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use less memory as element->span[0] will always be 1; any level 0 skip list is essentially a linked list

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Pieter Noordhuis 2010-03-03 19:04:38 +01:00
parent 912b9165a9
commit 2b37892e9b
1 changed files with 34 additions and 15 deletions
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49
redis.c
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@ -4798,7 +4798,8 @@ static zskiplistNode *zslCreateNode(int level, double score, robj *obj) {
zskiplistNode *zn = zmalloc(sizeof(*zn));
zn->forward = zmalloc(sizeof(zskiplistNode*) * level);
zn->span = zmalloc(sizeof(unsigned int) * level);
if (level > 0)
zn->span = zmalloc(sizeof(unsigned int) * (level - 1));
zn->score = score;
zn->obj = obj;
return zn;
@ -4851,19 +4852,23 @@ static int zslRandomLevel(void) {
static void zslInsert(zskiplist *zsl, double score, robj *obj) {
zskiplistNode *update[ZSKIPLIST_MAXLEVEL], *x;
unsigned int span[ZSKIPLIST_MAXLEVEL];
unsigned int rank[ZSKIPLIST_MAXLEVEL];
int i, level;
x = zsl->header;
for (i = zsl->level-1; i >= 0; i--) {
/* store span that is crossed to reach the insert position */
span[i] = i == (zsl->level-1) ? 0 : span[i+1];
/* store rank that is crossed to reach the insert position */
rank[i] = i == (zsl->level-1) ? 0 : rank[i+1];
while (x->forward[i] &&
(x->forward[i]->score < score ||
(x->forward[i]->score == score &&
compareStringObjects(x->forward[i]->obj,obj) < 0))) {
span[i] += x->span[i];
if (i > 0) {
rank[i] += x->span[i-1];
} else {
rank[i]++;
}
x = x->forward[i];
}
update[i] = x;
@ -4875,9 +4880,9 @@ static void zslInsert(zskiplist *zsl, double score, robj *obj) {
level = zslRandomLevel();
if (level > zsl->level) {
for (i = zsl->level; i < level; i++) {
span[i] = 0;
rank[i] = 0;
update[i] = zsl->header;
update[i]->span[i] = zsl->length;
update[i]->span[i-1] = zsl->length;
}
zsl->level = level;
}
@ -4887,13 +4892,15 @@ static void zslInsert(zskiplist *zsl, double score, robj *obj) {
update[i]->forward[i] = x;
/* update span covered by update[i] as x is inserted here */
x->span[i] = update[i]->span[i] - (span[0] - span[i]);
update[i]->span[i] = (span[0] - span[i]) + 1;
if (i > 0) {
x->span[i-1] = update[i]->span[i-1] - (rank[0] - rank[i]);
update[i]->span[i-1] = (rank[0] - rank[i]) + 1;
}
}
/* increment span for untouched levels */
for (i = level; i < zsl->level; i++) {
update[i]->span[i]++;
update[i]->span[i-1]++;
}
x->backward = (update[0] == zsl->header) ? NULL : update[0];
@ -4924,10 +4931,14 @@ static int zslDelete(zskiplist *zsl, double score, robj *obj) {
if (x && score == x->score && compareStringObjects(x->obj,obj) == 0) {
for (i = 0; i < zsl->level; i++) {
if (update[i]->forward[i] == x) {
update[i]->span[i] += x->span[i] - 1;
if (i > 0) {
update[i]->span[i-1] += x->span[i-1] - 1;
}
update[i]->forward[i] = x->forward[i];
} else {
update[i]->span[i] -= 1;
/* invariant: i > 0, because update[0]->forward[0]
* is always equal to x */
update[i]->span[i-1] -= 1;
}
}
if (x->forward[0]) {
@ -4969,10 +4980,14 @@ static unsigned long zslDeleteRange(zskiplist *zsl, double min, double max, dict
for (i = 0; i < zsl->level; i++) {
if (update[i]->forward[i] == x) {
update[i]->span[i] += x->span[i] - 1;
if (i > 0) {
update[i]->span[i-1] += x->span[i-1] - 1;
}
update[i]->forward[i] = x->forward[i];
} else {
update[i]->span[i] -= 1;
/* invariant: i > 0, because update[0]->forward[0]
* is always equal to x */
update[i]->span[i-1] -= 1;
}
}
if (x->forward[0]) {
@ -5443,7 +5458,11 @@ static void zrankCommand(redisClient *c) {
(x->forward[i]->score < *score ||
(x->forward[i]->score == *score &&
compareStringObjects(x->forward[i]->obj,c->argv[2]) < 0))) {
rank += x->span[i];
if (i > 0) {
rank += x->span[i-1];
} else {
rank++;
}
x = x->forward[i];
}