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 ** $Id: hash.c,v 1.11 2004/01/08 02:17:33 drh Exp $ 16 */ 17 #include "sqliteInt.h" 18 #include <assert.h> 19 20 /* Turn bulk memory into a hash table object by initializing the 21 ** fields of the Hash structure. 22 ** 23 ** "new" is a pointer to the hash table that is to be initialized. 24 ** keyClass is one of the constants SQLITE_HASH_INT, SQLITE_HASH_POINTER, 25 ** SQLITE_HASH_BINARY, or SQLITE_HASH_STRING. The value of keyClass 26 ** determines what kind of key the hash table will use. "copyKey" is 27 ** true if the hash table should make its own private copy of keys and 28 ** false if it should just use the supplied pointer. CopyKey only makes 29 ** sense for SQLITE_HASH_STRING and SQLITE_HASH_BINARY and is ignored 30 ** for other key classes. 31 */ 32 void sqliteHashInit(Hash *new, int keyClass, int copyKey){ 33 assert( new!=0 ); 34 assert( keyClass>=SQLITE_HASH_INT && keyClass<=SQLITE_HASH_BINARY ); 35 new->keyClass = keyClass; 36 new->copyKey = copyKey && 37 (keyClass==SQLITE_HASH_STRING || keyClass==SQLITE_HASH_BINARY); 38 new->first = 0; 39 new->count = 0; 40 new->htsize = 0; 41 new->ht = 0; 42 } 43 44 /* Remove all entries from a hash table. Reclaim all memory. 45 ** Call this routine to delete a hash table or to reset a hash table 46 ** to the empty state. 47 */ 48 void sqliteHashClear(Hash *pH){ 49 HashElem *elem; /* For looping over all elements of the table */ 50 51 assert( pH!=0 ); 52 elem = pH->first; 53 pH->first = 0; 54 if( pH->ht ) sqliteFree(pH->ht); 55 pH->ht = 0; 56 pH->htsize = 0; 57 while( elem ){ 58 HashElem *next_elem = elem->next; 59 if( pH->copyKey && elem->pKey ){ 60 sqliteFree(elem->pKey); 61 } 62 sqliteFree(elem); 63 elem = next_elem; 64 } 65 pH->count = 0; 66 } 67 68 /* 69 ** Hash and comparison functions when the mode is SQLITE_HASH_INT 70 */ 71 static int intHash(const void *pKey, int nKey){ 72 return nKey ^ (nKey<<8) ^ (nKey>>8); 73 } 74 static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){ 75 return n2 - n1; 76 } 77 78 #if 0 /* NOT USED */ 79 /* 80 ** Hash and comparison functions when the mode is SQLITE_HASH_POINTER 81 */ 82 static int ptrHash(const void *pKey, int nKey){ 83 uptr x = Addr(pKey); 84 return x ^ (x<<8) ^ (x>>8); 85 } 86 static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){ 87 if( pKey1==pKey2 ) return 0; 88 if( pKey1<pKey2 ) return -1; 89 return 1; 90 } 91 #endif 92 93 /* 94 ** Hash and comparison functions when the mode is SQLITE_HASH_STRING 95 */ 96 static int strHash(const void *pKey, int nKey){ 97 return sqliteHashNoCase((const char*)pKey, nKey); 98 } 99 static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){ 100 if( n1!=n2 ) return n2-n1; 101 return sqliteStrNICmp((const char*)pKey1,(const char*)pKey2,n1); 102 } 103 104 /* 105 ** Hash and comparison functions when the mode is SQLITE_HASH_BINARY 106 */ 107 static int binHash(const void *pKey, int nKey){ 108 int h = 0; 109 const char *z = (const char *)pKey; 110 while( nKey-- > 0 ){ 111 h = (h<<3) ^ h ^ *(z++); 112 } 113 return h & 0x7fffffff; 114 } 115 static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){ 116 if( n1!=n2 ) return n2-n1; 117 return memcmp(pKey1,pKey2,n1); 118 } 119 120 /* 121 ** Return a pointer to the appropriate hash function given the key class. 