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1 /* | |
2 ** 2001 September 22 | |
3 ** | |
4 ** The author disclaims copyright to this source code. In place of | |
5 ** a legal notice, here is a blessing: | |
6 ** | |
7 ** May you do good and not evil. | |
8 ** May you find forgiveness for yourself and forgive others. | |
9 ** May you share freely, never taking more than you give. | |
10 ** | |
11 ************************************************************************* | |
12 ** This is the header file for the generic hash-table implementation | |
13 ** used in SQLite. | |
14 */ | |
15 #ifndef _SQLITE_HASH_H_ | |
16 #define _SQLITE_HASH_H_ | |
17 | |
18 /* Forward declarations of structures. */ | |
19 typedef struct Hash Hash; | |
20 typedef struct HashElem HashElem; | |
21 | |
22 /* A complete hash table is an instance of the following structure. | |
23 ** The internals of this structure are intended to be opaque -- client | |
24 ** code should not attempt to access or modify the fields of this structure | |
25 ** directly. Change this structure only by using the routines below. | |
26 ** However, some of the "procedures" and "functions" for modifying and | |
27 ** accessing this structure are really macros, so we can't really make | |
28 ** this structure opaque. | |
29 ** | |
30 ** All elements of the hash table are on a single doubly-linked list. | |
31 ** Hash.first points to the head of this list. | |
32 ** | |
33 ** There are Hash.htsize buckets. Each bucket points to a spot in | |
34 ** the global doubly-linked list. The contents of the bucket are the | |
35 ** element pointed to plus the next _ht.count-1 elements in the list. | |
36 ** | |
37 ** Hash.htsize and Hash.ht may be zero. In that case lookup is done | |
38 ** by a linear search of the global list. For small tables, the | |
39 ** Hash.ht table is never allocated because if there are few elements | |
40 ** in the table, it is faster to do a linear search than to manage | |
41 ** the hash table. | |
42 */ | |
43 struct Hash { | |
44 unsigned int htsize; /* Number of buckets in the hash table */ | |
45 unsigned int count; /* Number of entries in this table */ | |
46 HashElem *first; /* The first element of the array */ | |
47 struct _ht { /* the hash table */ | |
48 int count; /* Number of entries with this hash */ | |
49 HashElem *chain; /* Pointer to first entry with this hash */ | |
50 } *ht; | |
51 }; | |
52 | |
53 /* Each element in the hash table is an instance of the following | |
54 ** structure. All elements are stored on a single doubly-linked list. | |
55 ** | |
56 ** Again, this structure is intended to be opaque, but it can't really | |
57 ** be opaque because it is used by macros. | |
58 */ | |
59 struct HashElem { | |
60 HashElem *next, *prev; /* Next and previous elements in the table */ | |
61 void *data; /* Data associated with this element */ | |
62 const char *pKey; /* Key associated with this element */ | |
63 }; | |
64 | |
65 /* | |
66 ** Access routines. To delete, insert a NULL pointer. | |
67 */ | |
68 void sqlite3HashInit(Hash*); | |
69 void *sqlite3HashInsert(Hash*, const char *pKey, void *pData); | |
70 void *sqlite3HashFind(const Hash*, const char *pKey); | |
71 void sqlite3HashClear(Hash*); | |
72 | |
73 /* | |
74 ** Macros for looping over all elements of a hash table. The idiom is | |
75 ** like this: | |
76 ** | |
77 ** Hash h; | |
78 ** HashElem *p; | |
79 ** ... | |
80 ** for(p=sqliteHashFirst(&h); p; p=sqliteHashNext(p)){ | |
81 ** SomeStructure *pData = sqliteHashData(p); | |
82 ** // do something with pData | |
83 ** } | |
84 */ | |
85 #define sqliteHashFirst(H) ((H)->first) | |
86 #define sqliteHashNext(E) ((E)->next) | |
87 #define sqliteHashData(E) ((E)->data) | |
88 /* #define sqliteHashKey(E) ((E)->pKey) // NOT USED */ | |
89 /* #define sqliteHashKeysize(E) ((E)->nKey) // NOT USED */ | |
90 | |
91 /* | |
92 ** Number of entries in a hash table | |
93 */ | |
94 /* #define sqliteHashCount(H) ((H)->count) // NOT USED */ | |
95 | |
96 #endif /* _SQLITE_HASH_H_ */ | |
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