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initial implementation for making the ziplist doubly linked

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This commit is contained in:
Pieter Noordhuis 2010-05-29 15:40:40 +02:00
parent fc2c0f7a6c
commit dcb9cf4e82
1 changed files with 119 additions and 40 deletions
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159
ziplist.c
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@ -23,6 +23,11 @@
#include "sds.h" #include "sds.h"
#include "ziplist.h" #include "ziplist.h"
/* Important note: the ZIP_END value is used to depict the end of the
* ziplist structure. When a pointer contains an entry, the first couple
* of bytes contain the encoded length of the previous entry. This length
* is encoded as ZIP_ENC_RAW length, so the first two bits will contain 00
* and the byte will therefore never have a value of 255. */
#define ZIP_END 255 #define ZIP_END 255
#define ZIP_BIGLEN 254 #define ZIP_BIGLEN 254
@ -40,8 +45,9 @@
/* Utility macros */ /* Utility macros */
#define ZIPLIST_BYTES(zl) (*((unsigned int*)(zl))) #define ZIPLIST_BYTES(zl) (*((unsigned int*)(zl)))
#define ZIPLIST_LENGTH(zl) (*((zl)+sizeof(unsigned int))) #define ZIPLIST_TAIL_OFFSET(zl) (*((zl)+sizeof(unsigned int)))
#define ZIPLIST_HEADER_SIZE (sizeof(unsigned int)+1) #define ZIPLIST_LENGTH(zl) (*((zl)+2*sizeof(unsigned int)))
#define ZIPLIST_HEADER_SIZE (2*sizeof(unsigned int)+1)
#define ZIPLIST_INCR_LENGTH(zl,incr) { \ #define ZIPLIST_INCR_LENGTH(zl,incr) { \
if (ZIPLIST_LENGTH(zl) < ZIP_BIGLEN) ZIPLIST_LENGTH(zl)+=incr; } if (ZIPLIST_LENGTH(zl) < ZIP_BIGLEN) ZIPLIST_LENGTH(zl)+=incr; }
@ -116,6 +122,14 @@ static unsigned int zipEncodeLength(unsigned char *p, char encoding, unsigned in
return len; return len;
} }
/* Return the difference in number of bytes needed to store the new length
* "len" on the entry pointed to by "p". */
static int zipPrevLenByteDiff(unsigned char *p, unsigned int len) {
unsigned int prevlensize;
zipDecodeLength(p,&prevlensize);
return zipEncodeLength(NULL,ZIP_ENC_RAW,len)-prevlensize;
}
/* Check if string pointed to by 'entry' can be encoded as an integer. /* Check if string pointed to by 'entry' can be encoded as an integer.
* Stores the integer value in 'v' and its encoding in 'encoding'. * Stores the integer value in 'v' and its encoding in 'encoding'.
