4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
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 implementation of generic hash-tables
15 #include "sqliteInt.h"
18 /* Turn bulk memory into a hash table object by initializing the
19 ** fields of the Hash structure.
21 ** "pNew" is a pointer to the hash table that is to be initialized.
23 void sqlite3HashInit(Hash *pNew){
31 /* Remove all entries from a hash table. Reclaim all memory.
32 ** Call this routine to delete a hash table or to reset a hash table
33 ** to the empty state.
35 void sqlite3HashClear(Hash *pH){
36 HashElem *elem; /* For looping over all elements of the table */
45 HashElem *next_elem = elem->next;
53 ** The hashing function.
55 static unsigned int strHash(const char *z, int nKey){
59 h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++];
66 /* Link pNew element into the hash table pH. If pEntry!=0 then also
67 ** insert pNew into the pEntry hash bucket.
69 static void insertElement(
70 Hash *pH, /* The complete hash table */
71 struct _ht *pEntry, /* The entry into which pNew is inserted */
72 HashElem *pNew /* The element to be inserted */
74 HashElem *pHead; /* First element already in pEntry */
76 pHead = pEntry->count ? pEntry->chain : 0;
84 pNew->prev = pHead->prev;
85 if( pHead->prev ){ pHead->prev->next = pNew; }
86 else { pH->first = pNew; }
89 pNew->next = pH->first;
90 if( pH->first ){ pH->first->prev = pNew; }
97 /* Resize the hash table so that it cantains "new_size" buckets.
99 ** The hash table might fail to resize if sqlite3_malloc() fails or
100 ** if the new size is the same as the prior size.
101 ** Return TRUE if the resize occurs and false if not.
103 static int rehash(Hash *pH, unsigned int new_size){
104 struct _ht *new_ht; /* The new hash table */
105 HashElem *elem, *next_elem; /* For looping over existing elements */
107 #if SQLITE_MALLOC_SOFT_LIMIT>0
108 if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){
109 new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht);
111 if( new_size==pH->htsize ) return 0;
114 /* The inability to allocates space for a larger hash table is
115 ** a performance hit but it is not a fatal error. So mark the
116 ** allocation as a benign.
118 sqlite3BeginBenignMalloc();
119 new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );
120 sqlite3EndBenignMalloc();
122 if( new_ht==0 ) return 0;
123 sqlite3_free(pH->ht);
125 pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht);
126 memset(new_ht, 0, new_size*sizeof(struct _ht));
127 for(elem=pH->first, pH->first=0; elem; elem = next_elem){
128 unsigned int h = strHash(elem->pKey, elem->nKey) % new_size;
129 next_elem = elem->next;
130 insertElement(pH, &new_ht[h], elem);
135 /* This function (for internal use only) locates an element in an
136 ** hash table that matches the given key. The hash for this key has
137 ** already been computed and is passed as the 4th parameter.
139 static HashElem *findElementGivenHash(
140 const Hash *pH, /* The pH to be searched */
141 const char *pKey, /* The key we are searching for */
142 int nKey, /* Bytes in key (not counting zero terminator) */
143 unsigned int h /* The hash for this key. */
145 HashElem *elem; /* Used to loop thru the element list */
146 int count; /* Number of elements left to test */
149 struct _ht *pEntry = &pH->ht[h];
150 elem = pEntry->chain;
151 count = pEntry->count;
156 while( count-- && ALWAYS(elem) ){
157 if( elem->nKey==nKey && sqlite3StrNICmp(elem->pKey,pKey,nKey)==0 ){
165 /* Remove a single entry from the hash table given a pointer to that
166 ** element and a hash on the element's key.
168 static void removeElementGivenHash(
169 Hash *pH, /* The pH containing "elem" */
170 HashElem* elem, /* The element to be removed from the pH */
171 unsigned int h /* Hash value for the element */
175 elem->prev->next = elem->next;
177 pH->first = elem->next;
180 elem->next->prev = elem->prev;
184 if( pEntry->chain==elem ){
185 pEntry->chain = elem->next;
188 assert( pEntry->count>=0 );
190 sqlite3_free( elem );
193 assert( pH->first==0 );
194 assert( pH->count==0 );
195 sqlite3HashClear(pH);
199 /* Attempt to locate an element of the hash table pH with a key
200 ** that matches pKey,nKey. Return the data for this element if it is
201 ** found, or NULL if there is no match.
203 void *sqlite3HashFind(const Hash *pH, const char *pKey, int nKey){
204 HashElem *elem; /* The element that matches key */
205 unsigned int h; /* A hash on key */
211 h = strHash(pKey, nKey) % pH->htsize;
215 elem = findElementGivenHash(pH, pKey, nKey, h);
216 return elem ? elem->data : 0;
219 /* Insert an element into the hash table pH. The key is pKey,nKey
220 ** and the data is "data".
222 ** If no element exists with a matching key, then a new
223 ** element is created and NULL is returned.
225 ** If another element already exists with the same key, then the
226 ** new data replaces the old data and the old data is returned.
227 ** The key is not copied in this instance. If a malloc fails, then
228 ** the new data is returned and the hash table is unchanged.
230 ** If the "data" parameter to this function is NULL, then the
231 ** element corresponding to "key" is removed from the hash table.
233 void *sqlite3HashInsert(Hash *pH, const char *pKey, int nKey, void *data){
234 unsigned int h; /* the hash of the key modulo hash table size */
235 HashElem *elem; /* Used to loop thru the element list */
236 HashElem *new_elem; /* New element added to the pH */
242 h = strHash(pKey, nKey) % pH->htsize;
246 elem = findElementGivenHash(pH,pKey,nKey,h);
248 void *old_data = elem->data;
250 removeElementGivenHash(pH,elem,h);
254 assert(nKey==elem->nKey);
258 if( data==0 ) return 0;
259 new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );
260 if( new_elem==0 ) return data;
261 new_elem->pKey = pKey;
262 new_elem->nKey = nKey;
263 new_elem->data = data;
265 if( pH->count>=10 && pH->count > 2*pH->htsize ){
266 if( rehash(pH, pH->count*2) ){
267 assert( pH->htsize>0 );
268 h = strHash(pKey, nKey) % pH->htsize;
272 insertElement(pH, &pH->ht[h], new_elem);
274 insertElement(pH, 0, new_elem);