From: Pieter Noordhuis Date: Sat, 29 May 2010 15:38:23 +0000 (+0200) Subject: extract a generic delete function that can be used in pop and delete(range) X-Git-Url: https://git.saurik.com/redis.git/commitdiff_plain/0c0d0564121eb758fa25e2edf43cb1cf42aadbbc?ds=sidebyside extract a generic delete function that can be used in pop and delete(range) --- diff --git a/ziplist.c b/ziplist.c index 16e9dbc1..57639c3a 100644 --- a/ziplist.c +++ b/ziplist.c @@ -56,6 +56,7 @@ typedef struct zlentry { unsigned int lensize, len; unsigned int headersize; unsigned char encoding; + unsigned char *p; } zlentry; /* Return bytes needed to store integer encoded by 'encoding' */ @@ -206,6 +207,7 @@ static zlentry zipEntry(unsigned char *p) { e.len = zipDecodeLength(p+e.prevrawlensize,&e.lensize); e.headersize = e.prevrawlensize+e.lensize; e.encoding = ZIP_ENCODING(p+e.prevrawlensize); + e.p = p; return e; } @@ -246,6 +248,42 @@ static unsigned char *ziplistTail(unsigned char *zl) { p += zipRawEntryLength(p); } return q; + +/* Delete "num" entries, starting at "p". Returns pointer to the ziplist. */ +static unsigned char *__ziplistDelete(unsigned char *zl, unsigned char *p, int num) { + unsigned int i, totlen, deleted = 0; + int nextdiff = 0; + zlentry first = zipEntry(p); + for (i = 0; p[0] != ZIP_END && i < num; i++) { + p += zipRawEntryLength(p); + deleted++; + } + + totlen = p-first.p; + if (totlen > 0) { + if (p[0] != ZIP_END) { + /* Tricky: storing the prevlen in this entry might reduce or + * increase the number of bytes needed, compared to the current + * prevlen. Note that we can always store this length because + * it was previously stored by an entry that is being deleted. */ + nextdiff = zipPrevLenByteDiff(p,first.prevrawlen); + zipEncodeLength(p-nextdiff,ZIP_ENC_RAW,first.prevrawlen); + + /* Update offset for tail */ + ZIPLIST_TAIL_OFFSET(zl) -= totlen+nextdiff; + + /* Move tail to the front of the ziplist */ + memmove(first.p,p-nextdiff,ZIPLIST_BYTES(zl)-(p-zl)-1+nextdiff); + } else { + /* The entire tail was deleted. No need to move memory. */ + ZIPLIST_TAIL_OFFSET(zl) = (first.p-zl)-first.prevrawlen; + } + + /* Resize and update length */ + zl = ziplistResize(zl, ZIPLIST_BYTES(zl)-totlen+nextdiff); + ZIPLIST_INCR_LENGTH(zl,-deleted); + } + return zl; } unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int elen, int where) { @@ -309,9 +347,7 @@ unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int } unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) { - unsigned int curlen = ZIPLIST_BYTES(zl), rawlen; zlentry entry; - int nextdiff = 0; unsigned char *p; long long value; if (target) *target = NULL; @@ -321,7 +357,6 @@ unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) { if (*p == ZIP_END) return zl; entry = zipEntry(p); - rawlen = entry.headersize+entry.len; if (target) { if (entry.encoding == ZIP_ENC_RAW) { *target = sdsnewlen(p+entry.headersize,entry.len); @@ -331,32 +366,7 @@ unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) { } } - if (where == ZIPLIST_HEAD) { - /* The next entry will now be the head of the list */ - if (p[rawlen] != ZIP_END) { - /* Tricky: storing the length of the previous entry in the next - * entry (this previous length is always 0 when popping from the - * head), might reduce the number of bytes needed. - * - * In this special case (new length is 0), we know that the - * byte difference to store is always <= 0, which means that - * we always have space to store it. */ - nextdiff = zipPrevLenByteDiff(p+rawlen,0); - zipEncodeLength(p+rawlen-nextdiff,ZIP_ENC_RAW,0); - } - /* Move list to the front */ - memmove(p,p+rawlen-nextdiff,curlen-ZIPLIST_HEADER_SIZE-rawlen+nextdiff); - - /* Subtract the gained space from the tail offset */ - ZIPLIST_TAIL_OFFSET(zl) -= rawlen+nextdiff; - } else { - /* Subtract the length of the previous element from the tail offset. */ - ZIPLIST_TAIL_OFFSET(zl) -= entry.prevrawlen; - } - - /* Resize and update length */ - zl = ziplistResize(zl,curlen-rawlen+nextdiff); - ZIPLIST_INCR_LENGTH(zl,-1); + zl = __ziplistDelete(zl,p,1); return zl; } @@ -401,42 +411,19 @@ unsigned int ziplistGet(unsigned char *p, unsigned char **sstr, unsigned int *sl /* Delete a range of entries from the ziplist. */ unsigned char *ziplistDeleteRange(unsigned char *zl, unsigned int index, unsigned int num) { - unsigned char *p, *first = ziplistIndex(zl, index); - unsigned int i, totlen, deleted = 0; - for (p = first, i = 0; *p != ZIP_END && i < num; i++) { - p += zipRawEntryLength(p); - deleted++; - } - - totlen = p-first; - if (totlen > 0) { - /* Move current tail to the new tail when there *is* a tail */ - if (*p != ZIP_END) memmove(first,p,ZIPLIST_BYTES(zl)-(p-zl)-1); - - /* Resize and update length */ - zl = ziplistResize(zl, ZIPLIST_BYTES(zl)-totlen); - ZIPLIST_INCR_LENGTH(zl,-deleted); - } - return zl; + unsigned char *p = ziplistIndex(zl,index); + return __ziplistDelete(zl,p,num); } /* Delete a single entry from the ziplist, pointed to by *p. * Also update *p in place, to be able to iterate over the * ziplist, while deleting entries. */ unsigned char *ziplistDelete(unsigned char *zl, unsigned char **p) { - unsigned int offset = *p-zl, tail, len; - len = zipRawEntryLength(*p); - tail = ZIPLIST_BYTES(zl)-offset-len-1; - - /* Move current tail to the new tail when there *is* a tail */ - if (tail > 0) memmove(*p,*p+len,tail); - - /* Resize and update length */ - zl = ziplistResize(zl, ZIPLIST_BYTES(zl)-len); - ZIPLIST_INCR_LENGTH(zl,-1); + unsigned int offset = *p-zl; + zl = __ziplistDelete(zl,*p,1); - /* Store new pointer to current element in p. - * This needs to be done because zl can change on realloc. */ + /* Store pointer to current element in p, because ziplistDelete will + * do a realloc which might result in a different "zl"-pointer. */ *p = zl+offset; return zl; }