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. */
  
  /*
   * 用来实现有序集合相关的命令和接口
   * 其中hash table 保存redis object(实质就是sds)到score的映射，
   * skiplist保存score 到 redis object的映射，
   * 并且sds在hash table 和skiplist只保存一份，共用内存的，
   * 为了方便管理sds的内存，只在zslFreeNode接口中才可能释放sds对应的内存，
   * 相应的hash table是没有设置释放value的方法的,
   * 因此当从hash table中删除一个元素的时候，相应的也要从skiplist中删除
   */
  
  #include "server.h"
  #include <math.h>
  
  /*-----------------------------------------------------------------------------
   * Skiplist implementation of the low level API
   *----------------------------------------------------------------------------*/
  
   /*
    * skiplist 相关的接口的实现，都是以zsl作为前缀
    */
  
  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. */
  /* 创建指定层数skiplist的节点 */
  zskiplistNode *zslCreateNode(int level, double score, sds ele) {
      zskiplistNode *zn =
          zmalloc(sizeof(*zn)+level*sizeof(struct zskiplistLevel));
      zn->score = score;
      zn->ele = ele;
      return zn;
  }
  
  /* Create a new skiplist. */
  /* 创建一个新的skiplist */
  zskiplist *zslCreate(void) {
      int j;
      zskiplist *zsl;
  
      zsl = zmalloc(sizeof(*zsl));
      zsl->level = 1;
      zsl->length = 0;
      zsl->header = zslCreateNode(ZSKIPLIST_MAXLEVEL,0,NULL);
      for (j = 0; j < ZSKIPLIST_MAXLEVEL; j++) {
          zsl->header->level[j].forward = NULL;
          zsl->header->level[j].span = 0;
      }
      zsl->header->backward = NULL;
      zsl->tail = NULL;
      return zsl;
  }
  
  /* Free the specified skiplist node. The referenced SDS string representation
   * of the element is freed too, unless node->ele is set to NULL before calling
   * this function. */
  void zslFreeNode(zskiplistNode *node) {
      sdsfree(node->ele);
      zfree(node);
  }
  
  /* Free a whole skiplist. */
  /* 释放掉整个skiplist */
  void zslFree(zskiplist *zsl) {
      zskiplistNode *node = zsl->header->level[0].forward, *next;
  
      zfree(zsl->header);
  	/* 变量第一层链表上所有的元素 */
      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. */
  /*
   * 返回一个随机的层数，大小为[1, ZSKIPLIST_MAXLEVEL]，使用了power law分布，
   * 即越大的层数返回的概率越小
   */
  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'. */
  /*
   * 向skiplist中插入一个node
   */
  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;
      for (i = zsl->level-1; i >= 0; i--) {
          /* store rank that is crossed to reach the insert position */
          rank[i] = i == (zsl->level-1) ? 0 : rank[i+1];
          while (x->level[i].forward &&
                  (x->level[i].forward->score < score ||
                      (x->level[i].forward->score == score &&
                      sdscmp(x->level[i].forward->ele,ele) < 0)))
          {
              rank[i] += x->level[i].span;
              x = x->level[i].forward;
          }
          update[i] = x;
      }
      /* we assume the element is not already inside, since we allow duplicated
       * scores, reinserting the same element should never happen since the
       * caller of zslInsert() should test in the hash table if the element is
       * already inside or not. */
      level = zslRandomLevel();
      if (level > zsl->level) {
          for (i = zsl->level; i < level; i++) {
              rank[i] = 0;
              update[i] = zsl->header;
              update[i]->level[i].span = zsl->length;
          }
          zsl->level = level;
      }
      x = zslCreateNode(level,score,ele);
      for (i = 0; i < level; i++) {
          x->level[i].forward = update[i]->level[i].forward;
          update[i]->level[i].forward = x;
  
          /* update span covered by update[i] as x is inserted here */
          x->level[i].span = update[i]->level[i].span - (rank[0] - rank[i]);
          update[i]->level[i].span = (rank[0] - rank[i]) + 1;
      }
  
      /* increment span for untouched levels */
      for (i = level; i < zsl->level; i++) {
          update[i]->level[i].span++;
      }
  
      x->backward = (update[0] == zsl->header) ? NULL : update[0];
      if (x->level[0].forward)
          x->level[0].forward->backward = x;
      else
          zsl->tail = x;
      zsl->length++;
      return x;
  }
  
  /* Internal function used by zslDelete, zslDeleteByScore and zslDeleteByRank */
  void zslDeleteNode(zskiplist *zsl, zskiplistNode *x, zskiplistNode **update) {
      int i;
      for (i = 0; i < zsl->level; i++) {
          if (update[i]->level[i].forward == x) {
              update[i]->level[i].span += x->level[i].span - 1;
              update[i]->level[i].forward = x->level[i].forward;
          } else {
              update[i]->level[i].span -= 1;
          }
      }
      if (x->level[0].forward) {
          x->level[0].forward->backward = x->backward;
      } else {
          zsl->tail = x->backward;
      }
      while(zsl->level > 1 && zsl->header->level[zsl->level-1].forward == NULL)
          zsl->level--;
      zsl->length--;
  }
  