* Warning: this function requires a NULL-terminated string! */ * Warning: this function requires a NULL-terminated string! */
@ -180,9 +194,12 @@ static long long zipLoadInteger(unsigned char *p, char encoding) {
/* Return the total amount used by an entry (encoded length + payload). */ /* Return the total amount used by an entry (encoded length + payload). */
static unsigned int zipRawEntryLength(unsigned char *p) { static unsigned int zipRawEntryLength(unsigned char *p) {
unsigned int lensize, len; unsigned int prevlensize, lensize, len;
len = zipDecodeLength(p, &lensize); /* Byte-size of encoded length of previous entry */
return lensize + len; zipDecodeLength(p,&prevlensize);
/* Encoded length of this entry's payload */
len = zipDecodeLength(p+prevlensize, &lensize);
return prevlensize+lensize+len;
} }
/* Create a new empty ziplist. */ /* Create a new empty ziplist. */
@ -190,6 +207,7 @@ unsigned char *ziplistNew(void) {
unsigned int bytes = ZIPLIST_HEADER_SIZE+1; unsigned int bytes = ZIPLIST_HEADER_SIZE+1;
unsigned char *zl = zmalloc(bytes); unsigned char *zl = zmalloc(bytes);
ZIPLIST_BYTES(zl) = bytes; ZIPLIST_BYTES(zl) = bytes;
ZIPLIST_TAIL_OFFSET(zl) = ZIPLIST_HEADER_SIZE;
ZIPLIST_LENGTH(zl) = 0; ZIPLIST_LENGTH(zl) = 0;
zl[bytes-1] = ZIP_END; zl[bytes-1] = ZIP_END;
return zl; return zl;
@ -218,17 +236,30 @@ static unsigned char *ziplistTail(unsigned char *zl) {
} }
unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int elen, int where) { unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int elen, int where) {
unsigned int curlen = ZIPLIST_BYTES(zl), reqlen; unsigned int curlen = ZIPLIST_BYTES(zl), reqlen, prevlen;
unsigned char *p; unsigned char *p, *curtail;
char encoding = ZIP_ENC_RAW; char encoding = ZIP_ENC_RAW;
long long value; long long value;
/* 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);
} else {
prevlen = 0;
}
/* See if the entry can be encoded */ /* See if the entry can be encoded */
if (zipTryEncoding(entry,&value,&encoding)) { if (zipTryEncoding(entry,&value,&encoding)) {
reqlen = zipEncodingSize(encoding); reqlen = zipEncodingSize(encoding);
} else { } else {
reqlen = elen; reqlen = elen;
} }
/* 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,elen);
/* Resize the ziplist and move if needed */ /* Resize the ziplist and move if needed */
@ -243,7 +274,17 @@ unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int
p = zl+curlen-1; 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;
}
}
/* Write the entry */ /* Write the entry */
p += zipEncodeLength(p,ZIP_ENC_RAW,prevlen);
p += zipEncodeLength(p,encoding,elen); p += zipEncodeLength(p,encoding,elen);
if (encoding != ZIP_ENC_RAW) { if (encoding != ZIP_ENC_RAW) {
zipSaveInteger(p,value,encoding); zipSaveInteger(p,value,encoding);
@ -256,7 +297,9 @@ unsigned char *ziplistPush(unsigned char *zl, unsigned char *entry, unsigned int
unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) { unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
unsigned int curlen = ZIPLIST_BYTES(zl), rawlen; unsigned int curlen = ZIPLIST_BYTES(zl), rawlen;
unsigned int len, lensize; unsigned int prevrawlensize, prevrawlen, lensize, len, headerlen;
int nextdiff = 0;
unsigned char encoding;
unsigned char *p; unsigned char *p;
long long value; long long value;
if (target) *target = NULL; if (target) *target = NULL;
@ -264,24 +307,46 @@ unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
/* Get pointer to element to remove */ /* Get pointer to element to remove */
p = (where == ZIPLIST_HEAD) ? ziplistHead(zl) : ziplistTail(zl); p = (where == ZIPLIST_HEAD) ? ziplistHead(zl) : ziplistTail(zl);
if (*p == ZIP_END) return zl; if (*p == ZIP_END) return zl;
len = zipDecodeLength(p,&lensize);
prevrawlen = zipDecodeLength(p,&prevrawlensize);
len = zipDecodeLength(p+prevrawlensize,&lensize);
headerlen = prevrawlensize+lensize;
rawlen = headerlen+len;
if (target) { if (target) {
if (ZIP_ENCODING(p) == ZIP_ENC_RAW) { encoding = ZIP_ENCODING(p+prevrawlensize);
*target = sdsnewlen(p+lensize,len); if (encoding == ZIP_ENC_RAW) {
*target = sdsnewlen(p+headerlen,len);
} else { } else {
value = zipLoadInteger(p+lensize,ZIP_ENCODING(p)); value = zipLoadInteger(p+headerlen,encoding);
*target = sdscatprintf(sdsempty(), "%lld", value); *target = sdscatprintf(sdsempty(), "%lld", value);
} }
} }
/* Move list to front when popping from the head */
rawlen = lensize+len;
if (where == ZIPLIST_HEAD) { if (where == ZIPLIST_HEAD) {
memmove(p,p+rawlen,curlen-ZIPLIST_HEADER_SIZE-len); /* 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) -= prevrawlen;
} }
/* Resize and update length */ /* Resize and update length */
zl = ziplistResize(zl,curlen-rawlen); zl = ziplistResize(zl,curlen-rawlen+nextdiff);
ZIPLIST_INCR_LENGTH(zl,-1); ZIPLIST_INCR_LENGTH(zl,-1);
return zl; return zl;
} }
@ -307,18 +372,21 @@ unsigned char *ziplistNext(unsigned char *p) {
* to find out whether the string pointer or the integer value was set. * to find out whether the string pointer or the integer value was set.
