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https://github.com/fluencelabs/redis
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initial implementation for making the ziplist doubly linked
This commit is contained in:
Pieter Noordhuis
parent
fc2c0f7a6c
commit
dcb9cf4e82
159
ziplist.c
159
ziplist.c
@ -23,6 +23,11 @@
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#include "sds.h"
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#include "ziplist.h"
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/* Important note: the ZIP_END value is used to depict the end of the
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* ziplist structure. When a pointer contains an entry, the first couple
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* of bytes contain the encoded length of the previous entry. This length
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* is encoded as ZIP_ENC_RAW length, so the first two bits will contain 00
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* and the byte will therefore never have a value of 255. */
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#define ZIP_END 255
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#define ZIP_BIGLEN 254
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@ -40,8 +45,9 @@
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/* Utility macros */
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#define ZIPLIST_BYTES(zl) (*((unsigned int*)(zl)))
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#define ZIPLIST_LENGTH(zl) (*((zl)+sizeof(unsigned int)))
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#define ZIPLIST_HEADER_SIZE (sizeof(unsigned int)+1)
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#define ZIPLIST_TAIL_OFFSET(zl) (*((zl)+sizeof(unsigned int)))
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#define ZIPLIST_LENGTH(zl) (*((zl)+2*sizeof(unsigned int)))
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#define ZIPLIST_HEADER_SIZE (2*sizeof(unsigned int)+1)
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#define ZIPLIST_INCR_LENGTH(zl,incr) { \
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if (ZIPLIST_LENGTH(zl) < ZIP_BIGLEN) ZIPLIST_LENGTH(zl)+=incr; }
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@ -116,6 +122,14 @@ static unsigned int zipEncodeLength(unsigned char *p, char encoding, unsigned in
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return len;
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}
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/* Return the difference in number of bytes needed to store the new length
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* "len" on the entry pointed to by "p". */
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static int zipPrevLenByteDiff(unsigned char *p, unsigned int len) {
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unsigned int prevlensize;
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zipDecodeLength(p,&prevlensize);
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return zipEncodeLength(NULL,ZIP_ENC_RAW,len)-prevlensize;
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}
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/* Check if string pointed to by 'entry' can be encoded as an integer.
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* Stores the integer value in 'v' and its encoding in 'encoding'.
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* Warning: this function requires a NULL-terminated string! */
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@ -180,9 +194,12 @@ static long long zipLoadInteger(unsigned char *p, char encoding) {
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/* Return the total amount used by an entry (encoded length + payload). */
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static unsigned int zipRawEntryLength(unsigned char *p) {
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unsigned int lensize, len;
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len = zipDecodeLength(p, &lensize);
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return lensize + len;
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unsigned int prevlensize, lensize, len;
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/* Byte-size of encoded length of previous entry */
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zipDecodeLength(p,&prevlensize);
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/* Encoded length of this entry's payload */
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len = zipDecodeLength(p+prevlensize, &lensize);
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return prevlensize+lensize+len;
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}
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/* Create a new empty ziplist. */
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@ -190,6 +207,7 @@ unsigned char *ziplistNew(void) {
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unsigned int bytes = ZIPLIST_HEADER_SIZE+1;
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unsigned char *zl = zmalloc(bytes);
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ZIPLIST_BYTES(zl) = bytes;
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ZIPLIST_TAIL_OFFSET(zl) = ZIPLIST_HEADER_SIZE;
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ZIPLIST_LENGTH(zl) = 0;
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zl[bytes-1] = ZIP_END;
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return zl;
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@ -218,17 +236,30 @@ static unsigned char *ziplistTail(unsigned char *zl) {
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}
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unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int elen, int where) {
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unsigned int curlen = ZIPLIST_BYTES(zl), reqlen;
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unsigned char *p;
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unsigned int curlen = ZIPLIST_BYTES(zl), reqlen, prevlen;
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unsigned char *p, *curtail;
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char encoding = ZIP_ENC_RAW;
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long long value;
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/* We need to store the length of the current tail when the list
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* is non-empty and we push at the tail. */
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curtail = zl+ZIPLIST_TAIL_OFFSET(zl);
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if (where == ZIPLIST_TAIL && curtail[0] != ZIP_END) {
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prevlen = zipRawEntryLength(curtail);
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} else {
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prevlen = 0;
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}
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/* See if the entry can be encoded */
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if (zipTryEncoding(entry,&value,&encoding)) {
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reqlen = zipEncodingSize(encoding);
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} else {
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reqlen = elen;
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}
