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