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HyperLogLog sparse to dense conversion function.

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antirez 2014-04-12 10:55:28 +02:00
parent c756936b1d
commit 1fc04a6221
1 changed files with 44 additions and 3 deletions
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47
src/hyperloglog.c
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@ -202,6 +202,8 @@ struct hllhdr {
#define HLL_SPARSE 1 /* Sparse encoding */
#define HLL_MAX_ENCODING 1
#define HLL_SPARSE_MAX 3000
/* =========================== Low level bit macros ========================= */
/* Macros to access the dense representation.
@ -555,8 +557,46 @@ double hllDenseSum(uint8_t *registers, double *PE, int *ezp) {
/* ================== Sparse representation implementation ================= */
sds hllSparseToDense(sds *sparse) {
return sdsnew("TODO");
/* Convert the HLL with sparse representation given as input in its dense
* representation. Both representations are represented by SDS strings, and
* the input representation is freed as a side effect. */
sds hllSparseToDense(sds sparse) {
sds dense;
struct hllhdr *hdr, *oldhdr = (struct hllhdr*)sparse;
int idx = 0, runlen, regval;
uint8_t *p = (uint8_t*)sparse, *end = p+sdslen(sparse);
/* 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. */
dense = sdsnewlen(NULL,HLL_DENSE_SIZE);
hdr = (struct hllhdr*) dense;
*hdr = *oldhdr; /* This will copy the magic and cached cardinality. */
hdr->encoding = HLL_DENSE;
/* Now read the sparse representation and set non-zero registers
* accordingly. */
p += HLL_HDR_SIZE;
while(p < end) {
if (HLL_SPARSE_IS_ZERO(p)) {
runlen = HLL_SPARSE_ZERO_LEN(p);
idx += runlen;
} else if (HLL_SPARSE_IS_XZERO(p)) {
runlen = HLL_SPARSE_XZERO_LEN(p);
idx += runlen;
} else {
runlen = HLL_SPARSE_VAL_LEN(p);
regval = HLL_SPARSE_VAL_VALUE(p);
while(runlen--) {
HLL_DENSE_SET_REGISTER(hdr->registers,idx,regval);
idx++;
}
}
}
/* Free the old representation and return the new one. */
sdsfree(sparse);
return dense;
}
/* "Add" the element in the sparse hyperloglog data structure.
@ -739,6 +779,8 @@ int hllSparseAdd(robj *o, unsigned char *ele, size_t elesize) {
int seqlen = seq-n;
int oldlen = is_xzero ? 2 : 1;
int deltalen = seqlen-oldlen;
if (deltalen > 0 && sdslen(o->ptr) > HLL_SPARSE_MAX) goto promote;
if (deltalen && next) {
memmove(next+deltalen,next,next-sparse);
sdsIncrLen(o->ptr,deltalen);
@ -774,7 +816,6 @@ double hllSparseSum(uint8_t *sparse, int sparselen, double *PE, int *ezp) {
uint8_t *end = sparse+sparselen, *p = sparse;
while(p < end) {
/* Set span to the number of registers covered by this opcode. */
if (HLL_SPARSE_IS_ZERO(p)) {
runlen = HLL_SPARSE_ZERO_LEN(p);
idx += runlen;