared.minstring and shared.maxstring as the equivalent of
 * -inf and +inf for strings */
int sdscmplex(sds a, sds b) {
    if (a == b) return 0;
    sds minstring = sdsnew("minstring");
    sds maxstring = sdsnew("maxstring");
    if (0 == sdscmp(a, minstring) || 0 == sdscmp(b, maxstring)) {
        sdsfree(minstring);
        sdsfree(maxstring);
        return -1;
    }

    if (0 == sdscmp(a, maxstring) || 0 == sdscmp(b, minstring)) {
        sdsfree(minstring);
        sdsfree(maxstring);
        return 1;
    }

    sdsfree(minstring);
    sdsfree(maxstring);
    return sdscmp(a,b);
}

int zslLexValueGteMin(sds value, zlexrangespec *spec) {
    return spec->minex ?
        (sdscmplex(value,spec->min) > 0) :
        (sdscmplex(value,spec->min) >= 0);
}

int zslLexValueLteMax(sds value, zlexrangespec *spec) {
    return spec->maxex ?
        (sdscmplex(value,spec->max) < 0) :
        (sdscmplex(value,spec->max) <= 0);
}

/* Returns if there is a part of the zset is in the lex range. */
int zslIsInLexRange(zskiplist *zsl, zlexrangespec *range) {
    zskiplistNode *x;

    /* Test for ranges that will always be empty. */
    int cmp = sdscmplex(range->min,range->max);
    if (cmp > 0 || (cmp == 0 && (range->minex || range->maxex)))
        return 0;
    x = zsl->tail;
    if (x == NULL || !zslLexValueGteMin(x->ele,range))
        return 0;
    x = zsl->header->level[0].forward;
    if (x == NULL || !zslLexValueLteMax(x->ele,range))
        return 0;
    return 1;
}

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

    /* If everything is out of range, return early. */
    if (!zslIsInLexRange(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 &&
            !zslLexValueGteMin(x->level[i].forward->ele,range))
                x = x->level[i].forward;
    }

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

    /* Check if score <= max. */
    if (!zslLexValueLteMax(x->ele,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. */
zskiplistNode *zslLastInLexRange(zskiplist *zsl, zlexrangespec *range) {
    zskiplistNode *x;
    int i;

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

    x = zsl->header;
    for (i = zsl->level-1; i >= 0; i--) {
        /* Go forward while *IN* range. */
        while (x->level[i].forward &&
            zslLexValueLteMax(x->level[i].forward->ele,range))
                x = x->level[i].forward;
    }

    /* This is an inner range, so this node cannot be NULL. */
    assert(x != NULL);

    /* Check if score >= min. */
    if (!zslLexValueGteMin(x->ele,range)) return NULL;
    return x;
}

/*-----------------------------------------------------------------------------
 * Ziplist-backed sorted set API
 *----------------------------------------------------------------------------*/
unsigned char *zzlFind(unsigned char *zl, sds ele, double *score) {
    unsigned char *eptr = ziplistIndex(zl,0), *sptr;

    while (eptr != NULL) {
        sptr = ziplistNext(zl,eptr);
        assert(sptr != NULL);

        if (ziplistCompare(eptr,(unsigned char*)ele,sdslen(ele))) {
            /* Matching element, pull out score. */
            if (score != NULL) *score = zzlGetScore(sptr);
            return eptr;
        }

        /* Move to next element. */
        eptr = ziplistNext(zl,sptr);
    }
    return NULL;
}

/* Delete (element,score) pair from ziplist. Use local copy of eptr because we
 * don't want to modify the one given as argument. */
unsigned char *zzlDelete(unsigned char *zl, unsigned char *eptr) {
    unsigned char *p = eptr;

    /* TODO: add function to ziplist API to delete N elements from offset. */
    zl = ziplistDelete(zl,&p);
    zl = ziplistDelete(zl,&p);
    return zl;
}

