/* Memory layout of a ziplist, containing "foo", "bar", "quux":
* <zlbytes><zllen><len>"foo"<len>"bar"<len>"quux"
*
* <zlbytes> is an unsigned integer to hold the number of bytes that
* the ziplist occupies. This is stored to not have to traverse the ziplist
* to know the new length when pushing.
*
* <zllen> is the number of items in the ziplist. When this value is
* greater than 254, we need to traverse the entire list to know
* how many items it holds.
*
* <len> is the number of bytes occupied by a single entry. When this
* number is greater than 253, the length will occupy 5 bytes, where
* the extra bytes contain an unsigned integer to hold the length.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <limits.h>
#include "zmalloc.h"
#include "sds.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_BIGLEN 254
/* Entry encoding */
#define ZIP_ENC_RAW 0
#define ZIP_ENC_SHORT 1
#define ZIP_ENC_INT 2
#define ZIP_ENC_LLONG 3
#define ZIP_ENCODING(p) ((p)[0] >> 6)
/* Length encoding for raw entries */
#define ZIP_LEN_INLINE 0
#define ZIP_LEN_UINT16 1
#define ZIP_LEN_UINT32 2
/* Utility macros */
#define ZIPLIST_BYTES(zl) (*((unsigned int*)(zl)))
#define ZIPLIST_TAIL_OFFSET(zl) (*((zl)+sizeof(unsigned int)))
#define ZIPLIST_LENGTH(zl) (*((zl)+2*sizeof(unsigned int)))
#define ZIPLIST_HEADER_SIZE (2*sizeof(unsigned int)+1)
#define ZIPLIST_INCR_LENGTH(zl,incr) { \
if (ZIPLIST_LENGTH(zl) < ZIP_BIGLEN) ZIPLIST_LENGTH(zl)+=incr; }
/* Return bytes needed to store integer encoded by 'encoding' */
static unsigned int zipEncodingSize(char encoding) {
if (encoding == ZIP_ENC_SHORT) {
return sizeof(short int);
} else if (encoding == ZIP_ENC_INT) {
return sizeof(int);
} else if (encoding == ZIP_ENC_LLONG) {
return sizeof(long long);
}
assert(NULL);
}
/* Decode the encoded length pointed by 'p'. If a pointer to 'lensize' is
* provided, it is set to the number of bytes required to encode the length. */
static unsigned int zipDecodeLength(unsigned char *p, unsigned int *lensize) {
unsigned char encoding = ZIP_ENCODING(p), lenenc;
unsigned int len;
if (encoding == ZIP_ENC_RAW) {
lenenc = (p[0] >> 4) & 0x3;
if (lenenc == ZIP_LEN_INLINE) {
len = p[0] & 0xf;
if (lensize) *lensize = 1;
} else if (lenenc == ZIP_LEN_UINT16) {
len = p[1] | (p[2] << 8);
if (lensize) *lensize = 3;
} else {
len = p[1] | (p[2] << 8) | (p[3] << 16) | (p[4] << 24);
if (lensize) *lensize = 5;
}
} else {
len = zipEncodingSize(encoding);
if (lensize) *lensize = 1;
}
return len;
}
/* Encode the length 'l' writing it in 'p'. If p is NULL it just returns
* the amount of bytes required to encode such a length. */
static unsigned int zipEncodeLength(unsigned char *p, char encoding, unsigned int rawlen) {
unsigned char len = 1, lenenc, buf[5];
if (encoding == ZIP_ENC_RAW) {
if (rawlen <= 0xf) {
if (!p) return len;
lenenc = ZIP_LEN_INLINE;
buf[0] = rawlen;
} else if (rawlen <= 0xffff) {
len += 2;
if (!p) return len;
lenenc = ZIP_LEN_UINT16;
buf[1] = (rawlen ) & 0xff;
buf[2] = (rawlen >> 8) & 0xff;
} else {
len += 4;
if (!p) return len;
lenenc = ZIP_LEN_UINT32;
buf[1] = (rawlen ) & 0xff;
buf[2] = (rawlen >> 8) & 0xff;
buf[3] = (rawlen >> 16) & 0xff;
buf[4] = (rawlen >> 24) & 0xff;
}
buf[0] = (lenenc << 4) | (buf[0] & 0xf);
}
if (!p) return len;
/* Apparently we need to store the length in 'p' */
buf[0] = (encoding << 6) | (buf[0] & 0x3f);
memcpy(p,buf,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.
* Stores the integer value in 'v' and its encoding in 'encoding'.
