Merge sqlite-release(3.40.1) into prerelease-integration
[sqlcipher.git] / src / hash.h
blob3f491e45c04245614f0f91ddcc751c490c7f951e
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.
11 *************************************************************************
12 ** This is the header file for the generic hash-table implementation
13 ** used in SQLite.
15 #ifndef SQLITE_HASH_H
16 #define SQLITE_HASH_H
18 /* Forward declarations of structures. */
19 typedef struct Hash Hash;
20 typedef struct HashElem HashElem;
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.
30 ** All elements of the hash table are on a single doubly-linked list.
31 ** Hash.first points to the head of this list.
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.
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.
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;
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.
56 ** Again, this structure is intended to be opaque, but it can't really
57 ** be opaque because it is used by macros.
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 */
66 ** Access routines. To delete, insert a NULL pointer.
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*);
74 ** Macros for looping over all elements of a hash table. The idiom is
75 ** like this:
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 ** }
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 */
92 ** Number of entries in a hash table
94 #define sqliteHashCount(H) ((H)->count)
96 #endif /* SQLITE_HASH_H */