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use rank to find starting point for ZRANGE and ZREVRANGE

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This commit is contained in:
Pieter Noordhuis 2010-03-04 14:16:07 +01:00
parent 27b0ccca71
commit e74825c24f
1 changed files with 22 additions and 6 deletions
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28
redis.c
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@ -5081,6 +5081,26 @@ static unsigned long zslGetRank(zskiplist *zsl, double score, robj *o) {
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->forward[i] && (traversed + x->span[i]) <= rank) {
traversed += x->span[i];
x = x->forward[i];
}
if (traversed == rank) {
return x;
}
}
return NULL;
}
/* The actual Z-commands implementations */
/* This generic command implements both ZADD and ZINCRBY.
@ -5282,13 +5302,9 @@ static void zrangeGenericCommand(redisClient *c, int reverse) {
/* Return the result in form of a multi-bulk reply */
if (reverse) {
ln = zsl->tail;
while (start--)
ln = ln->backward;
ln = zslGetElementByRank(zsl, llen - start);
} else {
ln = zsl->header->forward[0];
while (start--)
ln = ln->forward[0];
ln = zslGetElementByRank(zsl, start + 1);
}
addReplySds(c,sdscatprintf(sdsempty(),"*%d\r\n",