* Warning: this function requires a NULL-terminated string! */
static int zipTryEncoding(unsigned char *entry, long long *v, char *encoding) {
long long value;
char *eptr;
if (entry[0] == '-' || (entry[0] >= '0' && entry[0] <= '9')) {
value = strtoll((char*)entry,&eptr,10);
if (eptr[0] != '\0') return 0;
if (value >= SHRT_MIN && value <= SHRT_MAX) {
*encoding = ZIP_ENC_SHORT;
} else if (value >= INT_MIN && value <= INT_MAX) {
*encoding = ZIP_ENC_INT;
} else {
*encoding = ZIP_ENC_LLONG;
}
*v = value;
return 1;
}
return 0;
}
/* Store integer 'value' at 'p', encoded as 'encoding' */
static void zipSaveInteger(unsigned char *p, long long value, char encoding) {
short int s;
int i;
long long l;
if (encoding == ZIP_ENC_SHORT) {
s = value;
memcpy(p,&s,sizeof(s));
} else if (encoding == ZIP_ENC_INT) {
i = value;
memcpy(p,&i,sizeof(i));
} else if (encoding == ZIP_ENC_LLONG) {
l = value;
memcpy(p,&l,sizeof(l));
} else {
assert(NULL);
}
}
/* Read integer encoded as 'encoding' from 'p' */
static long long zipLoadInteger(unsigned char *p, char encoding) {
short int s;
int i;
long long l, ret;
if (encoding == ZIP_ENC_SHORT) {
memcpy(&s,p,sizeof(s));
ret = s;
} else if (encoding == ZIP_ENC_INT) {
memcpy(&i,p,sizeof(i));
ret = i;
} else if (encoding == ZIP_ENC_LLONG) {
memcpy(&l,p,sizeof(l));
ret = l;
} else {
assert(NULL);
}
return ret;
}
/* Return the total amount used by an entry (encoded length + payload). */
static unsigned int zipRawEntryLength(unsigned char *p) {
unsigned int prevlensize, lensize, len;
/* Byte-size of encoded length of previous entry */
zipDecodeLength(p,&prevlensize);
/* Encoded length of this entry's payload */
len = zipDecodeLength(p+prevlensize, &lensize);
return prevlensize+lensize+len;
}
/* Create a new empty ziplist. */
unsigned char *ziplistNew(void) {
unsigned int bytes = ZIPLIST_HEADER_SIZE+1;
unsigned char *zl = zmalloc(bytes);
ZIPLIST_BYTES(zl) = bytes;
ZIPLIST_TAIL_OFFSET(zl) = ZIPLIST_HEADER_SIZE;
ZIPLIST_LENGTH(zl) = 0;
zl[bytes-1] = ZIP_END;
return zl;
}
/* Resize the ziplist. */
static unsigned char *ziplistResize(unsigned char *zl, unsigned int len) {
zl = zrealloc(zl,len);
ZIPLIST_BYTES(zl) = len;
zl[len-1] = ZIP_END;
return zl;
}
static unsigned char *ziplistHead(unsigned char *zl) {
return zl+ZIPLIST_HEADER_SIZE;
}
static unsigned char *ziplistTail(unsigned char *zl) {
unsigned char *p, *q;
p = q = ziplistHead(zl);
while (*p != ZIP_END) {
q = p;
p += zipRawEntryLength(p);
}
return q;
}
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;
char encoding = ZIP_ENC_RAW;
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 */
if (zipTryEncoding(entry,&value,&encoding)) {
reqlen = zipEncodingSize(encoding);
} else {
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);
/* 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);
}
} 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;
}
}
/* Write the entry */
p += zipEncodeLength(p,ZIP_ENC_RAW,prevlen);
p += zipEncodeLength(p,encoding,elen);
if (encoding != ZIP_ENC_RAW) {
zipSaveInteger(p,value,encoding);
} else {
memcpy(p,entry,elen);
}
ZIPLIST_INCR_LENGTH(zl,1);
return zl;
}
unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
unsigned int curlen = ZIPLIST_BYTES(zl), rawlen;
unsigned int prevrawlensize, prevrawlen, lensize, len, headerlen;
int nextdiff = 0;
unsigned char encoding;
unsigned char *p;
long long value;
if (target) *target = NULL;
/* Get pointer to element to remove */
p = (where == ZIPLIST_HEAD) ? ziplistHead(zl) : ziplistTail(zl);
if (*p == ZIP_END) return zl;
prevrawlen = zipDecodeLength(p,&prevrawlensize);
len = zipDecodeLength(p+prevrawlensize,&lensize);
headerlen = prevrawlensize+lensize;
rawlen = headerlen+len;
if (target) {
