text: /*
   * 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 "server.h"
  #include <math.h>
  
  /*-----------------------------------------------------------------------------
   * Skiplist implementation of the low level API
   *----------------------------------------------------------------------------*/
  
  int zslLexValueGteMin(sds value, zlexrangespec *spec);
  int zslLexValueLteMax(sds value, zlexrangespec *spec);
  
  /* Create a skiplist node with the specified number of levels.
   * The SDS string 'ele' is referenced by the node after the call. */
  /**
   * 新建一个指定层高的跳跃表节点（指定层高，分值，元素）
   * @param level
   * @param score
   * @param ele
   * @return
   */
  zskiplistNode *zslCreateNode(int level, double score, sds ele) {
      /**
       * 这里不太容易理解
       * 1、首先
       * zskiplistNode *zn =
       *   zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
       *   这句代码中
       *   sizeof(*zn)中的*zn是哪里的？？其实相当于是：
       *   zskiplistNode *zn ；
       *   *zn=zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
       *   zn表示的就是zskiplistNode这个结构体。
       *
       *   2、其次内存分配大小为什么是zskiplistNode结构体
       *   大小+这个结构体的内部结构zskiplistLevel*level？？
       *   答：zskiplistLevel是zskiplistNode结构体中的柔性数组，所以g++编译的时候，他的内存大小
       *   是0，这个也比较容易理解：因为是柔性数组，数组大小不确定，所以开辟内存大小为0.
       *   所以必须单独计算：层数（也就是level，即数组个数）*zskiplistLevel（单个数组）
       *   那么再加上zskiplistNode结构体大小（g++编译时数组部分是0，所以实际大小是除数组以外的空间），
       *   正好是整个节点的内存空间大小
       *
       */
      zskiplistNode *zn =
          zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
      zn->score = score;//赋分值
      zn->ele = ele;//赋元素(sds结构)
      return zn;
  }
  
  /* Create a new skiplist. */
  /**
   * 初始化一个skiplist
   * @return
   */
  zskiplist *zslCreate(void) {
      int j;
      zskiplist *zsl;
      //先开辟内存空间
      zsl = zmalloc(sizeof(*zsl));
      zsl->level = 1;//初始值为1，（最底层，也就是level0），层数level就是1
      zsl->length = 0;//节点数为0（初始化时还没有节点）
      //头指针指向的是头节点（这里要结合示意图理解），头结点不是真正的有效节点，头节点有32层结构，分值是0，元素是null
      zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);
      //每层初始化(看示意图)，前向指针指向null（因为有效节点还没有创建），跨度也是0
      for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++) {
          zsl->header->level[j].forward = NULL;
          zsl->header->level[j].span = 0;
      }
      zsl->header->backward = NULL;//头结点的后向指针为null
      zsl->tail = NULL;//尾指针是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. */
  /**
   * 释放单个节点
   * @param node
   */
  void zslFreeNode(zskiplistNode *node) {
      sdsfree(node->ele);
      zfree(node);
  }
  
  /* Free a whole skiplist. */
  /**
   * 删除整张跳表
   * @param zsl
   */
  void zslFree(zskiplist *zsl) {
      zskiplistNode *node = zsl->header->level[0].forward, *next;
      //删除逻辑：从头节点的第0层开始依次往后，next指向下面一个节点，然后释放前面一个节点，
      // 释放完之后，node再次指向next所指向的节点，然后进入下一轮询，最后全部释放
      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. */
  /**
   * 随机生成层高level，这个层高可能比原来的高
   * @return
   */
  int zslRandomLevel(void) {
      int level = 1;
      while ((random()&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'. */
  /**
   * 跳表插入一个节点
   * 参照图解：https://wiki.jikexueyuan.com/project/redis/skiplist.html
   * 这个博文的图示比较细致，可以参考
   * @param zsl
   * @param score
   * @param ele
   * @return
   */
  zskiplistNode *zslInsert(zskiplist *zsl, double score, sds ele) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      unsigned int rank[ZSKIPLIST_MAXLEVEL];
      int i, level;
  
      serverAssert(!isnan(score));
      x = zsl->header;//x指向头节点
      //从最高层开始扫描
      for (i = zsl->level-1; i >= 0; i--) {
          /* store rank that is crossed to reach the insert position */
          //上方英文解释很清楚，rank数组里放的是从头节点到插入点的跨度
          rank[i] = i == (zsl->level-1) ? 0 : rank[i+1];
          /**
           * 沿着头节点，安装forward指针的方向一路比较，如果当前节点score<待插入节点的score，
           * 或者socre相等，则比较ele元素的字典大小，如果当前节点ele字典大小<待插入节点的ele值。
           *
           * 则继续向前比较，每次比较后rank[i]做跨度累加，x指针forward方向位移，这样一直位移到待插入位置
           * update[i]表示待插入位置的节点，rank[i]表示头结点到待插入节点的跨度。
           *
           */
          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. */
      /**
       * 如果插入节点的层高比当前跳表的层高还要高，
       * 这时候需要对额外高出的层做设置
       */
      level = zslRandomLevel();
      if (level > zsl->level) {
          //循环对高出的层做设置，例如新节点层高是5(level[0]...level[4])，当前跳表层高是2(level[0]-level[1])，
          //那么就对level[2].level[3].level[4]这三层做设置
          for (i = zsl->level; i < level; i++) {
              rank[i] = 0;//只有头节点，所以rank[i]是0
              update[i] = zsl->header;//插入位置只能是头节点后面
              update[i]->level[i].span = zsl->length;//头节点的跨度设置为当前跳表长度（后续会重新计算）
          }
          zsl->level = level;//将最高层数赋值给当前跳表的层高
      }
      //开始新建这个节点，预备插入（前面的过程都是在找插入位置）
      x = zslCreateNode(level,score,ele);
      /**
       * 从最底层开始一次往上一层一层的插入（插入操作实际就是普通链表插入操作）
       * 新节点xforward指针指向update节点forward所指向的节点，然后让update节点forward指向x节点(典型的链表插入)
       *
       */
      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 */
          /**
           * 这部分不太容易理解（借助于图示理解）
           * update节点到下个节点的跨度是update[i]->level[i].span。此时x节点要插入到update节点之后
           * 那么就是相当于x到下个节点的跨度就是update[i]->level[i].span减去某段距离（肯定是跨度更小了）
           * 那么究竟小多少？？
           * 就是rank[0] - rank[i]：这段的意思是最底层待插入节点的跨度减去每一层待插入节点的跨度，这就是多
           * 出来的，所以要减掉
           *
           * 250行的计算全式应该是这样的（https://blog.csdn.net/u013536232/article/details/105476382）
           * 示意图：假如，8，9,10，11,12.在9,10直接插入9.5
           * 8------------------------------------------------------------------12   level2
           * 8--------------------------9.5------------------------11-----------12   level1
           * 8------------9-------------9.5-----------10-----------11-----------12   level0
           * 解释：
           * 一、等号左边
           * 1表示9-9.5之间的跨度（也就是1个节点的跨度）
           * update[i]->level[i].span表示插入点8到12之间的跨度（level1是8-12跨度，level0是9-12跨度）
           *
           * 二、等号右边
           * 假如是level0，那么就是rank[0]表示9节点到header之间的跨度，rank[i]这时候i=0,所以
           * rank[0] - rank[i]=0
           * 1表示9-9.5直接的跨度
           * x->level[i].span表示新增节点x到12之间的跨度
           *
           * (update[i]->level[i].span)+1=(rank[0] - rank[i])+1+(x->level[i].span)
           * 所以继续往下演变成  |
           *                 |
           *                \/                                           */
          x->level[i].span = update[i]->level[i].span - (rank[0] - rank[i]);
          //update[i]->level[i].span相当于是update节点到x节点的跨度
          update[i]->level[i].span = (rank[0] - rank[i]) + 1;
      }
  
      /* increment span for untouched levels */
      /**
       * 所有未涉及到的level都应该在对应的update[i]节点后面加1（以为下面层里都已经相当于多了1个节点了）
       * 还以上图为例子。假如层高是2，则第三层（level2实际9.5没有插入），但是从update[i]=8这个节点往后的
       * span都应该+1
       */
      for (i = level; i < zsl->level; i++) {
          update[i]->level[i].span++;
      }
  
      //设置后向指针：x新节点的后向指针指向update[i](新节点的前一个)；
      x->backward = (update[0] == zsl->header) ? NULL : update[0];
      //如果新节点不是在尾部插入的，那么他的后面一个节点的后向指针指向新节点x
      if (x->level[0].forward)
          x->level[0].forward->backward = x;
      //如果是在尾部插入
      else
          //直接将尾指针指向x
          zsl->tail = x;
      //全部搞定，跳表长度+1
      zsl->length++;
      return x;
  }
  
