| /* |
| ** 2001 September 22 |
| ** |
| ** The author disclaims copyright to this source code. In place of |
| ** a legal notice, here is a blessing: |
| ** |
| ** May you do good and not evil. |
| ** May you find forgiveness for yourself and forgive others. |
| ** May you share freely, never taking more than you give. |
| ** |
| ************************************************************************* |
| ** This is the implementation of generic hash-tables |
| ** used in SQLite. |
| */ |
| #include "sqliteInt.h" |
| #include <assert.h> |
| |
| /* Turn bulk memory into a hash table object by initializing the |
| ** fields of the Hash structure. |
| ** |
| ** "pNew" is a pointer to the hash table that is to be initialized. |
| */ |
| void sqlite3HashInit(Hash *pNew){ |
| assert( pNew!=0 ); |
| pNew->first = 0; |
| pNew->count = 0; |
| pNew->htsize = 0; |
| pNew->ht = 0; |
| } |
| |
| /* Remove all entries from a hash table. Reclaim all memory. |
| ** Call this routine to delete a hash table or to reset a hash table |
| ** to the empty state. |
| */ |
| void sqlite3HashClear(Hash *pH){ |
| HashElem *elem; /* For looping over all elements of the table */ |
| |
| assert( pH!=0 ); |
| elem = pH->first; |
| pH->first = 0; |
| sqlite3_free(pH->ht); |
| pH->ht = 0; |
| pH->htsize = 0; |
| while( elem ){ |
| HashElem *next_elem = elem->next; |
| sqlite3_free(elem); |
| elem = next_elem; |
| } |
| pH->count = 0; |
| } |
| |
| /* |
| ** The hashing function. |
| */ |
| static unsigned int strHash(const char *z, int nKey){ |
| int h = 0; |
| assert( nKey>=0 ); |
| while( nKey > 0 ){ |
| h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++]; |
| nKey--; |
| } |
| return h; |
| } |
| |
| |
| /* Link pNew element into the hash table pH. If pEntry!=0 then also |
| ** insert pNew into the pEntry hash bucket. |
| */ |
| static void insertElement( |
| Hash *pH, /* The complete hash table */ |
| struct _ht *pEntry, /* The entry into which pNew is inserted */ |
| HashElem *pNew /* The element to be inserted */ |
| ){ |
| HashElem *pHead; /* First element already in pEntry */ |
| if( pEntry ){ |
| pHead = pEntry->count ? pEntry->chain : 0; |
| pEntry->count++; |
| pEntry->chain = pNew; |
| }else{ |
| pHead = 0; |
| } |
| if( pHead ){ |
| pNew->next = pHead; |
| pNew->prev = pHead->prev; |
| if( pHead->prev ){ pHead->prev->next = pNew; } |
| else { pH->first = pNew; } |
| pHead->prev = pNew; |
| }else{ |
| pNew->next = pH->first; |
| if( pH->first ){ pH->first->prev = pNew; } |
| pNew->prev = 0; |
| pH->first = pNew; |
| } |
| } |
| |
| |
| /* Resize the hash table so that it cantains "new_size" buckets. |
| ** |
| ** The hash table might fail to resize if sqlite3_malloc() fails or |
| ** if the new size is the same as the prior size. |
| ** Return TRUE if the resize occurs and false if not. |
| */ |
| static int rehash(Hash *pH, unsigned int new_size){ |
| struct _ht *new_ht; /* The new hash table */ |
| HashElem *elem, *next_elem; /* For looping over existing elements */ |
| |
| #if SQLITE_MALLOC_SOFT_LIMIT>0 |
| if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){ |
| new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht); |
| } |
| if( new_size==pH->htsize ) return 0; |
| #endif |
| |
| /* The inability to allocates space for a larger hash table is |
| ** a performance hit but it is not a fatal error. So mark the |
| ** allocation as a benign. |
| */ |
| sqlite3BeginBenignMalloc(); |
| new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) ); |
| sqlite3EndBenignMalloc(); |
| |
| if( new_ht==0 ) return 0; |
| sqlite3_free(pH->ht); |
| pH->ht = new_ht; |
| pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht); |
| memset(new_ht, 0, new_size*sizeof(struct _ht)); |
| for(elem=pH->first, pH->first=0; elem; elem = next_elem){ |
| unsigned int h = strHash(elem->pKey, elem->nKey) % new_size; |
| next_elem = elem->next; |
| insertElement(pH, &new_ht[h], elem); |
| } |
| return 1; |
| } |
| |
| /* This function (for internal use only) locates an element in an |
| ** hash table that matches the given key. The hash for this key has |
| ** already been computed and is passed as the 4th parameter. |