  /* Delete an element with matching score/element from the skiplist.
   * The function returns 1 if the node was found and deleted, otherwise
   * 0 is returned.
   *
   * If 'node' is NULL the deleted node is freed by zslFreeNode(), otherwise
   * it is not freed (but just unlinked) and *node is set to the node pointer,
   * so that it is possible for the caller to reuse the node (including the
   * referenced SDS string at node->ele). */
  int zslDelete(zskiplist *zsl, double score, sds ele, zskiplistNode **node) {
      zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
      int i;
  
      x = zsl->header;
      for (i = zsl->level-1; i >= 0; i--) {
          while (x->level[i].forward &&
                  (x->level[i].forward->score < score ||
                      (x->level[i].forward->score == score &&
                       sdscmp(x->level[i].forward->ele,ele) < 0)))
          {
              x = x->level[i].forward;
          }
          update[i] = x;
      }
      /* We may have multiple elements with the same score, what we need
       * is to find the element with both the right score and object. */
      x = x->level[0].forward;
      if (x && score == x->score && sdscmp(x->ele,ele) == 0) {
          zslDeleteNode(zsl, x, update);
          if (!node)
              zslFreeNode(x);
          else
              *node = x;
          return 1;
      }
      return 0; /* not found */
  }
  
  /* 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
   *----------------------------------------------------------------------------*/
   
   /*
    * 用ziplist实现有序集合相关的接口，接口都是以zzl作为前缀的
    */
  
  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;
  }
  
  /* 
   * 转换集合的实现方式，比如用ziplist 转换为 hashtable+skiplist 
   * 参数encoding 是目标编码方式
   * */
  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);
  
  		/* 把ziplist中所有的元素插入的skiplist中 */
          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. */
  
  		/* 释放原来的skiplist，同时把相应的元素保存到ziplist中 */
          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 erorr, currently only when the increment
   * produces a NAN condition, or when the 'score' value is NAN since the
   * start.
   *
   * The commad as a side effect of adding a new element may convert the sorted
   * set internal encoding from ziplist to hashtable+skiplist.
   *
   * Memory managemnet of 'ele':
   *
   * The function does not take ownership of the 'ele' SDS string, but copies
   * it if needed. */
  
  /*
   * 向集合中增加或更新一个元素的通用接口，不管底层是用ziplist，还是skiplist实现，
   * 参数flags作为输入值，执行不同的操作，同时用来保存返回值
   * 参数newscore用在ZADD_INCR命令中，保存最新的score
   *
   * 这个接口可能触发把集合的实现由ziplist 改成 hashtable + skiplist
   */
  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);
  			/* 检测是否需要转换集合的实现方式为hashtable + skiplist */
              if (zzlLength(zobj->ptr) > server.zset_max_ziplist_entries ||
                  sdslen(ele) > server.zset_max_ziplist_value)
                  zsetConvert(zobj,OBJ_ENCODING_SKIPLIST);
              if (newscore) *newscore = score;
              *flags |= ZADD_ADDED;
              return 1;
          } else {
              *flags |= ZADD_NOP;
              return 1;
          }
      } else if (zobj->encoding == OBJ_ENCODING_SKIPLIST) {
          zset *zs = zobj->ptr;
          zskiplistNode *znode;
          dictEntry *de;
  
          de = dictFind(zs->dict,ele);
          if (de != NULL) {
              /* NX? Return, same element already exists. */
              if (nx) {
                  *flags |= ZADD_NOP;
                  return 1;
              }
              curscore = *(double*)dictGetVal(de);
  
              /* Prepare the score for the increment if needed. */
              if (incr) {
                  score += curscore;
                  if (isnan(score)) {
                      *flags |= ZADD_NAN;
                      return 0;
                  }
                  if (newscore) *newscore = score;
              }
  
              /* Remove and re-insert when score changes. */
              if (score != curscore) {
  				/* 更新skiplist 和 dict */
                  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) {
  			/* 同时向skiplist 和 dict 插入，并且ele在skiplist和dict只保存一份 */
              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. */
  /* 用来实现 ZADD 和 ZINCRBY 命令*/
  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. */
  		/* 根据不同的情况使用不同的数据结构 */
          if (server.zset_max_ziplist_entries == 0 ||
              server.zset_max_ziplist_value < sdslen(c->argv[scoreidx+1]->ptr))
          {
  			/* 使用skiplist实现 */
              zobj = createZsetObject();
          } else {
  			/* 使用ziplist实现 */
              zobj = createZsetZiplistObject();
          }
          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->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->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->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->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->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->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);
  }
  