  /* Internal function used by zslDelete, zslDeleteRangeByScore and
   * zslDeleteRangeByRank. */
  /**
   * 指定删除x节点
   * @param zsl
   * @param x
   * @param update
   */
  void zslDeleteNode(zskiplist *zsl, zskiplistNode *x, zskiplistNode **update) {
      int i;
      for (i = 0; i < zsl->level; i++) {
          /**
           * 扫描每一层，如果update[i]的下一个节点正好是要删除的x，那么
           * 假如要删除9.5，如下示意图：
           *
           * 8----------9----------9.5---------10--------11
           *
           * 那么9就是update[i],9.5就是x，去除9.5之后的update的新span就是 update[i]+x-1
           * 这个1就是9.5的跨度，现在删除了，那么跨度就减去1
           * 后把x节点后面的节点赋值给update的forward，相当于从9--》指向10了
           */
          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 {
              //这里的逻辑和插入节点那里高出9.5层高的思路是一样的，新增是++，那么这里删除就是--
              update[i]->level[i].span -= 1;
          }
      }
      /**
       * 设置后向指针
       */
      if (x->level[0].forward) {
          //x前向节点的后向指针指向x的后向指针（x的后向指针指向的是x的前面一个节点，也就是跨过x了）
          x->level[0].forward->backward = x->backward;
      } else {
          //如果x是尾节点，则tail指针指向x前面一个节点（这个节点此时就是尾节点了）
          zsl->tail = x->backward;
      }
      //头节点后面已经没有节点了（forward指向null），则这层可以去掉了，所以zsl->level--
      while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
          zsl->level--;
      //删除完跳表长度-1
      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;
      /**
       * 每层开始从头节点开始查找，找到要删除的节点的前一个节点，存入update[i]
       * 后续要设置他们的span和forward
       */
      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) {
          //找到这个x节点之后开始删除
          zslDeleteNode(zsl, x, update);
          if (!node)
              zslFreeNode(x);//释放x节点的内存空间
          else
              *node = x;
          return 1;
      }
      return 0; /* not found */
  }
  
  /* Update the score of an elmenent inside the sorted set skiplist.
   * Note that the element must exist and must match 'score'.
   * This function does not update the score in the hash table side, the
   * caller should take care of it.
   *
   * Note that this function attempts to just update the node, in case after
   * the score update, the node would be exactly at the same position.
   * Otherwise the skiplist is modified by removing and re-adding a new
   * element, which is more costly.
   *
   * The function returns the updated element skiplist node pointer. */
  zskiplistNode *zslUpdateScore(zskiplist *zsl, double curscore, sds ele, double newscore) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      int i;
  
      /* We need to seek to element to update to start: this is useful anyway,
       * we'll have to update or remove it. */
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward &&
                  (x->level[i].forward->score < curscore ||
                      (x->level[i].forward->score == curscore &&
                       sdscmp(x->level[i].forward->ele,ele) < 0)))
          {
              x = x->level[i].forward;
          }
          update[i] = x;
      }
  
      /* Jump to our element: note that this function assumes that the
       * element with the matching score exists. */
      x = x->level[0].forward;
      serverAssert(x && curscore == x->score && sdscmp(x->ele,ele) == 0);
  
      /* If the node, after the score update, would be still exactly
       * at the same position, we can just update the score without
       * actually removing and re-inserting the element in the skiplist. */
      if ((x->backward == NULL || x->backward->score < newscore) &&
          (x->level[0].forward == NULL || x->level[0].forward->score > newscore))
      {
          x->score = newscore;
          return x;
      }
  
      /* No way to reuse the old node: we need to remove and insert a new
       * one at a different place. */
      zslDeleteNode(zsl, x, update);
      zskiplistNode *newnode = zslInsert(zsl,newscore,x->ele);
      /* We reused the old node x->ele SDS string, free the node now
       * since zslInsert created a new one. */
      x->ele = NULL;
      zslFreeNode(x);
      return newnode;
  }
  
  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;
      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. */
  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. */
      serverAssert(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. */
  static 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 comparison, 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 = shared.maxstring;
          return C_OK;
      case '-':
          if (c[1] != '\0') return C_ERR;
          *ex = 1;
          *dest = shared.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) {
      if (spec->min != shared.minstring &&
          spec->min != shared.maxstring) sdsfree(spec->min);
      if (spec->max != shared.minstring &&
          spec->max != shared.maxstring) 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;
      if (a == shared.minstring || b == shared.maxstring) return -1;
      if (a == shared.maxstring || b == shared.minstring) return 1;
      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;
      serverAssert(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. */
      serverAssert(x != NULL);
  
      /* Check if score >= min. */
      if (!zslLexValueGteMin(x->ele,range)) return NULL;
      return x;
  }
  
  /*-----------------------------------------------------------------------------
   * Ziplist-backed sorted set API
   *----------------------------------------------------------------------------*/
  
  double zzlGetScore(unsigned char *sptr) {
      unsigned char *vstr;
      unsigned int vlen;
      long long vlong;
      char buf[128];
      double score;
  
      serverAssert(sptr != NULL);
      serverAssert(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;
  
      serverAssert(sptr != NULL);
      serverAssert(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;
  
      serverAssert(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;
  }
  
  unsigned int zzlLength(unsigned char *zl) {
      return ziplistLen(zl)/2;
  }
  
  /* 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;
      serverAssert(*eptr != NULL && *sptr != NULL);
  
      _eptr = ziplistNext(zl,*sptr);
      if (_eptr != NULL) {
          _sptr = ziplistNext(zl,_eptr);
          serverAssert(_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;
      serverAssert(*eptr != NULL && *sptr != NULL);
  
      _sptr = ziplistPrev(zl,*eptr);
      if (_sptr != NULL) {
          _eptr = ziplistPrev(zl,_sptr);
          serverAssert(_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. */
      serverAssert(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);
          serverAssert(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);
          serverAssert(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)
              serverAssert((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. */
      serverAssert(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. */
          serverAssert(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)
              serverAssert((eptr = ziplistPrev(zl,sptr)) != NULL);
          else
              eptr = NULL;
      }
  
      return NULL;
  }
  
  unsigned char *zzlFind(unsigned char *zl, sds ele, double *score) {
      unsigned char *eptr = ziplistIndex(zl,0), *sptr;
  
      while (eptr != NULL) {
          sptr = ziplistNext(zl,eptr);
          serverAssert(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;
  }
  
  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. */
          serverAssert((sptr = ziplistNext(zl,eptr)) != NULL);
          zl = ziplistInsert(zl,sptr,(unsigned char*)scorebuf,scorelen);
      }
      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);
          serverAssert(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 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 long zsetLength(const robj *zobj) {
      unsigned long length = 0;
      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)
              serverPanic("Unknown target encoding");
  
          zs = zmalloc(sizeof(*zs));
          zs->dict = dictCreate(&zsetDictType,NULL);
          zs->zsl = zslCreate();
  
          eptr = ziplistIndex(zl,0);
          serverAssertWithInfo(NULL,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
          serverAssertWithInfo(NULL,zobj,sptr != NULL);
  
          while (eptr != NULL) {
              score = zzlGetScore(sptr);
              serverAssertWithInfo(NULL,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
              if (vstr == NULL)
                  ele = sdsfromlonglong(vlong);
              else
                  ele = sdsnewlen((char*)vstr,vlen);
  
              node = zslInsert(zs->zsl,score,ele);
              serverAssert(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)
              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 <= server.zset_max_ziplist_entries &&
          maxelelen <= server.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 error, currently only when the increment
   * produces a NAN condition, or when the 'score' value is NAN since the
   * start.
   *
   * The command as a side effect of adding a new element may convert the sorted
   * set internal encoding from ziplist to hashtable+skiplist.
   *
   * Memory management 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) > server.zset_max_ziplist_entries ||
                  sdslen(ele) > server.zset_max_ziplist_value)
                  zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);//压缩列表转换为跳跃表
              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) {
                  znode = zslUpdateScore(zs->zsl,curscore,ele,score);
                  /* 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);
              serverAssert(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);
              serverAssert(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);
          serverAssert(eptr != NULL);
          sptr = ziplistNext(zl,eptr);
          serverAssert(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. */
              serverAssert(rank != 0);
              if (reverse)
                  return llen-rank;
              else
                  return rank-1;
          } else {
              return -1;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  }
  
  /*-----------------------------------------------------------------------------
   * Sorted set commands
   *----------------------------------------------------------------------------*/
  
