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ruanhaishen
redis
Commits
97bde9f6
Commit
97bde9f6
authored
Mar 11, 2018
by
Otmar Ertl
Browse files
use all 64 bits of the hash value instead of 63
parent
44698f45
Changes
1
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Inline
Side-by-side
src/hyperloglog.c
View file @
97bde9f6
...
...
@@ -192,11 +192,12 @@ struct hllhdr {
#define HLL_VALID_CACHE(hdr) (((hdr)->card[7] & (1<<7)) == 0)
#define HLL_P 14
/* The greater is P, the smaller the error. */
#define HLL_Q (64-HLL_P)
/* The number of bits of the hash value used for
determining the number of leading zeros. */
#define HLL_REGISTERS (1<<HLL_P)
/* With P=14, 16384 registers. */
#define HLL_P_MASK (HLL_REGISTERS-1)
/* Mask to index register. */
#define HLL_BITS 6
/* Enough to count up to 63 leading zeroes. */
#define HLL_REGISTER_MAX ((1<<HLL_BITS)-1)
#define HLL_Q (HLL_REGISTER_MAX-HLL_P)
#define HLL_HDR_SIZE sizeof(struct hllhdr)
#define HLL_DENSE_SIZE (HLL_HDR_SIZE+((HLL_REGISTERS*HLL_BITS+7)/8))
#define HLL_DENSE 0
/* Dense encoding. */
...
...
@@ -452,7 +453,7 @@ int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
/* Count the number of zeroes starting from bit HLL_REGISTERS
* (that is a power of two corresponding to the first bit we don't use
* as index). The max run can be 64-P+1 bits.
* as index). The max run can be 64-P+1
= Q+1
bits.
*
* Note that the final "1" ending the sequence of zeroes must be
* included in the count, so if we find "001" the count is 3, and
...
...
@@ -463,8 +464,10 @@ int hllPatLen(unsigned char *ele, size_t elesize, long *regp) {
* there are high probabilities to find a 1 after a few iterations. */
hash
=
MurmurHash64A
(
ele
,
elesize
,
0xadc83b19ULL
);
index
=
hash
&
HLL_P_MASK
;
/* Register index. */
hash
|=
((
uint64_t
)
1
<<
63
);
/* Make sure the loop terminates. */
bit
=
HLL_REGISTERS
;
/* First bit not used to address the register. */
hash
>>=
HLL_P
;
/* Remove bits used to address the register. */
hash
|=
((
uint64_t
)
1
<<
HLL_Q
);
/* Make sure the loop terminates
and count will be <= Q+1. */
bit
=
1
;
count
=
1
;
/* Initialized to 1 since we count the "00000...1" pattern. */
while
((
hash
&
bit
)
==
0
)
{
count
++
;
...
...
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