| */ |
| static HashElem *findElementGivenHash( |
| const Hash *pH, /* The pH to be searched */ |
| const char *pKey, /* The key we are searching for */ |
| int nKey, /* Bytes in key (not counting zero terminator) */ |
| unsigned int h /* The hash for this key. */ |
| ){ |
| HashElem *elem; /* Used to loop thru the element list */ |
| int count; /* Number of elements left to test */ |
| |
| if( pH->ht ){ |
| struct _ht *pEntry = &pH->ht[h]; |
| elem = pEntry->chain; |
| count = pEntry->count; |
| }else{ |
| elem = pH->first; |
| count = pH->count; |
| } |
| while( count-- && ALWAYS(elem) ){ |
| if( elem->nKey==nKey && sqlite3StrNICmp(elem->pKey,pKey,nKey)==0 ){ |
| return elem; |
| } |
| elem = elem->next; |
| } |
| return 0; |
| } |
| |
| /* Remove a single entry from the hash table given a pointer to that |
| ** element and a hash on the element's key. |
| */ |
| static void removeElementGivenHash( |
| Hash *pH, /* The pH containing "elem" */ |
| HashElem* elem, /* The element to be removed from the pH */ |
| unsigned int h /* Hash value for the element */ |
| ){ |
| struct _ht *pEntry; |
| if( elem->prev ){ |
| elem->prev->next = elem->next; |
| }else{ |
| pH->first = elem->next; |
| } |
| if( elem->next ){ |
| elem->next->prev = elem->prev; |
| } |
| if( pH->ht ){ |
| pEntry = &pH->ht[h]; |
| if( pEntry->chain==elem ){ |
| pEntry->chain = elem->next; |
| } |
| pEntry->count--; |
| assert( pEntry->count>=0 ); |
| } |
| sqlite3_free( elem ); |
| pH->count--; |
| if( pH->count<=0 ){ |
| assert( pH->first==0 ); |
| assert( pH->count==0 ); |
| sqlite3HashClear(pH); |
| } |
| } |
| |
| /* Attempt to locate an element of the hash table pH with a key |
| ** that matches pKey,nKey. Return the data for this element if it is |
| ** found, or NULL if there is no match. |
| */ |
| void *sqlite3HashFind(const Hash *pH, const char *pKey, int nKey){ |
| HashElem *elem; /* The element that matches key */ |
| unsigned int h; /* A hash on key */ |
| |
| assert( pH!=0 ); |
| assert( pKey!=0 ); |
| assert( nKey>=0 ); |
| if( pH->ht ){ |
| h = strHash(pKey, nKey) % pH->htsize; |
| }else{ |
| h = 0; |
| } |
| elem = findElementGivenHash(pH, pKey, nKey, h); |
| return elem ? elem->data : 0; |
| } |
| |
| /* Insert an element into the hash table pH. The key is pKey,nKey |
| ** and the data is "data". |
| ** |
| ** If no element exists with a matching key, then a new |
| ** element is created and NULL is returned. |
| ** |
| ** If another element already exists with the same key, then the |
| ** new data replaces the old data and the old data is returned. |
| ** The key is not copied in this instance. If a malloc fails, then |
| ** the new data is returned and the hash table is unchanged. |
| ** |
| ** If the "data" parameter to this function is NULL, then the |
| ** element corresponding to "key" is removed from the hash table. |
| */ |
| void *sqlite3HashInsert(Hash *pH, const char *pKey, int nKey, void *data){ |
| unsigned int h; /* the hash of the key modulo hash table size */ |
| HashElem *elem; /* Used to loop thru the element list */ |
| HashElem *new_elem; /* New element added to the pH */ |
| |
| assert( pH!=0 ); |
| assert( pKey!=0 ); |
| assert( nKey>=0 ); |
| if( pH->htsize ){ |
| h = strHash(pKey, nKey) % pH->htsize; |
| }else{ |
| h = 0; |
| } |
| elem = findElementGivenHash(pH,pKey,nKey,h); |
| if( elem ){ |
| void *old_data = elem->data; |
| if( data==0 ){ |
| removeElementGivenHash(pH,elem,h); |
| }else{ |
| elem->data = data; |
| elem->pKey = pKey; |
| assert(nKey==elem->nKey); |
| } |
| return old_data; |
| } |
| if( data==0 ) return 0; |
| new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) ); |
| if( new_elem==0 ) return data; |
| new_elem->pKey = pKey; |
| new_elem->nKey = nKey; |
| new_elem->data = data; |
| pH->count++; |
| if( pH->count>=10 && pH->count > 2*pH->htsize ){ |
| if( rehash(pH, pH->count*2) ){ |
| assert( pH->htsize>0 ); |
| h = strHash(pKey, nKey) % pH->htsize; |
| } |
| } |
| if( pH->ht ){ |
| insertElement(pH, &pH->ht[h], new_elem); |
| }else{ |
| insertElement(pH, 0, new_elem); |
| } |
| return 0; |
| } |