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Merge adjacent VAL opcodes in hllSparseAdd().

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As more values are added splitting ZERO or XZERO opcodes, try to merge
adjacent VAL opcodes if they have the same value.
This commit is contained in:
antirez 2014-04-14 12:09:37 +02:00
parent 837ca39081
commit 5532b5308a
1 changed files with 36 additions and 5 deletions
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41
src/hyperloglog.c
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@ -805,16 +805,47 @@ int hllSparseAdd(robj *o, unsigned char *ele, size_t elesize) {
if (deltalen && next) memmove(next+deltalen,next,end-next);
sdsIncrLen(o->ptr,deltalen);
memcpy(p,seq,seqlen);
end += deltalen;
updated:
/* Step 4: Merge adjacent values if possible.
*
* The representation was updated, however the resulting representation
* may not be optimal: adjacent opcodes may be merged into a single one.
* We start from the opcode before the one we updated trying to merge
* opcodes up to the next 5 opcodes (since we need to consider the three
* opcodes resuling from the worst-case split of the updated opcode,
* plus the two opcodes at the left and right of the original one). */
* may not be optimal: adjacent VAL opcodes can sometimes be merged into
* a single one. */
p = prev ? prev : sparse;
int scanlen = 5; /* Scan up to 5 upcodes starting from prev. */
while (p < end && scanlen--) {
if (HLL_SPARSE_IS_XZERO(p)) {
p += 2;
continue;
} else if (HLL_SPARSE_IS_ZERO(p)) {
p++;
continue;
}
/* We need two adjacent VAL opcodes to try a merge, having
* the same value, and a len that first the VAL opcode max len. */
if (p+1 < end && HLL_SPARSE_IS_VAL(p+1)) {
int v1 = HLL_SPARSE_VAL_VALUE(p);
int v2 = HLL_SPARSE_VAL_VALUE(p+1);
if (v1 == v2) {
int len = HLL_SPARSE_VAL_LEN(p)+HLL_SPARSE_VAL_LEN(p+1);
if (len <= HLL_SPARSE_VAL_MAX_LEN) {
HLL_SPARSE_VAL_SET(p+1,v1,len);
memmove(p,p+1,end-p);
sdsIncrLen(o->ptr,-1);
end--;
/* After a merge we reiterate without incrementing 'p'
* in order to try to merge the just merged value with
* a value on its right. */
continue;
}
}
}
p++;
}
/* Invalidate the cached cardinality. */
hdr = o->ptr;
HLL_INVALIDATE_CACHE(hdr);
return 1;