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Create HyperLogLog objects with sparse encoding.

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antirez 2014-04-12 10:56:11 +02:00
parent 1fc04a6221
commit a79386b1af
1 changed files with 28 additions and 10 deletions
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38
src/hyperloglog.c
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@ -905,19 +905,37 @@ uint64_t hllCount(struct hllhdr *hdr) {
/* ========================== HyperLogLog commands ========================== */
/* An HyperLogLog object is a string with space for 16k 6-bit integers,
* a cached 64 bit cardinality value, and a 4 byte "magic" and additional
* 4 bytes for version reserved for future use. */
/* Create an HLL object. We always create the HLL using sparse encoding.
* This will be upgraded to the dense representation as needed. */
robj *createHLLObject(void) {
robj *o;
char *p;
struct hllhdr *hdr;
sds s;
uint8_t *p;
int sparselen = HLL_HDR_SIZE +
((HLL_REGISTERS+(HLL_SPARSE_XZERO_MAX_LEN-1)) /
HLL_SPARSE_XZERO_MAX_LEN);
int aux;
/* Create a string of the right size filled with zero bytes.
* Note that the cached cardinality is set to 0 as a side effect
* that is exactly the cardinality of an empty HLL. */
o = createObject(REDIS_STRING,sdsnewlen(NULL,HLL_DENSE_SIZE));
p = o->ptr;
memcpy(p,"HYLL",4);
/* Populate the sparse representation with as many XZERO opcodes as
* needed to represent all the registers. */
aux = sparselen;
s = sdsnewlen(NULL,sparselen);
p = (uint8_t*)s + HLL_HDR_SIZE;
while(aux) {
int xzero = HLL_SPARSE_XZERO_MAX_LEN-1;
if (xzero > aux) xzero = aux;
HLL_SPARSE_XZERO_SET(p,xzero);
p += 2;
aux -= xzero;
}
redisAssert((p-(uint8_t*)s) == sparselen);
/* Create the actual object. */
o = createObject(REDIS_STRING,s);
hdr = o->ptr;
memcpy(hdr->magic,"HYLL",4);
hdr->encoding = HLL_SPARSE;
return o;
}