/* Insert (element,score) pair in ziplist. This function assumes the element is
 * not yet present in the list. */
unsigned char *zzlInsert(unsigned char *zl, sds ele, double score) {
    unsigned char *eptr = ziplistIndex(zl,0), *sptr;
    double s;

    while (eptr != NULL) {
        sptr = ziplistNext(zl,eptr);
        assert(sptr != NULL);
        s = zzlGetScore(sptr);

        if (s > score) {
            /* First element with score larger than score for element to be
             * inserted. This means we should take its spot in the list to
             * maintain ordering. */
            zl = zzlInsertAt(zl,eptr,ele,score);
            break;
        } else if (s == score) {
            /* Ensure lexicographical ordering for elements. */
            if (zzlCompareElements(eptr,(unsigned char*)ele,sdslen(ele)) > 0) {
                zl = zzlInsertAt(zl,eptr,ele,score);
                break;
            }
        }

        /* Move to next element. */
        eptr = ziplistNext(zl,sptr);
    }

    /* Push on tail of list when it was not yet inserted. */
    if (eptr == NULL)
        zl = zzlInsertAt(zl,NULL,ele,score);
    return zl;
}

unsigned int zzlLength(unsigned char *zl) {
    return ziplistLen(zl)/2;
}

double zzlGetScore(unsigned char *sptr) {
    unsigned char *vstr;
    unsigned int vlen;
    long long vlong;
    char buf[128];
    double score;

    assert(sptr != NULL);
    assert(ziplistGet(sptr,&vstr,&vlen,&vlong));

    if (vstr) {
        memcpy(buf,vstr,vlen);
        buf[vlen] = '\0';
        score = strtod(buf,NULL);
    } else {
        score = vlong;
    }

    return score;
}

/* Return a ziplist element as an SDS string. */
sds ziplistGetObject(unsigned char *sptr) {
    unsigned char *vstr;
    unsigned int vlen;
    long long vlong;

    assert(sptr != NULL);
    assert(ziplistGet(sptr,&vstr,&vlen,&vlong));

    if (vstr) {
        return sdsnewlen((char*)vstr,vlen);
    } else {
        return sdsfromlonglong(vlong);
    }
}

/* Compare element in sorted set with given element. */
int zzlCompareElements(unsigned char *eptr, unsigned char *cstr, unsigned int clen) {
    unsigned char *vstr;
    unsigned int vlen;
    long long vlong;
    unsigned char vbuf[32];
    int minlen, cmp;

    assert(ziplistGet(eptr,&vstr,&vlen,&vlong));
    if (vstr == NULL) {
        /* Store string representation of long long in buf. */
        vlen = ll2string((char*)vbuf,sizeof(vbuf),vlong);
        vstr = vbuf;
    }

    minlen = (vlen < clen) ? vlen : clen;
    cmp = memcmp(vstr,cstr,minlen);
    if (cmp == 0) return vlen-clen;
    return cmp;
}

/* Move to next entry based on the values in eptr and sptr. Both are set to
 * NULL when there is no next entry. */
void zzlNext(unsigned char *zl, unsigned char **eptr, unsigned char **sptr) {
    unsigned char *_eptr, *_sptr;
    assert(*eptr != NULL && *sptr != NULL);

    _eptr = ziplistNext(zl,*sptr);
    if (_eptr != NULL) {
        _sptr = ziplistNext(zl,_eptr);
        assert(_sptr != NULL);
    } else {
        /* No next entry. */
        _sptr = NULL;
    }

    *eptr = _eptr;
    *sptr = _sptr;
}

/* Move to the previous entry based on the values in eptr and sptr. Both are
 * set to NULL when there is no next entry. */
void zzlPrev(unsigned char *zl, unsigned char **eptr, unsigned char **sptr) {
    unsigned char *_eptr, *_sptr;
    assert(*eptr != NULL && *sptr != NULL);

    _sptr = ziplistPrev(zl,*eptr);
    if (_sptr != NULL) {
        _eptr = ziplistPrev(zl,_sptr);
        assert(_eptr != NULL);
    } else {
        /* No previous entry. */
        _eptr = NULL;
    }

    *eptr = _eptr;
    *sptr = _sptr;
}

/* Returns if there is a part of the zset is in range. Should only be used
 * internally by zzlFirstInRange and zzlLastInRange. */
int zzlIsInRange(unsigned char *zl, zrangespec *range) {
    unsigned char *p;
    double score;