  /* This generic command implements both ZADD and ZINCRBY. */
  void zaddGenericCommand(client *c, int flags) {
      static char *nanerr = "resulting score is not a number (NaN)";
      robj *key = c->argv[1];
      robj *zobj;
      sds ele;
      double score = 0, *scores = NULL;
      int j, elements;
      int scoreidx = 0;
      /* The following vars are used in order to track what the command actually
       * did during the execution, to reply to the client and to trigger the
       * notification of keyspace change. */
      int added = 0;      /* Number of new elements added. */
      int updated = 0;    /* Number of elements with updated score. */
      int processed = 0;  /* Number of elements processed, may remain zero with
                             options like XX. */
  
      /* Parse options. At the end 'scoreidx' is set to the argument position
       * of the score of the first score-element pair. */
      scoreidx = 2;
      while(scoreidx < c->argc) {
          char *opt = c->argv[scoreidx]->ptr;
          if (!strcasecmp(opt,"nx")) flags |= ZADD_NX;
          else if (!strcasecmp(opt,"xx")) flags |= ZADD_XX;
          else if (!strcasecmp(opt,"ch")) flags |= ZADD_CH;
          else if (!strcasecmp(opt,"incr")) flags |= ZADD_INCR;
          else break;
          scoreidx++;
      }
  
      /* 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;
      int ch = (flags & ZADD_CH) != 0;
  
      /* After the options, we expect to have an even number of args, since
       * we expect any number of score-element pairs. */
      elements = c->argc-scoreidx;
      if (elements % 2 || !elements) {
          addReply(c,shared.syntaxerr);
          return;
      }
      elements /= 2; /* Now this holds the number of score-element pairs. */
  
      /* Check for incompatible options. */
      if (nx && xx) {
          addReplyError(c,
              "XX and NX options at the same time are not compatible");
          return;
      }
  
      if (incr && elements > 1) {
          addReplyError(c,
              "INCR option supports a single increment-element pair");
          return;
      }
  
      /* Start parsing all the scores, we need to emit any syntax error
       * before executing additions to the sorted set, as the command should
       * either execute fully or nothing at all. */
      scores = zmalloc(sizeof(double)*elements);
      for (j = 0; j < elements; j++) {
          if (getDoubleFromObjectOrReply(c,c->argv[scoreidx+j*2],&scores[j],NULL)
              != C_OK) goto cleanup;
      }
  
      /* Lookup the key and create the sorted set if does not exist. */
      zobj = lookupKeyWrite(c->db,key);
      if (zobj == NULL) {
          if (xx) goto reply_to_client; /* No key + XX option: nothing to do. */
          if (server.zset_max_ziplist_entries == 0 ||
              server.zset_max_ziplist_value < sdslen(c->argv[scoreidx+1]->ptr))
          {
              zobj = createZsetObject();//创建的跳跃表结构
          } else {
              zobj = createZsetZiplistObject();//创建的压缩表结构
          }
          dbAdd(c->db,key,zobj);
      } else {
          if (zobj->type != OBJ_ZSET) {
              addReply(c,shared.wrongtypeerr);
              goto cleanup;
          }
      }
  
      for (j = 0; j < elements; j++) {
          double newscore;
          score = scores[j];
          int retflags = flags;
  
          ele = c->argv[scoreidx+1+j*2]->ptr;
          int retval = zsetAdd(zobj, score, ele, &retflags, &newscore);
          if (retval == 0) {
              addReplyError(c,nanerr);
              goto cleanup;
          }
          if (retflags & ZADD_ADDED) added++;
          if (retflags & ZADD_UPDATED) updated++;
          if (!(retflags & ZADD_NOP)) processed++;
          score = newscore;
      }
      server.dirty += (added+updated);
  
  reply_to_client:
      if (incr) { /* ZINCRBY or INCR option. */
          if (processed)
              addReplyDouble(c,score);
          else
              addReplyNull(c);
      } else { /* ZADD. */
          addReplyLongLong(c,ch ? added+updated : added);
      }
  
  cleanup:
      zfree(scores);
      if (added || updated) {
          signalModifiedKey(c,c->db,key);
          notifyKeyspaceEvent(NOTIFY_ZSET,
              incr ? "zincr" : "zadd", key, c->db->id);
      }
  }
  
  void zaddCommand(client *c) {
      zaddGenericCommand(c,ZADD_NONE);
  }
  
  void zincrbyCommand(client *c) {
      zaddGenericCommand(c,ZADD_INCR);
  }
  
  void zremCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      int deleted = 0, keyremoved = 0, j;
  
      if ((zobj = lookupKeyWriteOrReply(c,key,shared.czero)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      for (j = 2; j < c->argc; j++) {
          if (zsetDel(zobj,c->argv[j]->ptr)) deleted++;
          if (zsetLength(zobj) == 0) {
              dbDelete(c->db,key);
              keyremoved = 1;
              break;
          }
      }
  
      if (deleted) {
          notifyKeyspaceEvent(NOTIFY_ZSET,"zrem",key,c->db->id);
          if (keyremoved)
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
          signalModifiedKey(c,c->db,key);
          server.dirty += deleted;
      }
      addReplyLongLong(c,deleted);
  }
  
  /* Implements ZREMRANGEBYRANK, ZREMRANGEBYSCORE, ZREMRANGEBYLEX commands. */
  #define ZRANGE_RANK 0
  #define ZRANGE_SCORE 1
  #define ZRANGE_LEX 2
  void zremrangeGenericCommand(client *c, int rangetype) {
      robj *key = c->argv[1];
      robj *zobj;
      int keyremoved = 0;
      unsigned long deleted = 0;
      zrangespec range;
      zlexrangespec lexrange;
      long start, end, llen;
  
      /* Step 1: Parse the range. */
      if (rangetype == ZRANGE_RANK) {
          if ((getLongFromObjectOrReply(c,c->argv[2],&start,NULL) != C_OK) ||
              (getLongFromObjectOrReply(c,c->argv[3],&end,NULL) != C_OK))
              return;
      } else if (rangetype == ZRANGE_SCORE) {
          if (zslParseRange(c->argv[2],c->argv[3],&range) != C_OK) {
              addReplyError(c,"min or max is not a float");
              return;
          }
      } else if (rangetype == ZRANGE_LEX) {
          if (zslParseLexRange(c->argv[2],c->argv[3],&lexrange) != C_OK) {
              addReplyError(c,"min or max not valid string range item");
              return;
          }
      }
  
      /* Step 2: Lookup & range sanity checks if needed. */
      if ((zobj = lookupKeyWriteOrReply(c,key,shared.czero)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) goto cleanup;
  
      if (rangetype == ZRANGE_RANK) {
          /* Sanitize indexes. */
          llen = zsetLength(zobj);
          if (start < 0) start = llen+start;
          if (end < 0) end = llen+end;
          if (start < 0) start = 0;
  
          /* Invariant: start >= 0, so this test will be true when end < 0.
           * The range is empty when start > end or start >= length. */
          if (start > end || start >= llen) {
              addReply(c,shared.czero);
              goto cleanup;
          }
          if (end >= llen) end = llen-1;
      }
  
      /* Step 3: Perform the range deletion operation. */
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          switch(rangetype) {
          case ZRANGE_RANK:
              zobj->ptr = zzlDeleteRangeByRank(zobj->ptr,start+1,end+1,&deleted);
              break;
          case ZRANGE_SCORE:
              zobj->ptr = zzlDeleteRangeByScore(zobj->ptr,&range,&deleted);
              break;
          case ZRANGE_LEX:
              zobj->ptr = zzlDeleteRangeByLex(zobj->ptr,&lexrange,&deleted);
              break;
          }
          if (zzlLength(zobj->ptr) == 0) {
              dbDelete(c->db,key);
              keyremoved = 1;
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          switch(rangetype) {
          case ZRANGE_RANK:
              deleted = zslDeleteRangeByRank(zs->zsl,start+1,end+1,zs->dict);
              break;
          case ZRANGE_SCORE:
              deleted = zslDeleteRangeByScore(zs->zsl,&range,zs->dict);
              break;
          case ZRANGE_LEX:
              deleted = zslDeleteRangeByLex(zs->zsl,&lexrange,zs->dict);
              break;
          }
          if (htNeedsResize(zs->dict)) dictResize(zs->dict);
          if (dictSize(zs->dict) == 0) {
              dbDelete(c->db,key);
              keyremoved = 1;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      /* Step 4: Notifications and reply. */
      if (deleted) {
          char *event[3] = {"zremrangebyrank","zremrangebyscore","zremrangebylex"};
          signalModifiedKey(c,c->db,key);
          notifyKeyspaceEvent(NOTIFY_ZSET,event[rangetype],key,c->db->id);
          if (keyremoved)
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
      }
      server.dirty += deleted;
      addReplyLongLong(c,deleted);
  
  cleanup:
      if (rangetype == ZRANGE_LEX) zslFreeLexRange(&lexrange);
  }
  
  void zremrangebyrankCommand(client *c) {
      zremrangeGenericCommand(c,ZRANGE_RANK);
  }
  
  void zremrangebyscoreCommand(client *c) {
      zremrangeGenericCommand(c,ZRANGE_SCORE);
  }
  
  void zremrangebylexCommand(client *c) {
      zremrangeGenericCommand(c,ZRANGE_LEX);
  }
  
  typedef struct {
      robj *subject;
      int type; /* Set, sorted set */
      int encoding;
      double weight;
  
      union {
          /* Set iterators. */
          union _iterset {
              struct {
                  intset *is;
                  int ii;
              } is;
              struct {
                  dict *dict;
                  dictIterator *di;
                  dictEntry *de;
              } ht;
          } set;
  
