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function to insert an element at an arbitrary position in the list

This commit is contained in:
Pieter Noordhuis 2010-05-29 18:52:49 +02:00
parent 0c0d056412
commit 6435c76772
1 changed files with 45 additions and 32 deletions
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77
ziplist.c
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@ -286,66 +286,79 @@ static unsigned char *__ziplistDelete(unsigned char *zl, unsigned char *p, int n
return zl;
}
unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int elen, int where) {
unsigned int curlen = ZIPLIST_BYTES(zl), reqlen, prevlen;
unsigned char *p, *curtail;
/* Insert item at "p". */
static unsigned char *__ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
unsigned int curlen = ZIPLIST_BYTES(zl), reqlen, prevlen = 0;
unsigned int offset, nextdiff = 0;
unsigned char *tail;
char encoding = ZIP_ENC_RAW;
long long value;
zlentry entry;
/* We need to store the length of the current tail when the list
* is non-empty and we push at the tail. */
curtail = zl+ZIPLIST_TAIL_OFFSET(zl);
if (where == ZIPLIST_TAIL && curtail[0] != ZIP_END) {
prevlen = zipRawEntryLength(curtail);
/* Find out prevlen for the entry that is inserted. */
if (p[0] != ZIP_END) {
entry = zipEntry(p);
prevlen = entry.prevrawlen;
} else {
prevlen = 0;
tail = ziplistTail(zl);
if (tail[0] != ZIP_END) {
prevlen = zipRawEntryLength(tail);
}
}
/* See if the entry can be encoded */
if (zipTryEncoding(entry,&value,&encoding)) {
if (zipTryEncoding(s,&value,&encoding)) {
reqlen = zipEncodingSize(encoding);
} else {
reqlen = elen;
reqlen = slen;
}
/* We need space for both the length of the previous entry and
* the length of the payload. */
reqlen += zipEncodeLength(NULL,ZIP_ENC_RAW,prevlen);
reqlen += zipEncodeLength(NULL,encoding,elen);
reqlen += zipEncodeLength(NULL,encoding,slen);
/* Resize the ziplist and move if needed */
zl = ziplistResize(zl,curlen+reqlen);
if (where == ZIPLIST_HEAD) {
p = zl+ZIPLIST_HEADER_SIZE;
if (*p != ZIP_END) {
/* Subtract one because of the ZIP_END bytes */
memmove(p+reqlen,p,curlen-ZIPLIST_HEADER_SIZE-1);
}
/* When the insert position is not equal to the tail, we need to
* make sure that the next entry can hold this entry's length in
* its prevlen field. */
nextdiff = p[0] != ZIP_END ? zipPrevLenByteDiff(p,reqlen) : 0;
/* Store offset because a realloc may change the address of zl. */
offset = p-zl;
zl = ziplistResize(zl,curlen+reqlen+nextdiff);
p = zl+offset;
/* Apply memory move when necessary and update tail offset. */
if (p[0] != ZIP_END) {
/* Subtract one because of the ZIP_END bytes */
memmove(p+reqlen,p-nextdiff,curlen-offset-1+nextdiff);
/* Encode this entry's raw length in the next entry. */
zipEncodeLength(p+reqlen,ZIP_ENC_RAW,reqlen);
/* Update offset for tail */
ZIPLIST_TAIL_OFFSET(zl) += reqlen+nextdiff;
} else {
p = zl+curlen-1;
}
/* Update tail offset if this is not the first element */
if (curtail[0] != ZIP_END) {
if (where == ZIPLIST_HEAD) {
ZIPLIST_TAIL_OFFSET(zl) += reqlen;
} else {
ZIPLIST_TAIL_OFFSET(zl) += prevlen;
}
/* This element will be the new tail. */
ZIPLIST_TAIL_OFFSET(zl) = p-zl;
}
/* Write the entry */
p += zipEncodeLength(p,ZIP_ENC_RAW,prevlen);
p += zipEncodeLength(p,encoding,elen);
p += zipEncodeLength(p,encoding,slen);
if (encoding != ZIP_ENC_RAW) {
zipSaveInteger(p,value,encoding);
} else {
memcpy(p,entry,elen);
memcpy(p,s,slen);
}
ZIPLIST_INCR_LENGTH(zl,1);
return zl;
}
unsigned char *ziplistPush(unsigned char *zl, unsigned char *s, unsigned int slen, int where) {
unsigned char *p;
p = (where == ZIPLIST_HEAD) ? ziplistHead(zl) : (zl+ZIPLIST_BYTES(zl)-1);
return __ziplistInsert(zl,p,s,slen);
}
unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
zlentry entry;
unsigned char *p;