    /* Test for ranges that will always be empty. */
    if (range->min > range->max ||
            (range->min == range->max && (range->minex || range->maxex)))
        return 0;

    p = ziplistIndex(zl,-1); /* Last score. */
    if (p == NULL) return 0; /* Empty sorted set */
    score = zzlGetScore(p);
    if (!zslValueGteMin(score,range))
        return 0;

    p = ziplistIndex(zl,1); /* First score. */
    assert(p != NULL);
    score = zzlGetScore(p);
    if (!zslValueLteMax(score,range))
        return 0;

    return 1;
}

/* Find pointer to the first element contained in the specified range.
 * Returns NULL when no element is contained in the range. */
unsigned char *zzlFirstInRange(unsigned char *zl, zrangespec *range) {
    unsigned char *eptr = ziplistIndex(zl,0), *sptr;
    double score;

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

    while (eptr != NULL) {
        sptr = ziplistNext(zl,eptr);
        assert(sptr != NULL);

        score = zzlGetScore(sptr);
        if (zslValueGteMin(score,range)) {
            /* Check if score <= max. */
            if (zslValueLteMax(score,range))
                return eptr;
            return NULL;
        }

        /* Move to next element. */
        eptr = ziplistNext(zl,sptr);
    }

    return NULL;
}

/* Find pointer to the last element contained in the specified range.
 * Returns NULL when no element is contained in the range. */
unsigned char *zzlLastInRange(unsigned char *zl, zrangespec *range) {
    unsigned char *eptr = ziplistIndex(zl,-2), *sptr;
    double score;

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

    while (eptr != NULL) {
        sptr = ziplistNext(zl,eptr);
        assert(sptr != NULL);

        score = zzlGetScore(sptr);
        if (zslValueLteMax(score,range)) {
            /* Check if score >= min. */
            if (zslValueGteMin(score,range))
                return eptr;
            return NULL;
        }

        /* Move to previous element by moving to the score of previous element.
         * When this returns NULL, we know there also is no element. */
        sptr = ziplistPrev(zl,eptr);
        if (sptr != NULL)
            assert((eptr = ziplistPrev(zl,sptr)) != NULL);
        else
            eptr = NULL;
    }

    return NULL;
}

int zzlLexValueGteMin(unsigned char *p, zlexrangespec *spec) {
    sds value = ziplistGetObject(p);
    int res = zslLexValueGteMin(value,spec);
    sdsfree(value);
    return res;
}

int zzlLexValueLteMax(unsigned char *p, zlexrangespec *spec) {
    sds value = ziplistGetObject(p);
    int res = zslLexValueLteMax(value,spec);
    sdsfree(value);
    return res;
}

/* Returns if there is a part of the zset is in range. Should only be used
 * internally by zzlFirstInRange and zzlLastInRange. */
int zzlIsInLexRange(unsigned char *zl, zlexrangespec *range) {
    unsigned char *p;

    /* Test for ranges that will always be empty. */
    int cmp = sdscmplex(range->min,range->max);
    if (cmp > 0 || (cmp == 0 && (range->minex || range->maxex)))
        return 0;

    p = ziplistIndex(zl,-2); /* Last element. */
    if (p == NULL) return 0;
    if (!zzlLexValueGteMin(p,range))
        return 0;

    p = ziplistIndex(zl,0); /* First element. */
    assert(p != NULL);
    if (!zzlLexValueLteMax(p,range))
        return 0;

    return 1;
}

/* Find pointer to the first element contained in the specified lex range.
 * Returns NULL when no element is contained in the range. */
unsigned char *zzlFirstInLexRange(unsigned char *zl, zlexrangespec *range) {
    unsigned char *eptr = ziplistIndex(zl,0), *sptr;

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

    while (eptr != NULL) {
        if (zzlLexValueGteMin(eptr,range)) {
            /* Check if score <= max. */
            if (zzlLexValueLteMax(eptr,range))
                return eptr;
            return NULL;
        }