122 ** 123 ** The C syntax in this function definition may be unfamilar to some 124 ** programmers, so we provide the following additional explanation: 125 ** 126 ** The name of the function is "hashFunction". The function takes a 127 ** single parameter "keyClass". The return value of hashFunction() 128 ** is a pointer to another function. Specifically, the return value 129 ** of hashFunction() is a pointer to a function that takes two parameters 130 ** with types "const void*" and "int" and returns an "int". 131 */ 132 static int (*hashFunction(int keyClass))(const void*,int){ 133 switch( keyClass ){ 134 case SQLITE_HASH_INT: return &intHash; 135 /* case SQLITE_HASH_POINTER: return &ptrHash; // NOT USED */ 136 case SQLITE_HASH_STRING: return &strHash; 137 case SQLITE_HASH_BINARY: return &binHash;; 138 default: break; 139 } 140 return 0; 141 } 142 143 /* 144 ** Return a pointer to the appropriate hash function given the key class. 145 ** 146 ** For help in interpreted the obscure C code in the function definition, 147 ** see the header comment on the previous function. 148 */ 149 static int (*compareFunction(int keyClass))(const void*,int,const void*,int){ 150 switch( keyClass ){ 151 case SQLITE_HASH_INT: return &intCompare; 152 /* case SQLITE_HASH_POINTER: return &ptrCompare; // NOT USED */ 153 case SQLITE_HASH_STRING: return &strCompare; 154 case SQLITE_HASH_BINARY: return &binCompare; 155 default: break; 156 } 157 return 0; 158 } 159 160 161 /* Resize the hash table so that it cantains "new_size" buckets. 162 ** "new_size" must be a power of 2. The hash table might fail 163 ** to resize if sqliteMalloc() fails. 164 */ 165 static void rehash(Hash *pH, int new_size){ 166 struct _ht *new_ht; /* The new hash table */ 167 HashElem *elem, *next_elem; /* For looping over existing elements */ 168 HashElem *x; /* Element being copied to new hash table */ 169 int (*xHash)(const void*,int); /* The hash function */ 170 171 assert( (new_size & (new_size-1))==0 ); 172 new_ht = (struct _ht *)sqliteMalloc( new_size*sizeof(struct _ht) ); 173 if( new_ht==0 ) return; 174 if( pH->ht ) sqliteFree(pH->ht); 175 pH->ht = new_ht; 176 pH->htsize = new_size; 177 xHash = hashFunction(pH->keyClass); 178 for(elem=pH->first, pH->first=0; elem; elem = next_elem){ 179 int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1); 180 next_elem = elem->next; 181 x = new_ht[h].chain; 182 if( x ){ 183 elem->next = x; 184 elem->prev = x->prev; 185 if( x->prev ) x->prev->next = elem; 186 else pH->first = elem; 187 x->prev = elem; 188 }else{ 189 elem->next = pH->first; 190 if( pH->first ) pH->first->prev = elem; 191 elem->prev = 0; 192 pH->first = elem; 193 } 194 new_ht[h].chain = elem; 195 new_ht[h].count++; 196 } 197 } 198 199 /* This function (for internal use only) locates an element in an 200 ** hash table that matches the given key. The hash for this key has 201 ** already been computed and is passed as the 4th parameter. 202 */ 203 static HashElem *findElementGivenHash( 204 const Hash *pH, /* The pH to be searched */ 205 const void *pKey, /* The key we are searching for */ 206 int nKey, 207 int h /* The hash for this key. */ 208 ){ 209 HashElem *elem; /* Used to loop thru the element list */ 210 int count; /* Number of elements left to test */ 211 int (*xCompare)(const void*,int,const void*,int); /* comparison function */ 212 213 if( pH->ht ){ 214 elem = pH->ht[h].chain; 215 count = pH->ht[h].count; 216 xCompare = compareFunction(pH->keyClass); 217 while( count-- && elem ){ 218 