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 implementation of generic hash-tables 13 ** used in SQLite. 14 */ 15 #include "sqliteInt.h" 16 #include <assert.h> 17 18 /* Turn bulk memory into a hash table object by initializing the 19 ** fields of the Hash structure. 20 ** 21 ** "pNew" is a pointer to the hash table that is to be initialized. 22 */ 23 void sqlite3HashInit(Hash *pNew){ 24 assert( pNew!=0 ); 25 pNew->first = 0; 26 pNew->count = 0; 27 pNew->htsize = 0; 28 pNew->ht = 0; 29 } 30 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. 34 */ 35 void sqlite3HashClear(Hash *pH){ 36 HashElem *elem; /* For looping over all elements of the table */ 37 38 assert( pH!=0 ); 39 elem = pH->first; 40 pH->first = 0; 41 sqlite3_free(pH->ht); 42 pH->ht = 0; 43 pH->htsize = 0; 44 while( elem ){ 45 HashElem *next_elem = elem->next; 46 sqlite3_free(elem); 47 elem = next_elem; 48 } 49 pH->count = 0; 50 } 51 52 /* 53 ** The hashing function. 54 */ 55 static unsigned int strHash(const char *z){ 56 unsigned int h = 0; 57 unsigned char c; 58 while( (c = (unsigned char)*z++)!=0 ){ /*OPTIMIZATION-IF-TRUE*/ 59 /* Knuth multiplicative hashing. (Sorting & Searching, p. 510). 60 ** 0x9e3779b1 is 2654435761 which is the closest prime number to 61 ** (2**32)*golden_ratio, where golden_ratio = (sqrt(5) - 1)/2. */ 62 h += sqlite3UpperToLower[c]; 63 h *= 0x9e3779b1; 64 } 65 return h; 66 } 67 68 69 /* Link pNew element into the hash table pH. If pEntry!=0 then also 70 ** insert pNew into the pEntry hash bucket. 71 */ 72 static void insertElement( 73 Hash *pH, /* The complete hash table */ 74 struct _ht *pEntry, /* The entry into which pNew is inserted */ 75 HashElem *pNew /* The element to be inserted */ 76 ){ 77 HashElem *pHead; /* First element already in pEntry */ 78 if( pEntry ){ 79 pHead = pEntry->count ? pEntry->chain : 0; 80 pEntry->count++; 81 pEntry->chain = pNew; 82 }else{ 83 pHead = 0; 84 } 85 if( pHead ){ 86 pNew->next = pHead; 87 pNew->prev = pHead->prev; 88 if( pHead->prev ){ pHead->prev->next = pNew; } 89 else { pH->first = pNew; } 90 pHead->prev = pNew; 91 }else{ 92 pNew->next = pH->first; 93 if( pH->first ){ pH->first->prev = pNew; } 94 pNew->prev = 0; 95 pH->first = pNew; 96 } 97 } 98 99 100 /* Resize the hash table so that it cantains "new_size" buckets. 101 ** 102 ** The hash table might fail to resize if sqlite3_malloc() fails or 103 ** if the new size is the same as the prior size. 104 ** Return TRUE if the resize occurs and false if not. 105 */ 106 static int rehash(Hash *pH, unsigned int new_size){ 107 struct _ht *new_ht; /* The new hash table */ 108 HashElem *elem, *next_elem; /* For looping over existing elements */ 109 110 #if SQLITE_MALLOC_SOFT_LIMIT>0 111 if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){ 112 new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht); 113 } 114 if( new_size==pH->htsize ) return 0; 115 #endif 116 117 /* The inability to allocates space for a larger hash table is 118 ** a performance hit but it is not a fatal error. So mark the 119 ** allocation as a benign. Use sqlite3Malloc()/memset(0) instead of 120 ** sqlite3MallocZero() to make the allocation, as sqlite3MallocZero() 121 ** only zeroes the requested number of bytes whereas this module will 122 ** use the actual amount of space allocated for the hash table (which 123 ** may be larger than the requested amount). 124 */ 125 sqlite3BeginBenignMalloc(); 126 new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) ); 127 sqlite3EndBenignMalloc(); 128 129 if( new_ht==0 ) return 0; 130 sqlite3_free(pH->ht); 131 pH->ht = new_ht; 132 pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht); 133 memset(new_ht, 0, new_size*sizeof(struct _ht)); 134 for(elem=pH->first, pH->first=0; elem; elem = next_elem){ 135 unsigned int h = strHash(elem->pKey) % new_size; 136 next_elem = elem->next; 137 insertElement(pH, &new_ht[h], elem); 138 } 139 return 1; 140 } 141 142 /* This function (for internal use only) locates an element in an 143 ** hash table that matches the given key. The hash for this key is 144 ** also computed and returned in the *pH parameter. 