        /* Move to next element. */
        sptr = ziplistNext(zl,eptr); /* This element score. Skip it. */
        assert(sptr != NULL);
        eptr = ziplistNext(zl,sptr); /* Next element. */
    }

    return NULL;
}

/* Find pointer to the last element contained in the specified lex range.
 * Returns NULL when no element is contained in the range. */
unsigned char *zzlLastInLexRange(unsigned char *zl, zlexrangespec *range) {
    unsigned char *eptr = ziplistIndex(zl,-2), *sptr;

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

    while (eptr != NULL) {
        if (zzlLexValueLteMax(eptr,range)) {
            /* Check if score >= min. */
            if (zzlLexValueGteMin(eptr,range))
                return eptr;
            return NULL;
        }

        /* Move to previous element by moving to the score of previous element.
         * When this returns NULL, we know there also is no element. */
        sptr = ziplistPrev(zl,eptr);
        if (sptr != NULL)
            assert((eptr = ziplistPrev(zl,sptr)) != NULL);
        else
            eptr = NULL;
    }

    return NULL;
}

unsigned char *zzlInsertAt(unsigned char *zl, unsigned char *eptr, sds ele, double score) {
    unsigned char *sptr;
    char scorebuf[128];
    int scorelen;
    size_t offset;

    scorelen = d2string(scorebuf,sizeof(scorebuf),score);
    if (eptr == NULL) {
        zl = ziplistPush(zl,(unsigned char*)ele,sdslen(ele),ZIPLIST_TAIL);
        zl = ziplistPush(zl,(unsigned char*)scorebuf,scorelen,ZIPLIST_TAIL);
    } else {
        /* Keep offset relative to zl, as it might be re-allocated. */
        offset = eptr-zl;
        zl = ziplistInsert(zl,eptr,(unsigned char*)ele,sdslen(ele));
        eptr = zl+offset;

        /* Insert score after the element. */
        assert((sptr = ziplistNext(zl,eptr)) != NULL);
        zl = ziplistInsert(zl,sptr,(unsigned char*)scorebuf,scorelen);
    }
    return zl;
}

unsigned char *zzlDeleteRangeByScore(unsigned char *zl, zrangespec *range, unsigned long *deleted) {
    unsigned char *eptr, *sptr;
    double score;
    unsigned long num = 0;

    if (deleted != NULL) *deleted = 0;

    eptr = zzlFirstInRange(zl,range);
    if (eptr == NULL) return zl;

    /* When the tail of the ziplist is deleted, eptr will point to the sentinel
     * byte and ziplistNext will return NULL. */
    while ((sptr = ziplistNext(zl,eptr)) != NULL) {
        score = zzlGetScore(sptr);
        if (zslValueLteMax(score,range)) {
            /* Delete both the element and the score. */
            zl = ziplistDelete(zl,&eptr);
            zl = ziplistDelete(zl,&eptr);
            num++;
        } else {
            /* No longer in range. */
            break;
        }
    }

    if (deleted != NULL) *deleted = num;
    return zl;
}

unsigned char *zzlDeleteRangeByLex(unsigned char *zl, zlexrangespec *range, unsigned long *deleted) {
    unsigned char *eptr, *sptr;
    unsigned long num = 0;

    if (deleted != NULL) *deleted = 0;

    eptr = zzlFirstInLexRange(zl,range);
    if (eptr == NULL) return zl;

    /* When the tail of the ziplist is deleted, eptr will point to the sentinel
     * byte and ziplistNext will return NULL. */
    while ((sptr = ziplistNext(zl,eptr)) != NULL) {
        if (zzlLexValueLteMax(eptr,range)) {
            /* Delete both the element and the score. */
            zl = ziplistDelete(zl,&eptr);
            zl = ziplistDelete(zl,&eptr);
            num++;
        } else {
            /* No longer in range. */
            break;
        }
    }

    if (deleted != NULL) *deleted = num;
    return zl;
}

/* Delete all the elements with rank between start and end from the skiplist.
 * Start and end are inclusive. Note that start and end need to be 1-based */
unsigned char *zzlDeleteRangeByRank(unsigned char *zl, unsigned int start, unsigned int end, unsigned long *deleted) {
    unsigned int num = (end-start)+1;
    if (deleted) *deleted = num;
    zl = ziplistDeleteRange(zl,2*(start-1),2*num);
    return zl;
}

