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 | unsigned 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) |
95 | |
96 | #endif /* SQLITE_HASH_H */ |
97 | |