* Return 0 if 'p' points to the end of the zipmap, 1 otherwise. */ * Return 0 if 'p' points to the end of the zipmap, 1 otherwise. */
unsigned int ziplistGet(unsigned char *p, unsigned char **e, unsigned int *elen, long long *v) { unsigned int ziplistGet(unsigned char *p, unsigned char **e, unsigned int *elen, long long *v) {
unsigned int len, lensize; unsigned int prevrawlensize, lensize, len, headerlen;
if (*p == ZIP_END) return 0; if (*p == ZIP_END) return 0;
if (e) *e = NULL; if (e) *e = NULL;
len = zipDecodeLength(p,&lensize);
if (ZIP_ENCODING(p) == ZIP_ENC_RAW) { zipDecodeLength(p,&prevrawlensize);
len = zipDecodeLength(p+prevrawlensize,&lensize);
headerlen = prevrawlensize+lensize;
if (ZIP_ENCODING(p+prevrawlensize) == ZIP_ENC_RAW) {
if (e) { if (e) {
*elen = len; *elen = len;
*e = p+lensize; *e = p+headerlen;
} }
} else { } else {
if (v) { if (v) {
*v = zipLoadInteger(p+lensize,ZIP_ENCODING(p)); *v = zipLoadInteger(p+headerlen,ZIP_ENCODING(p+prevrawlensize));
} }
} }
return 1; return 1;
@ -368,24 +436,26 @@ unsigned char *ziplistDelete(unsigned char *zl, unsigned char **p) {
/* Compare entry pointer to by 'p' with 'entry'. Return 1 if equal. */ /* Compare entry pointer to by 'p' with 'entry'. Return 1 if equal. */
unsigned int ziplistCompare(unsigned char *p, unsigned char *entry, unsigned int elen) { unsigned int ziplistCompare(unsigned char *p, unsigned char *entry, unsigned int elen) {
unsigned int zlen, lensize; unsigned int prevrawlensize, lensize, len, headerlen;
char encoding; char encoding;
long long zval, eval; long long val, eval;
if (*p == ZIP_END) return 0; if (*p == ZIP_END) return 0;
zlen = zipDecodeLength(p,&lensize); zipDecodeLength(p,&prevrawlensize);
if (ZIP_ENCODING(p) == ZIP_ENC_RAW) { len = zipDecodeLength(p+prevrawlensize,&lensize);
headerlen = prevrawlensize+lensize;
if (ZIP_ENCODING(p+prevrawlensize) == ZIP_ENC_RAW) {
/* Raw compare */ /* Raw compare */
if (zlen == elen) { if (len == elen) {
return memcmp(p+lensize,entry,elen) == 0; return memcmp(p+headerlen,entry,elen) == 0;
} else { } else {
return 0; return 0;
} }
} else { } else {
if (zipTryEncoding(entry,&eval,&encoding)) { if (zipTryEncoding(entry,&eval,&encoding)) {
/* Do integer compare */ /* Do integer compare */
zval = zipLoadInteger(p+lensize,ZIP_ENCODING(p)); val = zipLoadInteger(p+headerlen,ZIP_ENCODING(p+prevrawlensize));
return zval == eval; return val == eval;
} else { } else {
/* Ziplist entry is integer encoded, but given entry is not. */ /* Ziplist entry is integer encoded, but given entry is not. */