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/* We need space for both the length of the previous entry and
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* the length of the payload. */
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reqlen += zipEncodeLength(NULL,ZIP_ENC_RAW,prevlen);
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reqlen += zipEncodeLength(NULL,encoding,elen);
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/* Resize the ziplist and move if needed */
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@ -243,7 +274,17 @@ unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int
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p = zl+curlen-1;
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}
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/* Update tail offset if this is not the first element */
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if (curtail[0] != ZIP_END) {
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if (where == ZIPLIST_HEAD) {
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ZIPLIST_TAIL_OFFSET(zl) += reqlen;
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} else {
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ZIPLIST_TAIL_OFFSET(zl) += prevlen;
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}
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}
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/* Write the entry */
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p += zipEncodeLength(p,ZIP_ENC_RAW,prevlen);
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p += zipEncodeLength(p,encoding,elen);
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if (encoding != ZIP_ENC_RAW) {
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zipSaveInteger(p,value,encoding);
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@ -256,7 +297,9 @@ unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int
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unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
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unsigned int curlen = ZIPLIST_BYTES(zl), rawlen;
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unsigned int len, lensize;
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unsigned int prevrawlensize, prevrawlen, lensize, len, headerlen;
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int nextdiff = 0;
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unsigned char encoding;
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unsigned char *p;
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long long value;
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if (target) *target = NULL;
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@ -264,24 +307,46 @@ unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
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/* Get pointer to element to remove */
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p = (where == ZIPLIST_HEAD) ? ziplistHead(zl) : ziplistTail(zl);
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if (*p == ZIP_END) return zl;
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len = zipDecodeLength(p,&lensize);
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prevrawlen = zipDecodeLength(p,&prevrawlensize);
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len = zipDecodeLength(p+prevrawlensize,&lensize);
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headerlen = prevrawlensize+lensize;
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rawlen = headerlen+len;
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if (target) {
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if (ZIP_ENCODING(p) == ZIP_ENC_RAW) {
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*target = sdsnewlen(p+lensize,len);
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encoding = ZIP_ENCODING(p+prevrawlensize);
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if (encoding == ZIP_ENC_RAW) {
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*target = sdsnewlen(p+headerlen,len);
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} else {
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value = zipLoadInteger(p+lensize,ZIP_ENCODING(p));
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value = zipLoadInteger(p+headerlen,encoding);
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*target = sdscatprintf(sdsempty(), "%lld", value);
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}
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}
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/* Move list to front when popping from the head */
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rawlen = lensize+len;
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if (where == ZIPLIST_HEAD) {
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memmove(p,p+rawlen,curlen-ZIPLIST_HEADER_SIZE-len);
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/* The next entry will now be the head of the list */
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if (p[rawlen] != ZIP_END) {
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/* Tricky: storing the length of the previous entry in the next
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* entry (this previous length is always 0 when popping from the
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* head), might reduce the number of bytes needed.
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*
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* In this special case (new length is 0), we know that the
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* byte difference to store is always <= 0, which means that
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* we always have space to store it. */
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nextdiff = zipPrevLenByteDiff(p+rawlen,0);
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zipEncodeLength(p+rawlen-nextdiff,ZIP_ENC_RAW,0);
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}
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/* Move list to the front */
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memmove(p,p+rawlen-nextdiff,curlen-ZIPLIST_HEADER_SIZE-rawlen+nextdiff);
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/* Subtract the gained space from the tail offset */
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ZIPLIST_TAIL_OFFSET(zl) -= rawlen+nextdiff;
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} else {
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/* Subtract the length of the previous element from the tail offset. */
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ZIPLIST_TAIL_OFFSET(zl) -= prevrawlen;
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}
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/* Resize and update length */
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zl = ziplistResize(zl,curlen-rawlen);
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zl = ziplistResize(zl,curlen-rawlen+nextdiff);
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ZIPLIST_INCR_LENGTH(zl,-1);
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return zl;
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}
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@ -307,18 +372,21 @@ unsigned char *ziplistNext(unsigned char *p) {
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* to find out whether the string pointer or the integer value was set.