encoding = ZIP_ENCODING(p+prevrawlensize);
if (encoding == ZIP_ENC_RAW) {
*target = sdsnewlen(p+headerlen,len);
} else {
value = zipLoadInteger(p+headerlen,encoding);
*target = sdscatprintf(sdsempty(), "%lld", value);
}
}
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) -= prevrawlen;
}
/* Resize and update length */
zl = ziplistResize(zl,curlen-rawlen+nextdiff);
ZIPLIST_INCR_LENGTH(zl,-1);
return zl;
}
/* Returns an offset to use for iterating with ziplistNext. */
unsigned char *ziplistIndex(unsigned char *zl, unsigned int index) {
unsigned char *p = zl+ZIPLIST_HEADER_SIZE;
unsigned int i = 0;
for (; i < index; i++) {
if (*p == ZIP_END) break;
p += zipRawEntryLength(p);
}
return p;
}
/* Return pointer to next entry in ziplist. */
unsigned char *ziplistNext(unsigned char *p) {
return *p == ZIP_END ? p : p+zipRawEntryLength(p);
}
/* Get entry pointer to by 'p' and store in either 'e' or 'v' depending
* on the encoding of the entry. 'e' is always set to NULL to be able
* 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. */
unsigned int ziplistGet(unsigned char *p, unsigned char **e, unsigned int *elen, long long *v) {
unsigned int prevrawlensize, lensize, len, headerlen;
if (*p == ZIP_END) return 0;
if (e) *e = NULL;
zipDecodeLength(p,&prevrawlensize);
len = zipDecodeLength(p+prevrawlensize,&lensize);
headerlen = prevrawlensize+lensize;
if (ZIP_ENCODING(p+prevrawlensize) == ZIP_ENC_RAW) {
if (e) {
*elen = len;
*e = p+headerlen;
}
} else {
if (v) {
*v = zipLoadInteger(p+headerlen,ZIP_ENCODING(p+prevrawlensize));
}
}
return 1;
}
/* 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;
}
/* 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);
/* Store new pointer to current element in p.
* This needs to be done because zl can change on realloc. */
*p = zl+offset;
return zl;
}
/* 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 prevrawlensize, lensize, len, headerlen;
char encoding;
long long val, eval;
if (*p == ZIP_END) return 0;
zipDecodeLength(p,&prevrawlensize);
len = zipDecodeLength(p+prevrawlensize,&lensize);
headerlen = prevrawlensize+lensize;
if (ZIP_ENCODING(p+prevrawlensize) == ZIP_ENC_RAW) {
/* Raw compare */
if (len == elen) {
return memcmp(p+headerlen,entry,elen) == 0;
} else {
return 0;
}
} else {
if (zipTryEncoding(entry,&eval,&encoding)) {
/* Do integer compare */
val = zipLoadInteger(p+headerlen,ZIP_ENCODING(p+prevrawlensize));
return val == eval;
} else {
/* Ziplist entry is integer encoded, but given entry is not. */
}
}
return 0;
}
/* Return length of ziplist. */
unsigned int ziplistLen(unsigned char *zl) {
unsigned int len = 0;
if (ZIPLIST_LENGTH(zl) < ZIP_BIGLEN) {
len = ZIPLIST_LENGTH(zl);
} else {
unsigned char *p = zl+ZIPLIST_HEADER_SIZE;
while (*p != ZIP_END) {
p += zipRawEntryLength(p);
len++;
}
/* Re-store length if small enough */
if (len < ZIP_BIGLEN) ZIPLIST_LENGTH(zl) = len;
}
return len;
}
/* Return size in bytes of ziplist. */
unsigned int ziplistSize(unsigned char *zl) {
return ZIPLIST_BYTES(zl);
}
void ziplistRepr(unsigned char *zl) {
unsigned char *p, encoding;
unsigned int prevrawlensize, prevrawlen, lensize, len;
printf("{total bytes %d} {length %u}\n",ZIPLIST_BYTES(zl), ZIPLIST_LENGTH(zl));
p = ziplistHead(zl);
while(*p != ZIP_END) {
prevrawlen = zipDecodeLength(p,&prevrawlensize);
len = zipDecodeLength(p+prevrawlensize,&lensize);
printf("{offset %ld, header %u, payload %u} ",p-zl,prevrawlensize+lensize,len);
encoding = ZIP_ENCODING(p+prevrawlensize);
p += prevrawlensize+lensize;
if (encoding == ZIP_ENC_RAW) {
fwrite(p,len,1,stdout);
} else {
printf("%lld", zipLoadInteger(p,encoding));
}
printf("\n");
p += len;
}
printf("{end}\n\n");
}
#ifdef ZIPLIST_TEST_MAIN
unsigned char *createList() {