} }
@ -418,22 +488,23 @@ unsigned int ziplistSize(unsigned char *zl) {
void ziplistRepr(unsigned char *zl) { void ziplistRepr(unsigned char *zl) {
unsigned char *p, encoding; unsigned char *p, encoding;
unsigned int l, lsize; unsigned int prevrawlensize, prevrawlen, lensize, len;
printf("{total bytes %d} {length %u}\n",ZIPLIST_BYTES(zl), ZIPLIST_LENGTH(zl)); printf("{total bytes %d} {length %u}\n",ZIPLIST_BYTES(zl), ZIPLIST_LENGTH(zl));
p = ziplistHead(zl); p = ziplistHead(zl);
while(*p != ZIP_END) { while(*p != ZIP_END) {
l = zipDecodeLength(p,&lsize); prevrawlen = zipDecodeLength(p,&prevrawlensize);
printf("{header %u, payload %u} ",lsize,l); len = zipDecodeLength(p+prevrawlensize,&lensize);
encoding = ZIP_ENCODING(p); printf("{offset %ld, header %u, payload %u} ",p-zl,prevrawlensize+lensize,len);
p += lsize; encoding = ZIP_ENCODING(p+prevrawlensize);
p += prevrawlensize+lensize;
if (encoding == ZIP_ENC_RAW) { if (encoding == ZIP_ENC_RAW) {
fwrite(p,l,1,stdout); fwrite(p,len,1,stdout);
} else { } else {
printf("%lld", zipLoadInteger(p,encoding)); printf("%lld", zipLoadInteger(p,encoding));
} }
printf("\n"); printf("\n");
p += l; p += len;
} }
printf("{end}\n\n"); printf("{end}\n\n");
} }
@ -488,6 +559,14 @@ int main(int argc, char **argv) {
printf("Pop head: %s (length %ld)\n", s, sdslen(s)); printf("Pop head: %s (length %ld)\n", s, sdslen(s));
ziplistRepr(zl); ziplistRepr(zl);
zl = ziplistPop(zl, &s, ZIPLIST_TAIL);
printf("Pop tail: %s (length %ld)\n", s, sdslen(s));
ziplistRepr(zl);
zl = ziplistPop(zl, &s, ZIPLIST_TAIL);
printf("Pop tail: %s (length %ld)\n", s, sdslen(s));
ziplistRepr(zl);
printf("Iterate list from 0 to end:\n"); printf("Iterate list from 0 to end:\n");
{ {
zl = createList(); zl = createList();
@ -614,21 +693,21 @@ int main(int argc, char **argv) {
zl = createList(); zl = createList();
p = ziplistIndex(zl, 0); p = ziplistIndex(zl, 0);
if (!ziplistCompare(p,"hello",5)) { if (!ziplistCompare(p,"hello",5)) {
printf("ERROR\n"); printf("ERROR: not \"hello\"\n");
return; return;
} }
if (ziplistCompare(p,"hella",5)) { if (ziplistCompare(p,"hella",5)) {
printf("ERROR\n"); printf("ERROR: \"hella\"\n");
return; return;
} }
p = ziplistIndex(zl, 3); p = ziplistIndex(zl, 3);
if (!ziplistCompare(p,"1024",4)) { if (!ziplistCompare(p,"1024",4)) {
printf("ERROR\n"); printf("ERROR: not \"1024\"\n");
return; return;
} }
if (ziplistCompare(p,"1025",4)) { if (ziplistCompare(p,"1025",4)) {
printf("ERROR\n"); printf("ERROR: \"1025\"\n");
return; return;
} }
printf("SUCCESS\n"); printf("SUCCESS\n");