/*-----------------------------------------------------------------------------
 * Common sorted set API
 *----------------------------------------------------------------------------*/
unsigned int zsetLength(const robj *zobj) {
    int length = -1;
    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
        length = zzlLength(zobj->ptr);
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
        length = ((const zset*)zobj->ptr)->zsl->length;
    } else {
        // serverPanic("Unknown sorted set encoding");
    }
    return length;
}

void zsetConvert(robj *zobj, int encoding) {
    zset *zs;
    zskiplistNode *node, *next;
    sds ele;
    double score;

    if (zobj->encoding == encoding) return;
    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *zl = zobj->ptr;
        unsigned char *eptr, *sptr;
        unsigned char *vstr;
        unsigned int vlen;
        long long vlong;

        if (encoding != OBJ_ENCODING_SKIPLIST) return;
            // serverPanic("Unknown target encoding");

        zs = zmalloc(sizeof(*zs));
        zs->dict = dictCreate(&zsetDictType,NULL);
        zs->zsl = zslCreate();

        eptr = ziplistIndex(zl,0);
        assert(eptr != NULL);
        sptr = ziplistNext(zl,eptr);
        assert(sptr != NULL);

        while (eptr != NULL) {
            score = zzlGetScore(sptr);
            assert(ziplistGet(eptr,&vstr,&vlen,&vlong));
            if (vstr == NULL)
                ele = sdsfromlonglong(vlong);
            else
                ele = sdsnewlen((char*)vstr,vlen);

            node = zslInsert(zs->zsl,score,ele);
            assert(dictAdd(zs->dict,ele,&node->score) == DICT_OK);
            zzlNext(zl,&eptr,&sptr);
        }

        zfree(zobj->ptr);
        zobj->ptr = zs;
        zobj->encoding = OBJ_ENCODING_SKIPLIST;
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
        unsigned char *zl = ziplistNew();

        if (encoding != OBJ_ENCODING_ZIPLIST) return;
            // serverPanic("Unknown target encoding");

        /* Approach similar to zslFree(), since we want to free the skiplist at
         * the same time as creating the ziplist. */
        zs = zobj->ptr;
        dictRelease(zs->dict);
        node = zs->zsl->header->level[0].forward;
        zfree(zs->zsl->header);
        zfree(zs->zsl);

        while (node) {
            zl = zzlInsertAt(zl,NULL,node->ele,node->score);
            next = node->level[0].forward;
            zslFreeNode(node);
            node = next;
        }

        zfree(zs);
        zobj->ptr = zl;
        zobj->encoding = OBJ_ENCODING_ZIPLIST;
    } else {
        // serverPanic("Unknown sorted set encoding");
    }
}

/* Convert the sorted set object into a ziplist if it is not already a ziplist
 * and if the number of elements and the maximum element size is within the
 * expected ranges. */
void zsetConvertToZiplistIfNeeded(robj *zobj, size_t maxelelen) {
    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) return;
    zset *zset = zobj->ptr;

    if (zset->zsl->length <= OBJ_ZSET_MAX_ZIPLIST_ENTRIES &&
        maxelelen <= OBJ_ZSET_MAX_ZIPLIST_VALUE)
            zsetConvert(zobj,OBJ_ENCODING_ZIPLIST);
}

/* Return (by reference) the score of the specified member of the sorted set
 * storing it into *score. If the element does not exist C_ERR is returned
 * otherwise C_OK is returned and *score is correctly populated.
 * If 'zobj' or 'member' is NULL, C_ERR is returned. */
int zsetScore(robj *zobj, sds member, double *score) {
    if (!zobj || !member) return C_ERR;

    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
        if (zzlFind(zobj->ptr, member, score) == NULL) return C_ERR;
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
        zset *zs = zobj->ptr;
        dictEntry *de = dictFind(zs->dict, member);
        if (de == NULL) return C_ERR;
        *score = *(double*)dictGetVal(de);
    } else {
        // serverPanic("Unknown sorted set encoding");
    }
    return C_OK;
}