145 */ 146 static HashElem *findElementWithHash( 147 const Hash *pH, /* The pH to be searched */ 148 const char *pKey, /* The key we are searching for */ 149 unsigned int *pHash /* Write the hash value here */ 150 ){ 151 HashElem *elem; /* Used to loop thru the element list */ 152 int count; /* Number of elements left to test */ 153 unsigned int h; /* The computed hash */ 154 155 if( pH->ht ){ /*OPTIMIZATION-IF-TRUE*/ 156 struct _ht *pEntry; 157 h = strHash(pKey) % pH->htsize; 158 pEntry = &pH->ht[h]; 159 elem = pEntry->chain; 160 count = pEntry->count; 161 }else{ 162 h = 0; 163 elem = pH->first; 164 count = pH->count; 165 } 166 *pHash = h; 167 while( count-- ){ 168 assert( elem!=0 ); 169 if( sqlite3StrICmp(elem->pKey,pKey)==0 ){ 170 return elem; 171 } 172 elem = elem->next; 173 } 174 return 0; 175 } 176 177 /* Remove a single entry from the hash table given a pointer to that 178 ** element and a hash on the element's key. 179 */ 180 static void removeElementGivenHash( 181 Hash *pH, /* The pH containing "elem" */ 182 HashElem* elem, /* The element to be removed from the pH */ 183 unsigned int h /* Hash value for the element */ 184 ){ 185 struct _ht *pEntry; 186 if( elem->prev ){ 187 elem->prev->next = elem->next; 188 }else{ 189 pH->first = elem->next; 190 } 191 if( elem->next ){ 192 elem->next->prev = elem->prev; 193 } 194 if( pH->ht ){ 195 pEntry = &pH->ht[h]; 196 if( pEntry->chain==elem ){ 197 pEntry->chain = elem->next; 198 } 199 pEntry->count--; 200 assert( pEntry->count>=0 ); 201 } 202 sqlite3_free( elem ); 203 pH->count--; 204 if( pH->count==0 ){ 205 assert( pH->first==0 ); 206 assert( pH->count==0 ); 207 sqlite3HashClear(pH); 208 } 209 } 210 211 /* Attempt to locate an element of the hash table pH with a key 212 ** that matches pKey. Return the data for this element if it is 213 ** found, or NULL if there is no match. 214 */ 215 void *sqlite3HashFind(const Hash *pH, const char *pKey){ 216 HashElem *elem; /* The element that matches key */ 217 unsigned int h; /* A hash on key */ 218 219 assert( pH!=0 ); 220 assert( pKey!=0 ); 221 elem = findElementWithHash(pH, pKey, &h); 222 return elem ? elem->data : 0; 223 } 224 225 /* Insert an element into the hash table pH. The key is pKey 226 ** and the data is "data". 227 ** 228 ** If no element exists with a matching key, then a new 229 ** element is created and NULL is returned. 230 ** 231 ** If another element already exists with the same key, then the 232 ** new data replaces the old data and the old data is returned. 233 ** The key is not copied in this instance. If a malloc fails, then 234 ** the new data is returned and the hash table is unchanged. 235 ** 236 ** If the "data" parameter to this function is NULL, then the 237 ** element corresponding to "key" is removed from the hash table. 238 */ 239 void *sqlite3HashInsert(Hash *pH, const char *pKey, void *data){ 240 unsigned int h; /* the hash of the key modulo hash table size */ 241 HashElem *elem; /* Used to loop thru the element list */ 242 HashElem *new_elem; /* New element added to the pH */ 243 244 assert( pH!=0 ); 245 assert( pKey!=0 ); 246 elem = findElementWithHash(pH,pKey,&h); 247 if( elem ){ 248 void *old_data = elem->data; 249 if( data==0 ){ 250 removeElementGivenHash(pH,elem,h); 251 }else{ 252 elem->data = data; 253 elem->pKey = pKey; 254 } 255 return old_data; 256 } 257 if( data==0 ) return 0; 258 new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) ); 259 if( new_elem==0 ) return data; 260 new_elem->pKey = pKey; 261 new_elem->data = data; 262 pH->count++; 263 if( pH->count>=10 && pH->count > 2*pH->htsize ){ 264 if( rehash(pH, pH->count*2) ){ 265 assert( pH->htsize>0 ); 266 h = strHash(pKey) % pH->htsize; 267 } 268 } 269 insertElement(pH, pH->ht ? &pH->ht[h] : 0, new_elem); 270 return 0; 271 } 272