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* Return 0 if 'p' points to the end of the zipmap, 1 otherwise. */
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unsigned int ziplistGet(unsigned char *p, unsigned char **e, unsigned int *elen, long long *v) {
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unsigned int len, lensize;
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unsigned int prevrawlensize, lensize, len, headerlen;
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if (*p == ZIP_END) return 0;
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if (e) *e = NULL;
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len = zipDecodeLength(p,&lensize);
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if (ZIP_ENCODING(p) == ZIP_ENC_RAW) {
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zipDecodeLength(p,&prevrawlensize);
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len = zipDecodeLength(p+prevrawlensize,&lensize);
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headerlen = prevrawlensize+lensize;
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if (ZIP_ENCODING(p+prevrawlensize) == ZIP_ENC_RAW) {
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if (e) {
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*elen = len;
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*e = p+lensize;
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*e = p+headerlen;
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}
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} else {
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if (v) {
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*v = zipLoadInteger(p+lensize,ZIP_ENCODING(p));
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*v = zipLoadInteger(p+headerlen,ZIP_ENCODING(p+prevrawlensize));
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}
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}
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return 1;
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@ -368,24 +436,26 @@ unsigned char *ziplistDelete(unsigned char *zl, unsigned char **p) {
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/* Compare entry pointer to by 'p' with 'entry'. Return 1 if equal. */
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unsigned int ziplistCompare(unsigned char *p, unsigned char *entry, unsigned int elen) {
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unsigned int zlen, lensize;
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unsigned int prevrawlensize, lensize, len, headerlen;
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char encoding;
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long long zval, eval;
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long long val, eval;
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if (*p == ZIP_END) return 0;
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zlen = zipDecodeLength(p,&lensize);
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if (ZIP_ENCODING(p) == ZIP_ENC_RAW) {
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zipDecodeLength(p,&prevrawlensize);
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len = zipDecodeLength(p+prevrawlensize,&lensize);
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headerlen = prevrawlensize+lensize;
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if (ZIP_ENCODING(p+prevrawlensize) == ZIP_ENC_RAW) {
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/* Raw compare */
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if (zlen == elen) {
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return memcmp(p+lensize,entry,elen) == 0;
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if (len == elen) {
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return memcmp(p+headerlen,entry,elen) == 0;
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} else {
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return 0;
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}
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} else {
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if (zipTryEncoding(entry,&eval,&encoding)) {
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/* Do integer compare */
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zval = zipLoadInteger(p+lensize,ZIP_ENCODING(p));
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return zval == eval;
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val = zipLoadInteger(p+headerlen,ZIP_ENCODING(p+prevrawlensize));
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return val == eval;
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} else {
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/* Ziplist entry is integer encoded, but given entry is not. */
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}
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@ -418,22 +488,23 @@ unsigned int ziplistSize(unsigned char *zl) {
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void ziplistRepr(unsigned char *zl) {
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unsigned char *p, encoding;
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unsigned int l, lsize;
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unsigned int prevrawlensize, prevrawlen, lensize, len;
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printf("{total bytes %d} {length %u}\n",ZIPLIST_BYTES(zl), ZIPLIST_LENGTH(zl));
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p = ziplistHead(zl);
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while(*p != ZIP_END) {
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l = zipDecodeLength(p,&lsize);
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printf("{header %u, payload %u} ",lsize,l);
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encoding = ZIP_ENCODING(p);
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p += lsize;
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prevrawlen = zipDecodeLength(p,&prevrawlensize);
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len = zipDecodeLength(p+prevrawlensize,&lensize);
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printf("{offset %ld, header %u, payload %u} ",p-zl,prevrawlensize+lensize,len);
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encoding = ZIP_ENCODING(p+prevrawlensize);
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p += prevrawlensize+lensize;
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if (encoding == ZIP_ENC_RAW) {
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fwrite(p,l,1,stdout);
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fwrite(p,len,1,stdout);
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} else {
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printf("%lld", zipLoadInteger(p,encoding));
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}
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printf("\n");
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p += l;
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p += len;
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}
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printf("{end}\n\n");
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}
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@ -488,6 +559,14 @@ int main(int argc, char **argv) {
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printf("Pop head: %s (length %ld)\n", s, sdslen(s));
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ziplistRepr(zl);
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zl = ziplistPop(zl, &s, ZIPLIST_TAIL);
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printf("Pop tail: %s (length %ld)\n", s, sdslen(s));
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ziplistRepr(zl);
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zl = ziplistPop(zl, &s, ZIPLIST_TAIL);
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printf("Pop tail: %s (length %ld)\n", s, sdslen(s));
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ziplistRepr(zl);
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printf("Iterate list from 0 to end:\n");
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{
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zl = createList();
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@ -614,21 +693,21 @@ int main(int argc, char **argv) {
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zl = createList();
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p = ziplistIndex(zl, 0);
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if (!ziplistCompare(p,"hello",5)) {
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printf("ERROR\n");
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printf("ERROR: not \"hello\"\n");
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return;
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}
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if (ziplistCompare(p,"hella",5)) {
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printf("ERROR\n");
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printf("ERROR: \"hella\"\n");
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return;
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}
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p = ziplistIndex(zl, 3);
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if (!ziplistCompare(p,"1024",4)) {
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printf("ERROR\n");
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printf("ERROR: not \"1024\"\n");
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return;
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}
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if (ziplistCompare(p,"1025",4)) {
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printf("ERROR\n");
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printf("ERROR: \"1025\"\n");
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return;
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}
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printf("SUCCESS\n");
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