          /* Sorted set iterators. */
          union _iterzset {
              struct {
                  unsigned char *zl;
                  unsigned char *eptr, *sptr;
              } zl;
              struct {
                  zset *zs;
                  zskiplistNode *node;
              } sl;
          } zset;
      } iter;
  } zsetopsrc;
  
  
  /* Use dirty flags for pointers that need to be cleaned up in the next
   * iteration over the zsetopval. The dirty flag for the long long value is
   * special, since long long values don't need cleanup. Instead, it means that
   * we already checked that "ell" holds a long long, or tried to convert another
   * representation into a long long value. When this was successful,
   * OPVAL_VALID_LL is set as well. */
  #define OPVAL_DIRTY_SDS 1
  #define OPVAL_DIRTY_LL 2
  #define OPVAL_VALID_LL 4
  
  /* Store value retrieved from the iterator. */
  typedef struct {
      int flags;
      unsigned char _buf[32]; /* Private buffer. */
      sds ele;
      unsigned char *estr;
      unsigned int elen;
      long long ell;
      double score;
  } zsetopval;
  
  typedef union _iterset iterset;
  typedef union _iterzset iterzset;
  
  void zuiInitIterator(zsetopsrc *op) {
      if (op->subject == NULL)
          return;
  
      if (op->type == OBJ_SET) {
          iterset *it = &op->iter.set;
          if (op->encoding == OBJ_ENCODING_INTSET) {
              it->is.is = op->subject->ptr;
              it->is.ii = 0;
          } else if (op->encoding == OBJ_ENCODING_HT) {
              it->ht.dict = op->subject->ptr;
              it->ht.di = dictGetIterator(op->subject->ptr);
              it->ht.de = dictNext(it->ht.di);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          iterzset *it = &op->iter.zset;
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              it->zl.zl = op->subject->ptr;
              it->zl.eptr = ziplistIndex(it->zl.zl,0);
              if (it->zl.eptr != NULL) {
                  it->zl.sptr = ziplistNext(it->zl.zl,it->zl.eptr);
                  serverAssert(it->zl.sptr != NULL);
              }
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              it->sl.zs = op->subject->ptr;
              it->sl.node = it->sl.zs->zsl->header->level[0].forward;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  void zuiClearIterator(zsetopsrc *op) {
      if (op->subject == NULL)
          return;
  
      if (op->type == OBJ_SET) {
          iterset *it = &op->iter.set;
          if (op->encoding == OBJ_ENCODING_INTSET) {
              UNUSED(it); /* skip */
          } else if (op->encoding == OBJ_ENCODING_HT) {
              dictReleaseIterator(it->ht.di);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          iterzset *it = &op->iter.zset;
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              UNUSED(it); /* skip */
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              UNUSED(it); /* skip */
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  unsigned long zuiLength(zsetopsrc *op) {
      if (op->subject == NULL)
          return 0;
  
      if (op->type == OBJ_SET) {
          if (op->encoding == OBJ_ENCODING_INTSET) {
              return intsetLen(op->subject->ptr);
          } else if (op->encoding == OBJ_ENCODING_HT) {
              dict *ht = op->subject->ptr;
              return dictSize(ht);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              return zzlLength(op->subject->ptr);
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              zset *zs = op->subject->ptr;
              return zs->zsl->length;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  /* Check if the current value is valid. If so, store it in the passed structure
   * and move to the next element. If not valid, this means we have reached the
   * end of the structure and can abort. */
  int zuiNext(zsetopsrc *op, zsetopval *val) {
      if (op->subject == NULL)
          return 0;
  
      if (val->flags & OPVAL_DIRTY_SDS)
          sdsfree(val->ele);
  
      memset(val,0,sizeof(zsetopval));
  
      if (op->type == OBJ_SET) {
          iterset *it = &op->iter.set;
          if (op->encoding == OBJ_ENCODING_INTSET) {
              int64_t ell;
  
              if (!intsetGet(it->is.is,it->is.ii,&ell))
                  return 0;
              val->ell = ell;
              val->score = 1.0;
  
              /* Move to next element. */
              it->is.ii++;
          } else if (op->encoding == OBJ_ENCODING_HT) {
              if (it->ht.de == NULL)
                  return 0;
              val->ele = dictGetKey(it->ht.de);
              val->score = 1.0;
  
              /* Move to next element. */
              it->ht.de = dictNext(it->ht.di);
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          iterzset *it = &op->iter.zset;
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              /* No need to check both, but better be explicit. */
              if (it->zl.eptr == NULL || it->zl.sptr == NULL)
                  return 0;
              serverAssert(ziplistGet(it->zl.eptr,&val->estr,&val->elen,&val->ell));
              val->score = zzlGetScore(it->zl.sptr);
  
              /* Move to next element. */
              zzlNext(it->zl.zl,&it->zl.eptr,&it->zl.sptr);
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              if (it->sl.node == NULL)
                  return 0;
              val->ele = it->sl.node->ele;
              val->score = it->sl.node->score;
  
              /* Move to next element. */
              it->sl.node = it->sl.node->level[0].forward;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
      return 1;
  }
  
  int zuiLongLongFromValue(zsetopval *val) {
      if (!(val->flags & OPVAL_DIRTY_LL)) {
          val->flags |= OPVAL_DIRTY_LL;
  
          if (val->ele != NULL) {
              if (string2ll(val->ele,sdslen(val->ele),&val->ell))
                  val->flags |= OPVAL_VALID_LL;
          } else if (val->estr != NULL) {
              if (string2ll((char*)val->estr,val->elen,&val->ell))
                  val->flags |= OPVAL_VALID_LL;
          } else {
              /* The long long was already set, flag as valid. */
              val->flags |= OPVAL_VALID_LL;
          }
      }
      return val->flags & OPVAL_VALID_LL;
  }
  
  sds zuiSdsFromValue(zsetopval *val) {
      if (val->ele == NULL) {
          if (val->estr != NULL) {
              val->ele = sdsnewlen((char*)val->estr,val->elen);
          } else {
              val->ele = sdsfromlonglong(val->ell);
          }
          val->flags |= OPVAL_DIRTY_SDS;
      }
      return val->ele;
  }
  
  /* This is different from zuiSdsFromValue since returns a new SDS string
   * which is up to the caller to free. */
  sds zuiNewSdsFromValue(zsetopval *val) {
      if (val->flags & OPVAL_DIRTY_SDS) {
          /* We have already one to return! */
          sds ele = val->ele;
          val->flags &= ~OPVAL_DIRTY_SDS;
          val->ele = NULL;
          return ele;
      } else if (val->ele) {
          return sdsdup(val->ele);
      } else if (val->estr) {
          return sdsnewlen((char*)val->estr,val->elen);
      } else {
          return sdsfromlonglong(val->ell);
      }
  }
  
  int zuiBufferFromValue(zsetopval *val) {
      if (val->estr == NULL) {
          if (val->ele != NULL) {
              val->elen = sdslen(val->ele);
              val->estr = (unsigned char*)val->ele;
          } else {
              val->elen = ll2string((char*)val->_buf,sizeof(val->_buf),val->ell);
              val->estr = val->_buf;
          }
      }
      return 1;
  }
  