/* Add a new element or update the score of an existing element in a sorted
 * set, regardless of its encoding.
 *
 * The set of flags change the command behavior. They are passed with an integer
 * pointer since the function will clear the flags and populate them with
 * other flags to indicate different conditions.
 *
 * The input flags are the following:
 *
 * ZADD_INCR: Increment the current element score by 'score' instead of updating
 *            the current element score. If the element does not exist, we
 *            assume 0 as previous score.
 * ZADD_NX:   Perform the operation only if the element does not exist.
 * ZADD_XX:   Perform the operation only if the element already exist.
 *
 * When ZADD_INCR is used, the new score of the element is stored in
 * '*newscore' if 'newscore' is not NULL.
 *
 * The returned flags are the following:
 *
 * ZADD_NAN:     The resulting score is not a number.
 * ZADD_ADDED:   The element was added (not present before the call).
 * ZADD_UPDATED: The element score was updated.
 * ZADD_NOP:     No operation was performed because of NX or XX.
 *
 * Return value:
 *
 * The function returns 1 on success, and sets the appropriate flags
 * ADDED or UPDATED to signal what happened during the operation (note that
 * none could be set if we re-added an element using the same score it used
 * to have, or in the case a zero increment is used).
 *
 * The function returns 0 on erorr, currently only when the increment
 * produces a NAN condition, or when the 'score' value is NAN since the
 * start.
 *
 * The commad as a side effect of adding a new element may convert the sorted
 * set internal encoding from ziplist to hashtable+skiplist.
 *
 * Memory managemnet of 'ele':
 *
 * The function does not take ownership of the 'ele' SDS string, but copies
 * it if needed. */
int zsetAdd(robj *zobj, double score, sds ele, int *flags, double *newscore) {
    /* Turn options into simple to check vars. */
    int incr = (*flags & ZADD_INCR) != 0;
    int nx = (*flags & ZADD_NX) != 0;
    int xx = (*flags & ZADD_XX) != 0;
    *flags = 0; /* We'll return our response flags. */
    double curscore;

    /* NaN as input is an error regardless of all the other parameters. */
    if (isnan(score)) {
        *flags = ZADD_NAN;
        return 0;
    }

    /* Update the sorted set according to its encoding. */
    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *eptr;

        if ((eptr = zzlFind(zobj->ptr,ele,&curscore)) != NULL) {
            /* NX? Return, same element already exists. */
            if (nx) {
                *flags |= ZADD_NOP;
                return 1;
            }

            /* Prepare the score for the increment if needed. */
            if (incr) {
                score += curscore;
                if (isnan(score)) {
                    *flags |= ZADD_NAN;
                    return 0;
                }
                if (newscore) *newscore = score;
            }

            /* Remove and re-insert when score changed. */
            if (score != curscore) {
                zobj->ptr = zzlDelete(zobj->ptr,eptr);
                zobj->ptr = zzlInsert(zobj->ptr,ele,score);
                *flags |= ZADD_UPDATED;
            }
            return 1;
        } else if (!xx) {
            /* Optimize: check if the element is too large or the list
             * becomes too long *before* executing zzlInsert. */
            zobj->ptr = zzlInsert(zobj->ptr,ele,score);
            if (zzlLength(zobj->ptr) > OBJ_ZSET_MAX_ZIPLIST_ENTRIES)
                zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);
            if (sdslen(ele) > OBJ_ZSET_MAX_ZIPLIST_VALUE)
                zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);
            if (newscore) *newscore = score;
            *flags |= ZADD_ADDED;
            return 1;
        } else {
            *flags |= ZADD_NOP;
            return 1;
        }
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
        zset *zs = zobj->ptr;
        zskiplistNode *znode;
        dictEntry *de;

        de = dictFind(zs->dict,ele);
        if (de != NULL) {
            /* NX? Return, same element already exists. */
            if (nx) {
                *flags |= ZADD_NOP;
                return 1;
            }
            curscore = *(double*)dictGetVal(de);

            /* Prepare the score for the increment if needed. */
            if (incr) {
                score += curscore;
                if (isnan(score)) {
                    *flags |= ZADD_NAN;
                    return 0;
                }
                if (newscore) *newscore = score;
            }

