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Code Issues Releases Wiki Activity

ziplistIndex now accepts negative indices

This commit is contained in:
Pieter Noordhuis 2010-05-29 22:17:16 +02:00
parent a24ba809d1
commit c03206fdf1
2 changed files with 102 additions and 11 deletions
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111
ziplist.c
View File

@ -402,15 +402,29 @@ unsigned char *ziplistPop(unsigned char *zl, sds *target, int where) {
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);
/* Returns an offset to use for iterating with ziplistNext. When the given
* index is negative, the list is traversed back to front. When the list
* doesn't contain an element at the provided index, NULL is returned. */
unsigned char *ziplistIndex(unsigned char *zl, int index) {
unsigned char *p;
zlentry entry;
if (index < 0) {
index = (-index)-1;
p = ZIPLIST_ENTRY_TAIL(zl);
if (p[0] != ZIP_END) {
entry = zipEntry(p);
while (entry.prevrawlen > 0 && index--) {
p -= entry.prevrawlen;
entry = zipEntry(p);
}
}
} else {
p = ZIPLIST_ENTRY_HEAD(zl);
while (p[0] != ZIP_END && index--) {
p += zipRawEntryLength(p);
}
}
return p;
return p[0] == ZIP_END || index > 0 ? NULL : p;
}
/* Return pointer to next entry in ziplist. */
@ -424,7 +438,7 @@ unsigned char *ziplistNext(unsigned char *p) {
* Return 0 if 'p' points to the end of the zipmap, 1 otherwise. */
unsigned int ziplistGet(unsigned char *p, char **sstr, unsigned int *slen, long long *sval) {
zlentry entry;
if (*p == ZIP_END) return 0;
if (p == NULL || p[0] == ZIP_END) return 0;
if (sstr) *sstr = NULL;
entry = zipEntry(p);
@ -444,7 +458,7 @@ unsigned int ziplistGet(unsigned char *p, char **sstr, unsigned int *slen, long
/* Delete a range of entries from the ziplist. */
unsigned char *ziplistDeleteRange(unsigned char *zl, unsigned int index, unsigned int num) {
unsigned char *p = ziplistIndex(zl,index);
return __ziplistDelete(zl,p,num);
return p == NULL ? zl : __ziplistDelete(zl,p,num);
}
/* Delete a single entry from the ziplist, pointed to by *p.
@ -590,6 +604,83 @@ int main(int argc, char **argv) {
printf("Pop tail: %s (length %ld)\n", s, sdslen(s));
ziplistRepr(zl);
printf("Get element at index 3:\n");
{
zl = createList();
p = ziplistIndex(zl, 3);
if (!ziplistGet(p, &entry, &elen, &value)) {
printf("ERROR: Could not access index 3\n");
return 1;
}
if (entry) {
fwrite(entry,elen,1,stdout);
printf("\n");
} else {
printf("%lld\n", value);
}
printf("\n");
}
printf("Get element at index 4 (out of range):\n");
{
zl = createList();
p = ziplistIndex(zl, 4);
if (p == NULL) {
printf("No entry\n");
} else {
printf("ERROR: Out of range index should return NULL, returned offset: %ld\n", p-zl);
return 1;
}
printf("\n");
}
printf("Get element at index -1 (last element):\n");
{
zl = createList();
p = ziplistIndex(zl, -1);
if (!ziplistGet(p, &entry, &elen, &value)) {
printf("ERROR: Could not access index -1\n");
return 1;
}
if (entry) {
fwrite(entry,elen,1,stdout);
printf("\n");
} else {
printf("%lld\n", value);
}
printf("\n");
}
printf("Get element at index -4 (first element):\n");
{
zl = createList();
p = ziplistIndex(zl, -4);
if (!ziplistGet(p, &entry, &elen, &value)) {
printf("ERROR: Could not access index -4\n");
return 1;
}
if (entry) {
fwrite(entry,elen,1,stdout);
printf("\n");
} else {
printf("%lld\n", value);
}
printf("\n");
}
printf("Get element at index -5 (reverse out of range):\n");
{
zl = createList();
p = ziplistIndex(zl, -5);
if (p == NULL) {
printf("No entry\n");
} else {
printf("ERROR: Out of range index should return NULL, returned offset: %ld\n", p-zl);
return 1;
}
printf("\n");
}
printf("Iterate list from 0 to end:\n");
{
zl = createList();

2
ziplist.h
View File

@ -4,7 +4,7 @@
unsigned char *ziplistNew(void);
unsigned char *ziplistPush(unsigned char *zl, char *s, unsigned int slen, int where);
unsigned char *ziplistPop(unsigned char *zl, sds *target, int where);
unsigned char *ziplistIndex(unsigned char *zl, unsigned int index);
unsigned char *ziplistIndex(unsigned char *zl, int index);
unsigned char *ziplistNext(unsigned char *p);
unsigned int ziplistGet(unsigned char *p, char **sstr, unsigned int *slen, long long *sval);
unsigned char *ziplistDelete(unsigned char *zl, unsigned char **p);