  /* Find value pointed to by val in the source pointer to by op. When found,
   * return 1 and store its score in target. Return 0 otherwise. */
  int zuiFind(zsetopsrc *op, zsetopval *val, double *score) {
      if (op->subject == NULL)
          return 0;
  
      if (op->type == OBJ_SET) {
          if (op->encoding == OBJ_ENCODING_INTSET) {
              if (zuiLongLongFromValue(val) &&
                  intsetFind(op->subject->ptr,val->ell))
              {
                  *score = 1.0;
                  return 1;
              } else {
                  return 0;
              }
          } else if (op->encoding == OBJ_ENCODING_HT) {
              dict *ht = op->subject->ptr;
              zuiSdsFromValue(val);
              if (dictFind(ht,val->ele) != NULL) {
                  *score = 1.0;
                  return 1;
              } else {
                  return 0;
              }
          } else {
              serverPanic("Unknown set encoding");
          }
      } else if (op->type == OBJ_ZSET) {
          zuiSdsFromValue(val);
  
          if (op->encoding == OBJ_ENCODING_ZIPLIST) {
              if (zzlFind(op->subject->ptr,val->ele,score) != NULL) {
                  /* Score is already set by zzlFind. */
                  return 1;
              } else {
                  return 0;
              }
          } else if (op->encoding == OBJ_ENCODING_SKIPLIST) {
              zset *zs = op->subject->ptr;
              dictEntry *de;
              if ((de = dictFind(zs->dict,val->ele)) != NULL) {
                  *score = *(double*)dictGetVal(de);
                  return 1;
              } else {
                  return 0;
              }
          } else {
              serverPanic("Unknown sorted set encoding");
          }
      } else {
          serverPanic("Unsupported type");
      }
  }
  
  int zuiCompareByCardinality(const void *s1, const void *s2) {
      unsigned long first = zuiLength((zsetopsrc*)s1);
      unsigned long second = zuiLength((zsetopsrc*)s2);
      if (first > second) return 1;
      if (first < second) return -1;
      return 0;
  }
  
  #define REDIS_AGGR_SUM 1
  #define REDIS_AGGR_MIN 2
  #define REDIS_AGGR_MAX 3
  #define zunionInterDictValue(_e) (dictGetVal(_e) == NULL ? 1.0 : *(double*)dictGetVal(_e))
  
  inline static void zunionInterAggregate(double *target, double val, int aggregate) {
      if (aggregate == REDIS_AGGR_SUM) {
          *target = *target + val;
          /* The result of adding two doubles is NaN when one variable
           * is +inf and the other is -inf. When these numbers are added,
           * we maintain the convention of the result being 0.0. */
          if (isnan(*target)) *target = 0.0;
      } else if (aggregate == REDIS_AGGR_MIN) {
          *target = val < *target ? val : *target;
      } else if (aggregate == REDIS_AGGR_MAX) {
          *target = val > *target ? val : *target;
      } else {
          /* safety net */
          serverPanic("Unknown ZUNION/INTER aggregate type");
      }
  }
  
  uint64_t dictSdsHash(const void *key);
  int dictSdsKeyCompare(void *privdata, const void *key1, const void *key2);
  
  dictType setAccumulatorDictType = {
      dictSdsHash,               /* hash function */
      NULL,                      /* key dup */
      NULL,                      /* val dup */
      dictSdsKeyCompare,         /* key compare */
      NULL,                      /* key destructor */
      NULL                       /* val destructor */
  };
  
  void zunionInterGenericCommand(client *c, robj *dstkey, int op) {
      int i, j;
      long setnum;
      int aggregate = REDIS_AGGR_SUM;
      zsetopsrc *src;
      zsetopval zval;
      sds tmp;
      size_t maxelelen = 0;
      robj *dstobj;
      zset *dstzset;
      zskiplistNode *znode;
      int touched = 0;
  
      /* expect setnum input keys to be given */
      if ((getLongFromObjectOrReply(c, c->argv[2], &setnum, NULL) != C_OK))
          return;
  
      if (setnum < 1) {
          addReplyError(c,
              "at least 1 input key is needed for ZUNIONSTORE/ZINTERSTORE");
          return;
      }
  
      /* test if the expected number of keys would overflow */
      if (setnum > c->argc-3) {
          addReply(c,shared.syntaxerr);
          return;
      }
  
      /* read keys to be used for input */
      src = zcalloc(sizeof(zsetopsrc) * setnum);
      for (i = 0, j = 3; i < setnum; i++, j++) {
          robj *obj = lookupKeyWrite(c->db,c->argv[j]);
          if (obj != NULL) {
              if (obj->type != OBJ_ZSET && obj->type != OBJ_SET) {
                  zfree(src);
                  addReply(c,shared.wrongtypeerr);
                  return;
              }
  
              src[i].subject = obj;
              src[i].type = obj->type;
              src[i].encoding = obj->encoding;
          } else {
              src[i].subject = NULL;
          }
  
          /* Default all weights to 1. */
          src[i].weight = 1.0;
      }
  
      /* parse optional extra arguments */
      if (j < c->argc) {
          int remaining = c->argc - j;
  
          while (remaining) {
              if (remaining >= (setnum + 1) &&
                  !strcasecmp(c->argv[j]->ptr,"weights"))
              {
                  j++; remaining--;
                  for (i = 0; i < setnum; i++, j++, remaining--) {
                      if (getDoubleFromObjectOrReply(c,c->argv[j],&src[i].weight,
                              "weight value is not a float") != C_OK)
                      {
                          zfree(src);
                          return;
                      }
                  }
              } else if (remaining >= 2 &&
                         !strcasecmp(c->argv[j]->ptr,"aggregate"))
              {
                  j++; remaining--;
                  if (!strcasecmp(c->argv[j]->ptr,"sum")) {
                      aggregate = REDIS_AGGR_SUM;
                  } else if (!strcasecmp(c->argv[j]->ptr,"min")) {
                      aggregate = REDIS_AGGR_MIN;
                  } else if (!strcasecmp(c->argv[j]->ptr,"max")) {
                      aggregate = REDIS_AGGR_MAX;
                  } else {
                      zfree(src);
                      addReply(c,shared.syntaxerr);
                      return;
                  }
                  j++; remaining--;
              } else {
                  zfree(src);
                  addReply(c,shared.syntaxerr);
                  return;
              }
          }
      }
  
      /* sort sets from the smallest to largest, this will improve our
       * algorithm's performance */
      qsort(src,setnum,sizeof(zsetopsrc),zuiCompareByCardinality);
  
      dstobj = createZsetObject();
      dstzset = dstobj->ptr;
      memset(&zval, 0, sizeof(zval));
  
      if (op == SET_OP_INTER) {
          /* Skip everything if the smallest input is empty. */
          if (zuiLength(&src[0]) > 0) {
              /* Precondition: as src[0] is non-empty and the inputs are ordered
               * by size, all src[i > 0] are non-empty too. */
              zuiInitIterator(&src[0]);
              while (zuiNext(&src[0],&zval)) {
                  double score, value;
  
                  score = src[0].weight * zval.score;
                  if (isnan(score)) score = 0;
  
                  for (j = 1; j < setnum; j++) {
                      /* It is not safe to access the zset we are
                       * iterating, so explicitly check for equal object. */
                      if (src[j].subject == src[0].subject) {
                          value = zval.score*src[j].weight;
                          zunionInterAggregate(&score,value,aggregate);
                      } else if (zuiFind(&src[j],&zval,&value)) {
                          value *= src[j].weight;
                          zunionInterAggregate(&score,value,aggregate);
                      } else {
                          break;
                      }
                  }
  
                  /* Only continue when present in every input. */
                  if (j == setnum) {
                      tmp = zuiNewSdsFromValue(&zval);
                      znode = zslInsert(dstzset->zsl,score,tmp);
                      dictAdd(dstzset->dict,tmp,&znode->score);
                      if (sdslen(tmp) > maxelelen) maxelelen = sdslen(tmp);
                  }
              }
              zuiClearIterator(&src[0]);
          }
      } else if (op == SET_OP_UNION) {
          dict *accumulator = dictCreate(&setAccumulatorDictType,NULL);
          dictIterator *di;
          dictEntry *de, *existing;
          double score;
  
          if (setnum) {
              /* Our union is at least as large as the largest set.
               * Resize the dictionary ASAP to avoid useless rehashing. */
              dictExpand(accumulator,zuiLength(&src[setnum-1]));
          }
  
          /* Step 1: Create a dictionary of elements -> aggregated-scores
           * by iterating one sorted set after the other. */
          for (i = 0; i < setnum; i++) {
              if (zuiLength(&src[i]) == 0) continue;
  
              zuiInitIterator(&src[i]);
              while (zuiNext(&src[i],&zval)) {
                  /* Initialize value */
                  score = src[i].weight * zval.score;
                  if (isnan(score)) score = 0;
  