            /* Remove and re-insert when score changes. */
            if (score != curscore) {
                zskiplistNode *node;
                assert(zslDelete(zs->zsl,curscore,ele,&node));
                znode = zslInsert(zs->zsl,score,node->ele);
                /* We reused the node->ele SDS string, free the node now
                 * since zslInsert created a new one. */
                node->ele = NULL;
                zslFreeNode(node);
                /* Note that we did not removed the original element from
                 * the hash table representing the sorted set, so we just
                 * update the score. */
                dictGetVal(de) = &znode->score; /* Update score ptr. */
                *flags |= ZADD_UPDATED;
            }
            return 1;
        } else if (!xx) {
            ele = sdsdup(ele);
            znode = zslInsert(zs->zsl,score,ele);
            assert(dictAdd(zs->dict,ele,&znode->score) == DICT_OK);
            *flags |= ZADD_ADDED;
            if (newscore) *newscore = score;
            return 1;
        } else {
            *flags |= ZADD_NOP;
            return 1;
        }
    } else {
        // serverPanic("Unknown sorted set encoding");
    }
    return 0; /* Never reached. */
}

/* Delete the element 'ele' from the sorted set, returning 1 if the element
 * existed and was deleted, 0 otherwise (the element was not there). */
int zsetDel(robj *zobj, sds ele) {
    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *eptr;

        if ((eptr = zzlFind(zobj->ptr,ele,NULL)) != NULL) {
            zobj->ptr = zzlDelete(zobj->ptr,eptr);
            return 1;
        }
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
        zset *zs = zobj->ptr;
        dictEntry *de;
        double score;

        de = dictUnlink(zs->dict,ele);
        if (de != NULL) {
            /* Get the score in order to delete from the skiplist later. */
            score = *(double*)dictGetVal(de);

            /*Delete from the hash table and later from the skiplist.
             * Note that the order is important: deleting from the skiplist
             * actually releases the SDS string representing the element,
             * which is shared between the skiplist and the hash table, so
             * we need to delete from the skiplist as the final step.*/
            dictFreeUnlinkedEntry(zs->dict,de);

            /* Delete from skiplist. */
            int retval = zslDelete(zs->zsl,score,ele,NULL);
            assert(retval);

            if (htNeedsResize(zs->dict)) dictResize(zs->dict);
            return 1;
        }
    } else {
        // serverPanic("Unknown sorted set encoding");
    }
    return 0; /* No such element found. */
}

/* Given a sorted set object returns the 0-based rank of the object or
 * -1 if the object does not exist.
 *
 * For rank we mean the position of the element in the sorted collection
 * of elements. So the first element has rank 0, the second rank 1, and so
 * forth up to length-1 elements.
 *
 * If 'reverse' is false, the rank is returned considering as first element
 * the one with the lowest score. Otherwise if 'reverse' is non-zero
 * the rank is computed considering as element with rank 0 the one with
 * the highest score. */
long zsetRank(robj *zobj, sds ele, int reverse) {
    unsigned long llen;
    unsigned long rank;

    llen = zsetLength(zobj);

    if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *zl = zobj->ptr;
        unsigned char *eptr, *sptr;

        eptr = ziplistIndex(zl,0);
        assert(eptr != NULL);
        sptr = ziplistNext(zl,eptr);
        assert(sptr != NULL);

        rank = 1;
        while(eptr != NULL) {
            if (ziplistCompare(eptr,(unsigned char*)ele,sdslen(ele)))
                break;
            rank++;
            zzlNext(zl,&eptr,&sptr);
        }

        if (eptr != NULL) {
            if (reverse)
                return llen-rank;
            else
                return rank-1;
        } else {
            return -1;
        }
    } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
        zset *zs = zobj->ptr;
        zskiplist *zsl = zs->zsl;
        dictEntry *de;
        double score;

        de = dictFind(zs->dict,ele);
        if (de != NULL) {
            score = *(double*)dictGetVal(de);
            rank = zslGetRank(zsl,score,ele);
            /* Existing elements always have a rank. */
            assert(rank != 0);
            if (reverse)
                return llen-rank;
            else
                return rank-1;
        } else {
            return -1;
        }
    } else {
        return -1;
        // serverPanic("Unknown sorted set encoding");
    }
}