unsigned char *zl = ziplistNew();
zl = ziplistPush(zl, (unsigned char*)"foo", 3, ZIPLIST_TAIL);
zl = ziplistPush(zl, (unsigned char*)"quux", 4, ZIPLIST_TAIL);
zl = ziplistPush(zl, (unsigned char*)"hello", 5, ZIPLIST_HEAD);
zl = ziplistPush(zl, (unsigned char*)"1024", 4, ZIPLIST_TAIL);
return zl;
}
unsigned char *createIntList() {
unsigned char *zl = ziplistNew();
char buf[32];
sprintf(buf, "100");
zl = ziplistPush(zl, buf, strlen(buf), ZIPLIST_TAIL);
sprintf(buf, "128000");
zl = ziplistPush(zl, buf, strlen(buf), ZIPLIST_TAIL);
sprintf(buf, "-100");
zl = ziplistPush(zl, buf, strlen(buf), ZIPLIST_HEAD);
sprintf(buf, "4294967296");
zl = ziplistPush(zl, buf, strlen(buf), ZIPLIST_HEAD);
sprintf(buf, "non integer");
zl = ziplistPush(zl, buf, strlen(buf), ZIPLIST_TAIL);
sprintf(buf, "much much longer non integer");
zl = ziplistPush(zl, buf, strlen(buf), ZIPLIST_TAIL);
return zl;
}
int main(int argc, char **argv) {
unsigned char *zl, *p, *q, *entry;
unsigned int elen;
long long value;
sds s;
zl = createIntList();
ziplistRepr(zl);
zl = createList();
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_HEAD);
printf("Pop head: %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);
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");
{
zl = createList();
p = ziplistIndex(zl, 0);
while (ziplistGet(p, &entry, &elen, &value)) {
printf("Entry: ");
if (entry) {
fwrite(entry,elen,1,stdout);
} else {
printf("%lld", value);
}
p = ziplistNext(p);
printf("\n");
}
printf("\n");
}
printf("Iterate list from 1 to end:\n");
{
zl = createList();
p = ziplistIndex(zl, 1);
while (ziplistGet(p, &entry, &elen, &value)) {
printf("Entry: ");
if (entry) {
fwrite(entry,elen,1,stdout);
} else {
printf("%lld", value);
}
p = ziplistNext(p);
printf("\n");
}
printf("\n");
}
printf("Iterate list from 2 to end:\n");
{
zl = createList();
p = ziplistIndex(zl, 2);
while (ziplistGet(p, &entry, &elen, &value)) {
printf("Entry: ");
if (entry) {
fwrite(entry,elen,1,stdout);
} else {
printf("%lld", value);
}
p = ziplistNext(p);
printf("\n");
}
printf("\n");
}
printf("Iterate starting out of range:\n");
{
zl = createList();
p = ziplistIndex(zl, 4);
if (!ziplistGet(p, &entry, &elen, &value)) {
printf("No entry\n");
} else {
printf("ERROR\n");
}
printf("\n");
}
printf("Delete inclusive range 0,0:\n");
{
zl = createList();
zl = ziplistDeleteRange(zl, 0, 1);
ziplistRepr(zl);
}
printf("Delete inclusive range 0,1:\n");
{
zl = createList();
zl = ziplistDeleteRange(zl, 0, 2);
ziplistRepr(zl);
}
printf("Delete inclusive range 1,2:\n");
{
zl = createList();
zl = ziplistDeleteRange(zl, 1, 2);
ziplistRepr(zl);
}
printf("Delete with start index out of range:\n");
{
zl = createList();
zl = ziplistDeleteRange(zl, 5, 1);
ziplistRepr(zl);
}
printf("Delete with num overflow:\n");
{
zl = createList();
zl = ziplistDeleteRange(zl, 1, 5);
ziplistRepr(zl);
}
printf("Delete foo while iterating:\n");
{
zl = createList();
p = ziplistIndex(zl, 0);
while (ziplistGet(p, &entry, &elen, &value)) {
if (entry && strncmp("foo", entry, elen) == 0) {
printf("Delete foo\n");
zl = ziplistDelete(zl, &p);
} else {
printf("Entry: ");
if (entry) {
fwrite(entry,elen,1,stdout);
} else {
printf("%lld", value);
}
p = ziplistNext(p);
printf("\n");
}
}
printf("\n");
ziplistRepr(zl);
}
printf("Compare strings with ziplist entries:\n");
{
zl = createList();
p = ziplistIndex(zl, 0);
if (!ziplistCompare(p,"hello",5)) {
printf("ERROR: not \"hello\"\n");
return;
}
if (ziplistCompare(p,"hella",5)) {
printf("ERROR: \"hella\"\n");
return;
}
p = ziplistIndex(zl, 3);
if (!ziplistCompare(p,"1024",4)) {
printf("ERROR: not \"1024\"\n");
return;
}
if (ziplistCompare(p,"1025",4)) {
printf("ERROR: \"1025\"\n");
return;
}
printf("SUCCESS\n");
}
return 0;
}
#endif