                  /* Search for this element in the accumulating dictionary. */
                  de = dictAddRaw(accumulator,zuiSdsFromValue(&zval),&existing);
                  /* If we don't have it, we need to create a new entry. */
                  if (!existing) {
                      tmp = zuiNewSdsFromValue(&zval);
                      /* Remember the longest single element encountered,
                       * to understand if it's possible to convert to ziplist
                       * at the end. */
                       if (sdslen(tmp) > maxelelen) maxelelen = sdslen(tmp);
                      /* Update the element with its initial score. */
                      dictSetKey(accumulator, de, tmp);
                      dictSetDoubleVal(de,score);
                  } else {
                      /* Update the score with the score of the new instance
                       * of the element found in the current sorted set.
                       *
                       * Here we access directly the dictEntry double
                       * value inside the union as it is a big speedup
                       * compared to using the getDouble/setDouble API. */
                      zunionInterAggregate(&existing->v.d,score,aggregate);
                  }
              }
              zuiClearIterator(&src[i]);
          }
  
          /* Step 2: convert the dictionary into the final sorted set. */
          di = dictGetIterator(accumulator);
  
          /* We now are aware of the final size of the resulting sorted set,
           * let's resize the dictionary embedded inside the sorted set to the
           * right size, in order to save rehashing time. */
          dictExpand(dstzset->dict,dictSize(accumulator));
  
          while((de = dictNext(di)) != NULL) {
              sds ele = dictGetKey(de);
              score = dictGetDoubleVal(de);
              znode = zslInsert(dstzset->zsl,score,ele);
              dictAdd(dstzset->dict,ele,&znode->score);
          }
          dictReleaseIterator(di);
          dictRelease(accumulator);
      } else {
          serverPanic("Unknown operator");
      }
  
      if (dbDelete(c->db,dstkey))
          touched = 1;
      if (dstzset->zsl->length) {
          zsetConvertToZiplistIfNeeded(dstobj,maxelelen);
          dbAdd(c->db,dstkey,dstobj);
          addReplyLongLong(c,zsetLength(dstobj));
          signalModifiedKey(c,c->db,dstkey);
          notifyKeyspaceEvent(NOTIFY_ZSET,
              (op == SET_OP_UNION) ? "zunionstore" : "zinterstore",
              dstkey,c->db->id);
          server.dirty++;
      } else {
          decrRefCount(dstobj);
          addReply(c,shared.czero);
          if (touched) {
              signalModifiedKey(c,c->db,dstkey);
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",dstkey,c->db->id);
              server.dirty++;
          }
      }
      zfree(src);
  }
  
  void zunionstoreCommand(client *c) {
      zunionInterGenericCommand(c,c->argv[1], SET_OP_UNION);
  }
  
  void zinterstoreCommand(client *c) {
      zunionInterGenericCommand(c,c->argv[1], SET_OP_INTER);
  }
  
  void zrangeGenericCommand(client *c, int reverse) {
      robj *key = c->argv[1];
      robj *zobj;
      int withscores = 0;
      long start;
      long end;
      long llen;
      long rangelen;
  
      if ((getLongFromObjectOrReply(c, c->argv[2], &start, NULL) != C_OK) ||
          (getLongFromObjectOrReply(c, c->argv[3], &end, NULL) != C_OK)) return;
  
      if (c->argc == 5 && !strcasecmp(c->argv[4]->ptr,"withscores")) {
          withscores = 1;
      } else if (c->argc >= 5) {
          addReply(c,shared.syntaxerr);
          return;
      }
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.emptyarray)) == NULL
           || checkType(c,zobj,OBJ_ZSET)) return;
  
      /* Sanitize indexes. */
      llen = zsetLength(zobj);
      if (start < 0) start = llen+start;
      if (end < 0) end = llen+end;
      if (start < 0) start = 0;
  
      /* Invariant: start >= 0, so this test will be true when end < 0.
       * The range is empty when start > end or start >= length. */
      if (start > end || start >= llen) {
          addReply(c,shared.emptyarray);
          return;
      }
      if (end >= llen) end = llen-1;
      rangelen = (end-start)+1;
  
      /* Return the result in form of a multi-bulk reply. RESP3 clients
       * will receive sub arrays with score->element, while RESP2 returned
       * a flat array. */
      if (withscores && c->resp == 2)
          addReplyArrayLen(c, rangelen*2);
      else
          addReplyArrayLen(c, rangelen);
  
      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 (reverse)
              eptr = ziplistIndex(zl,-2-(2*start));
          else
              eptr = ziplistIndex(zl,2*start);
  
          serverAssertWithInfo(c,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
  
          while (rangelen--) {
              serverAssertWithInfo(c,zobj,eptr != NULL && sptr != NULL);
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
  
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              if (vstr == NULL)
                  addReplyBulkLongLong(c,vlong);
              else
                  addReplyBulkCBuffer(c,vstr,vlen);
              if (withscores) addReplyDouble(c,zzlGetScore(sptr));
  
              if (reverse)
                  zzlPrev(zl,&eptr,&sptr);
              else
                  zzlNext(zl,&eptr,&sptr);
          }
  
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *ln;
          sds ele;
  
          /* Check if starting point is trivial, before doing log(N) lookup. */
          if (reverse) {
              ln = zsl->tail;
              if (start > 0)
                  ln = zslGetElementByRank(zsl,llen-start);
          } else {
              ln = zsl->header->level[0].forward;
              if (start > 0)
                  ln = zslGetElementByRank(zsl,start+1);
          }
  
          while(rangelen--) {
              serverAssertWithInfo(c,zobj,ln != NULL);
              ele = ln->ele;
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              addReplyBulkCBuffer(c,ele,sdslen(ele));
              if (withscores) addReplyDouble(c,ln->score);
              ln = reverse ? ln->backward : ln->level[0].forward;
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  }
  
  void zrangeCommand(client *c) {
      zrangeGenericCommand(c,0);
  }
  
  void zrevrangeCommand(client *c) {
      zrangeGenericCommand(c,1);
  }
  
  /* This command implements ZRANGEBYSCORE, ZREVRANGEBYSCORE. */
  void genericZrangebyscoreCommand(client *c, int reverse) {
      zrangespec range;
      robj *key = c->argv[1];
      robj *zobj;
      long offset = 0, limit = -1;
      int withscores = 0;
      unsigned long rangelen = 0;
      void *replylen = NULL;
      int minidx, maxidx;
  
      /* Parse the range arguments. */
      if (reverse) {
          /* Range is given as [max,min] */
          maxidx = 2; minidx = 3;
      } else {
          /* Range is given as [min,max] */
          minidx = 2; maxidx = 3;
      }
  
      if (zslParseRange(c->argv[minidx],c->argv[maxidx],&range) != C_OK) {
          addReplyError(c,"min or max is not a float");
          return;
      }
  
      /* Parse optional extra arguments. Note that ZCOUNT will exactly have
       * 4 arguments, so we'll never enter the following code path. */
      if (c->argc > 4) {
          int remaining = c->argc - 4;
          int pos = 4;
  
          while (remaining) {
              if (remaining >= 1 && !strcasecmp(c->argv[pos]->ptr,"withscores")) {
                  pos++; remaining--;
                  withscores = 1;
              } else if (remaining >= 3 && !strcasecmp(c->argv[pos]->ptr,"limit")) {
                  if ((getLongFromObjectOrReply(c, c->argv[pos+1], &offset, NULL)
                          != C_OK) ||
                      (getLongFromObjectOrReply(c, c->argv[pos+2], &limit, NULL)
                          != C_OK))
                  {
                      return;
                  }
                  pos += 3; remaining -= 3;
              } else {
                  addReply(c,shared.syntaxerr);
                  return;
              }
          }
      }
  
      /* Ok, lookup the key and get the range */
      if ((zobj = lookupKeyReadOrReply(c,key,shared.emptyarray)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) 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;
          double score;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              eptr = zzlLastInRange(zl,&range);
          } else {
              eptr = zzlFirstInRange(zl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (eptr == NULL) {
              addReply(c,shared.emptyarray);
              return;
          }
  
          /* Get score pointer for the first element. */
          serverAssertWithInfo(c,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (eptr && offset--) {
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
  
          while (eptr && limit--) {
              score = zzlGetScore(sptr);
  
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zslValueGteMin(score,&range)) break;
              } else {
                  if (!zslValueLteMax(score,&range)) break;
              }
  
              /* We know the element exists, so ziplistGet should always
               * succeed */
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
  
              rangelen++;
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              if (vstr == NULL) {
                  addReplyBulkLongLong(c,vlong);
              } else {
                  addReplyBulkCBuffer(c,vstr,vlen);
              }
              if (withscores) addReplyDouble(c,score);
  
              /* Move to next node */
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *ln;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              ln = zslLastInRange(zsl,&range);
          } else {
              ln = zslFirstInRange(zsl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (ln == NULL) {
              addReply(c,shared.emptyarray);
              return;
          }
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (ln && offset--) {
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
  
          while (ln && limit--) {
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zslValueGteMin(ln->score,&range)) break;
              } else {
                  if (!zslValueLteMax(ln->score,&range)) break;
              }
  
              rangelen++;
              if (withscores && c->resp > 2) addReplyArrayLen(c,2);
              addReplyBulkCBuffer(c,ln->ele,sdslen(ln->ele));
              if (withscores) addReplyDouble(c,ln->score);
  
