blob: 31e0ea22541b35081409bb90f53ad2b9e50e7207 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
|
/*
* Copyright (c) 2011-Present, Redis Ltd.
* All rights reserved.
*
* Licensed under your choice of (a) the Redis Source Available License 2.0
* (RSALv2); or (b) the Server Side Public License v1 (SSPLv1); or (c) the
* GNU Affero General Public License v3 (AGPLv3).
*
*
* FENWICK TREE (Binary Indexed Tree)
* ----------------------------------
* A Fenwick tree is a data structure that efficiently supports:
* - Point updates: Add/subtract values at specific indices in O(log n) time
* - Prefix sum queries: Calculate cumulative sums from index 0 to any index in O(log n) time
* - Range queries: Calculate sums over any range [i,j] in O(log n) time
* - Space complexity: O(n)
*
* USAGE IN REDIS
* --------------
* This implementation is used by KVSTORE and ESTORE to efficiently track:
* - Cumulative key counts across dictionary slots (KVSTORE)
* - Cumulative item counts across expiration buckets (ESTORE)
*
* This enables efficient operations like:
* - Finding which dictionary/bucket contains the Nth key/item
* - Iterating through non-empty dictionaries/buckets
* - Load balancing and random key selection
*
* IMPLEMENTATION NOTES
* -------------------
* - The tree uses 1-based indexing internally for mathematical convenience
* - The public API uses 0-based indexing for consistency with Redis codebase
* - Tree size must be a power of 2 (specified as sizeBits where size = 2^sizeBits)
* - All operations have O(log n) time complexity where n is the tree size
*
* REFERENCES
* ----------
* For more details on Fenwick trees: https://en.wikipedia.org/wiki/Fenwick_tree
*/
#ifndef __FWTREE_H
#define __FWTREE_H
#include <stdint.h>
/* Forward declaration of the fenwick tree structure */
typedef struct _fenwickTree fenwickTree;
/* Fenwick Tree API */
fenwickTree *fwTreeCreate(int sizeBits);
void fwTreeDestroy(fenwickTree *ft);
unsigned long long fwTreePrefixSum(fenwickTree *ft, int idx);
void fwTreeUpdate(fenwickTree *ft, int idx, long long delta);
int fwTreeFindIndex(fenwickTree *ft, unsigned long long target);
int fwTreeFindFirstNonEmpty(fenwickTree *ft);
int fwTreeFindNextNonEmpty(fenwickTree *ft, int idx);
void fwTreeClear(fenwickTree *ft);
#ifdef REDIS_TEST
int fwtreeTest(int argc, char *argv[], int flags);
#endif
#endif /* __FWTREE_H */
|