              /* Move to next node */
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      if (withscores && c->resp == 2) rangelen *= 2;
      setDeferredArrayLen(c, replylen, rangelen);
  }
  
  void zrangebyscoreCommand(client *c) {
      genericZrangebyscoreCommand(c,0);
  }
  
  void zrevrangebyscoreCommand(client *c) {
      genericZrangebyscoreCommand(c,1);
  }
  
  void zcountCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      zrangespec range;
      unsigned long count = 0;
  
      /* Parse the range arguments */
      if (zslParseRange(c->argv[2],c->argv[3],&range) != C_OK) {
          addReplyError(c,"min or max is not a float");
          return;
      }
  
      /* Lookup the sorted set */
      if ((zobj = lookupKeyReadOrReply(c, key, shared.czero)) == NULL ||
          checkType(c, zobj, OBJ_ZSET)) return;
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
          double score;
  
          /* Use the first element in range as the starting point */
          eptr = zzlFirstInRange(zl,&range);
  
          /* No "first" element */
          if (eptr == NULL) {
              addReply(c, shared.czero);
              return;
          }
  
          /* First element is in range */
          sptr = ziplistNext(zl,eptr);
          score = zzlGetScore(sptr);
          serverAssertWithInfo(c,zobj,zslValueLteMax(score,&range));
  
          /* Iterate over elements in range */
          while (eptr) {
              score = zzlGetScore(sptr);
  
              /* Abort when the node is no longer in range. */
              if (!zslValueLteMax(score,&range)) {
                  break;
              } else {
                  count++;
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *zn;
          unsigned long rank;
  
          /* Find first element in range */
          zn = zslFirstInRange(zsl, &range);
  
          /* Use rank of first element, if any, to determine preliminary count */
          if (zn != NULL) {
              rank = zslGetRank(zsl, zn->score, zn->ele);
              count = (zsl->length - (rank - 1));
  
              /* Find last element in range */
              zn = zslLastInRange(zsl, &range);
  
              /* Use rank of last element, if any, to determine the actual count */
              if (zn != NULL) {
                  rank = zslGetRank(zsl, zn->score, zn->ele);
                  count -= (zsl->length - rank);
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      addReplyLongLong(c, count);
  }
  
  void zlexcountCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      zlexrangespec range;
      unsigned long count = 0;
  
      /* Parse the range arguments */
      if (zslParseLexRange(c->argv[2],c->argv[3],&range) != C_OK) {
          addReplyError(c,"min or max not valid string range item");
          return;
      }
  
      /* Lookup the sorted set */
      if ((zobj = lookupKeyReadOrReply(c, key, shared.czero)) == NULL ||
          checkType(c, zobj, OBJ_ZSET))
      {
          zslFreeLexRange(&range);
          return;
      }
  
      if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
          unsigned char *zl = zobj->ptr;
          unsigned char *eptr, *sptr;
  
          /* Use the first element in range as the starting point */
          eptr = zzlFirstInLexRange(zl,&range);
  
          /* No "first" element */
          if (eptr == NULL) {
              zslFreeLexRange(&range);
              addReply(c, shared.czero);
              return;
          }
  
          /* First element is in range */
          sptr = ziplistNext(zl,eptr);
          serverAssertWithInfo(c,zobj,zzlLexValueLteMax(eptr,&range));
  
          /* Iterate over elements in range */
          while (eptr) {
              /* Abort when the node is no longer in range. */
              if (!zzlLexValueLteMax(eptr,&range)) {
                  break;
              } else {
                  count++;
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *zn;
          unsigned long rank;
  
          /* Find first element in range */
          zn = zslFirstInLexRange(zsl, &range);
  
          /* Use rank of first element, if any, to determine preliminary count */
          if (zn != NULL) {
              rank = zslGetRank(zsl, zn->score, zn->ele);
              count = (zsl->length - (rank - 1));
  
              /* Find last element in range */
              zn = zslLastInLexRange(zsl, &range);
  
              /* Use rank of last element, if any, to determine the actual count */
              if (zn != NULL) {
                  rank = zslGetRank(zsl, zn->score, zn->ele);
                  count -= (zsl->length - rank);
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      zslFreeLexRange(&range);
      addReplyLongLong(c, count);
  }
  
  /* This command implements ZRANGEBYLEX, ZREVRANGEBYLEX. */
  void genericZrangebylexCommand(client *c, int reverse) {
      zlexrangespec range;
      robj *key = c->argv[1];
      robj *zobj;
      long offset = 0, limit = -1;
      unsigned long rangelen = 0;
      void *replylen = NULL;
      int minidx, maxidx;
  
      /* Parse the range arguments. */
      if (reverse) {
          /* Range is given as [max,min] */
          maxidx = 2; minidx = 3;
      } else {
          /* Range is given as [min,max] */
          minidx = 2; maxidx = 3;
      }
  
      if (zslParseLexRange(c->argv[minidx],c->argv[maxidx],&range) != C_OK) {
          addReplyError(c,"min or max not valid string range item");
          return;
      }
  
      /* Parse optional extra arguments. Note that ZCOUNT will exactly have
       * 4 arguments, so we'll never enter the following code path. */
      if (c->argc > 4) {
          int remaining = c->argc - 4;
          int pos = 4;
  
          while (remaining) {
              if (remaining >= 3 && !strcasecmp(c->argv[pos]->ptr,"limit")) {
                  if ((getLongFromObjectOrReply(c, c->argv[pos+1], &offset, NULL) != C_OK) ||
                      (getLongFromObjectOrReply(c, c->argv[pos+2], &limit, NULL) != C_OK)) {
                      zslFreeLexRange(&range);
                      return;
                  }
                  pos += 3; remaining -= 3;
              } else {
                  zslFreeLexRange(&range);
                  addReply(c,shared.syntaxerr);
                  return;
              }
          }
      }
  
      /* Ok, lookup the key and get the range */
      if ((zobj = lookupKeyReadOrReply(c,key,shared.emptyarray)) == NULL ||
          checkType(c,zobj,OBJ_ZSET))
      {
          zslFreeLexRange(&range);
          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 reversed, get the last node in range as starting point. */
          if (reverse) {
              eptr = zzlLastInLexRange(zl,&range);
          } else {
              eptr = zzlFirstInLexRange(zl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (eptr == NULL) {
              addReply(c,shared.emptyarray);
              zslFreeLexRange(&range);
              return;
          }
  
          /* Get score pointer for the first element. */
          serverAssertWithInfo(c,zobj,eptr != NULL);
          sptr = ziplistNext(zl,eptr);
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (eptr && offset--) {
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
  
          while (eptr && limit--) {
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zzlLexValueGteMin(eptr,&range)) break;
              } else {
                  if (!zzlLexValueLteMax(eptr,&range)) break;
              }
  
              /* We know the element exists, so ziplistGet should always
               * succeed. */
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
  
              rangelen++;
              if (vstr == NULL) {
                  addReplyBulkLongLong(c,vlong);
              } else {
                  addReplyBulkCBuffer(c,vstr,vlen);
              }
  
              /* Move to next node */
              if (reverse) {
                  zzlPrev(zl,&eptr,&sptr);
              } else {
                  zzlNext(zl,&eptr,&sptr);
              }
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplist *zsl = zs->zsl;
          zskiplistNode *ln;
  
          /* If reversed, get the last node in range as starting point. */
          if (reverse) {
              ln = zslLastInLexRange(zsl,&range);
          } else {
              ln = zslFirstInLexRange(zsl,&range);
          }
  
          /* No "first" element in the specified interval. */
          if (ln == NULL) {
              addReply(c,shared.emptyarray);
              zslFreeLexRange(&range);
              return;
          }
  
          /* We don't know in advance how many matching elements there are in the
           * list, so we push this object that will represent the multi-bulk
           * length in the output buffer, and will "fix" it later */
          replylen = addReplyDeferredLen(c);
  
          /* If there is an offset, just traverse the number of elements without
           * checking the score because that is done in the next loop. */
          while (ln && offset--) {
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
  
          while (ln && limit--) {
              /* Abort when the node is no longer in range. */
              if (reverse) {
                  if (!zslLexValueGteMin(ln->ele,&range)) break;
              } else {
                  if (!zslLexValueLteMax(ln->ele,&range)) break;
              }
  
              rangelen++;
              addReplyBulkCBuffer(c,ln->ele,sdslen(ln->ele));
  
              /* Move to next node */
              if (reverse) {
                  ln = ln->backward;
              } else {
                  ln = ln->level[0].forward;
              }
          }
      } else {
          serverPanic("Unknown sorted set encoding");
      }
  
      zslFreeLexRange(&range);
      setDeferredArrayLen(c, replylen, rangelen);
  }
  
  void zrangebylexCommand(client *c) {
      genericZrangebylexCommand(c,0);
  }
  
  void zrevrangebylexCommand(client *c) {
      genericZrangebylexCommand(c,1);
  }
  
  void zcardCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.czero)) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      addReplyLongLong(c,zsetLength(zobj));
  }
  
  void zscoreCommand(client *c) {
      robj *key = c->argv[1];
      robj *zobj;
      double score;
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.null[c->resp])) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      if (zsetScore(zobj,c->argv[2]->ptr,&score) == C_ERR) {
          addReplyNull(c);
      } else {
          addReplyDouble(c,score);
      }
  }
  
  void zrankGenericCommand(client *c, int reverse) {
      robj *key = c->argv[1];
      robj *ele = c->argv[2];
      robj *zobj;
      long rank;
  
      if ((zobj = lookupKeyReadOrReply(c,key,shared.null[c->resp])) == NULL ||
          checkType(c,zobj,OBJ_ZSET)) return;
  
      serverAssertWithInfo(c,ele,sdsEncodedObject(ele));
      rank = zsetRank(zobj,ele->ptr,reverse);
      if (rank >= 0) {
          addReplyLongLong(c,rank);
      } else {
          addReplyNull(c);
      }
  }
  
  void zrankCommand(client *c) {
      zrankGenericCommand(c, 0);
  }
  
  void zrevrankCommand(client *c) {
      zrankGenericCommand(c, 1);
  }
  
  void zscanCommand(client *c) {
      robj *o;
      unsigned long cursor;
  
      if (parseScanCursorOrReply(c,c->argv[2],&cursor) == C_ERR) return;
      if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptyscan)) == NULL ||
          checkType(c,o,OBJ_ZSET)) return;
      scanGenericCommand(c,o,cursor);
  }
  
  /* This command implements the generic zpop operation, used by:
   * ZPOPMIN, ZPOPMAX, BZPOPMIN and BZPOPMAX. This function is also used
   * inside blocked.c in the unblocking stage of BZPOPMIN and BZPOPMAX.
   *
   * If 'emitkey' is true also the key name is emitted, useful for the blocking
   * behavior of BZPOP[MIN|MAX], since we can block into multiple keys.
   *
   * The synchronous version instead does not need to emit the key, but may
   * use the 'count' argument to return multiple items if available. */
  void genericZpopCommand(client *c, robj **keyv, int keyc, int where, int emitkey, robj *countarg) {
      int idx;
      robj *key = NULL;
      robj *zobj = NULL;
      sds ele;
      double score;
      long count = 1;
  
      /* If a count argument as passed, parse it or return an error. */
      if (countarg) {
          if (getLongFromObjectOrReply(c,countarg,&count,NULL) != C_OK)
              return;
          if (count <= 0) {
              addReply(c,shared.emptyarray);
              return;
          }
      }
  
      /* Check type and break on the first error, otherwise identify candidate. */
      idx = 0;
      while (idx < keyc) {
          key = keyv[idx++];
          zobj = lookupKeyWrite(c->db,key);
          if (!zobj) continue;
          if (checkType(c,zobj,OBJ_ZSET)) return;
          break;
      }
  
      /* No candidate for zpopping, return empty. */
      if (!zobj) {
          addReply(c,shared.emptyarray);
          return;
      }
  
      void *arraylen_ptr = addReplyDeferredLen(c);
      long arraylen = 0;
  
      /* We emit the key only for the blocking variant. */
      if (emitkey) addReplyBulk(c,key);
  
      /* Remove the element. */
      do {
          if (zobj->encoding == OBJ_ENCODING_ZIPLIST) {
              unsigned char *zl = zobj->ptr;
              unsigned char *eptr, *sptr;
              unsigned char *vstr;
              unsigned int vlen;
              long long vlong;
  
              /* Get the first or last element in the sorted set. */
              eptr = ziplistIndex(zl,where == ZSET_MAX ? -2 : 0);
              serverAssertWithInfo(c,zobj,eptr != NULL);
              serverAssertWithInfo(c,zobj,ziplistGet(eptr,&vstr,&vlen,&vlong));
              if (vstr == NULL)
                  ele = sdsfromlonglong(vlong);
              else
                  ele = sdsnewlen(vstr,vlen);
  
              /* Get the score. */
              sptr = ziplistNext(zl,eptr);
              serverAssertWithInfo(c,zobj,sptr != NULL);
              score = zzlGetScore(sptr);
          } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
              zset *zs = zobj->ptr;
              zskiplist *zsl = zs->zsl;
              zskiplistNode *zln;
  
              /* Get the first or last element in the sorted set. */
              zln = (where == ZSET_MAX ? zsl->tail :
                                         zsl->header->level[0].forward);
  
              /* There must be an element in the sorted set. */
              serverAssertWithInfo(c,zobj,zln != NULL);
              ele = sdsdup(zln->ele);
              score = zln->score;
          } else {
              serverPanic("Unknown sorted set encoding");
          }
  
          serverAssertWithInfo(c,zobj,zsetDel(zobj,ele));
          server.dirty++;
  
          if (arraylen == 0) { /* Do this only for the first iteration. */
              char *events[2] = {"zpopmin","zpopmax"};
              notifyKeyspaceEvent(NOTIFY_ZSET,events[where],key,c->db->id);
              signalModifiedKey(c,c->db,key);
          }
  
          addReplyBulkCBuffer(c,ele,sdslen(ele));
          addReplyDouble(c,score);
          sdsfree(ele);
          arraylen += 2;
  
          /* Remove the key, if indeed needed. */
          if (zsetLength(zobj) == 0) {
              dbDelete(c->db,key);
              notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
              break;
          }
      } while(--count);
  
      setDeferredArrayLen(c,arraylen_ptr,arraylen + (emitkey != 0));
  }
  
  /* ZPOPMIN key [<count>] */
  void zpopminCommand(client *c) {
      if (c->argc > 3) {
          addReply(c,shared.syntaxerr);
          return;
      }
      genericZpopCommand(c,&c->argv[1],1,ZSET_MIN,0,
          c->argc == 3 ? c->argv[2] : NULL);
  }
  
  /* ZMAXPOP key [<count>] */
  void zpopmaxCommand(client *c) {
      if (c->argc > 3) {
          addReply(c,shared.syntaxerr);
          return;
      }
      genericZpopCommand(c,&c->argv[1],1,ZSET_MAX,0,
          c->argc == 3 ? c->argv[2] : NULL);
  }
  
  /* BZPOPMIN / BZPOPMAX actual implementation. */
  void blockingGenericZpopCommand(client *c, int where) {
      robj *o;
      mstime_t timeout;
      int j;
  
      if (getTimeoutFromObjectOrReply(c,c->argv[c->argc-1],&timeout,UNIT_SECONDS)
          != C_OK) return;
  
      for (j = 1; j < c->argc-1; j++) {
          o = lookupKeyWrite(c->db,c->argv[j]);
          if (o != NULL) {
              if (o->type != OBJ_ZSET) {
                  addReply(c,shared.wrongtypeerr);
                  return;
              } else {
                  if (zsetLength(o) != 0) {
                      /* Non empty zset, this is like a normal ZPOP[MIN|MAX]. */
                      genericZpopCommand(c,&c->argv[j],1,where,1,NULL);
                      /* Replicate it as an ZPOP[MIN|MAX] instead of BZPOP[MIN|MAX]. */
                      rewriteClientCommandVector(c,2,
                          where == ZSET_MAX ? shared.zpopmax : shared.zpopmin,
                          c->argv[j]);
                      return;
                  }
              }
          }
      }
  
      /* If we are inside a MULTI/EXEC and the zset is empty the only thing
       * we can do is treating it as a timeout (even with timeout 0). */
      if (c->flags & CLIENT_MULTI) {
          addReplyNullArray(c);
          return;
      }
  
      /* If the keys do not exist we must block */
      blockForKeys(c,BLOCKED_ZSET,c->argv + 1,c->argc - 2,timeout,NULL,NULL);
  }
  
  // BZPOPMIN key [key ...] timeout
  void bzpopminCommand(client *c) {
      blockingGenericZpopCommand(c,ZSET_MIN);
  }
  
  // BZPOPMAX key [key ...] timeout
  void bzpopmaxCommand(client *c) {
      blockingGenericZpopCommand(c,ZSET_MAX);
  }
  