if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){ 219 return elem; 220 } 221 elem = elem->next; 222 } 223 } 224 return 0; 225 } 226 227 /* Remove a single entry from the hash table given a pointer to that 228 ** element and a hash on the element's key. 229 */ 230 static void removeElementGivenHash( 231 Hash *pH, /* The pH containing "elem" */ 232 HashElem* elem, /* The element to be removed from the pH */ 233 int h /* Hash value for the element */ 234 ){ 235 if( elem->prev ){ 236 elem->prev->next = elem->next; 237 }else{ 238 pH->first = elem->next; 239 } 240 if( elem->next ){ 241 elem->next->prev = elem->prev; 242 } 243 if( pH->ht[h].chain==elem ){ 244 pH->ht[h].chain = elem->next; 245 } 246 pH->ht[h].count--; 247 if( pH->ht[h].count<=0 ){ 248 pH->ht[h].chain = 0; 249 } 250 if( pH->copyKey && elem->pKey ){ 251 sqliteFree(elem->pKey); 252 } 253 sqliteFree( elem ); 254 pH->count--; 255 } 256 257 /* Attempt to locate an element of the hash table pH with a key 258 ** that matches pKey,nKey. Return the data for this element if it is 259 ** found, or NULL if there is no match. 260 */ 261 void *sqliteHashFind(const Hash *pH, const void *pKey, int nKey){ 262 int h; /* A hash on key */ 263 HashElem *elem; /* The element that matches key */ 264 int (*xHash)(const void*,int); /* The hash function */ 265 266 if( pH==0 || pH->ht==0 ) return 0; 267 xHash = hashFunction(pH->keyClass); 268 assert( xHash!=0 ); 269 h = (*xHash)(pKey,nKey); 270 assert( (pH->htsize & (pH->htsize-1))==0 ); 271 elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1)); 272 return elem ? elem->data : 0; 273 } 274 275 /* Insert an element into the hash table pH. The key is pKey,nKey 276 ** and the data is "data". 277 ** 278 ** If no element exists with a matching key, then a new 279 ** element is created. A copy of the key is made if the copyKey 280 ** flag is set. NULL is returned. 281 ** 282 ** If another element already exists with the same key, then the 283 ** new data replaces the old data and the old data is returned. 284 ** The key is not copied in this instance. If a malloc fails, then 285 ** the new data is returned and the hash table is unchanged. 286 ** 287 ** If the "data" parameter to this function is NULL, then the 288 ** element corresponding to "key" is removed from the hash table. 289 */ 290 void *sqliteHashInsert(Hash *pH, const void *pKey, int nKey, void *data){ 291 int hraw; /* Raw hash value of the key */ 292 int h; /* the hash of the key modulo hash table size */ 293 HashElem *elem; /* Used to loop thru the element list */ 294 HashElem *new_elem; /* New element added to the pH */ 295 int (*xHash)(const void*,int); /* The hash function */ 296 297 assert( pH!=0 ); 298 xHash = hashFunction(pH->keyClass); 299 assert( xHash!=0 ); 300 hraw = (*xHash)(pKey, nKey); 301 assert( (pH->htsize & (pH->htsize-1))==0 ); 302 h = hraw & (pH->htsize-1); 303 elem = findElementGivenHash(pH,pKey,nKey,h); 304 if( elem ){ 305 void *old_data = elem->data; 306 if( data==0 ){ 307 removeElementGivenHash(pH,elem,h); 308 }else{ 309 elem->data = data; 310 } 311 return old_data; 312 } 313 if( data==0 ) return 0; 314 new_elem = (HashElem*)sqliteMalloc( sizeof(HashElem) ); 315 if( new_elem==0 ) return data; 316 if( pH->copyKey && pKey!=0 ){ 317 new_elem->pKey = sqliteMallocRaw( nKey ); 318 if( new_elem->pKey==0 ){ 319 sqliteFree(new_elem); 320 return data; 321 } 322 memcpy((void*)new_elem->pKey, pKey, nKey); 323 }else{ 324 new_elem->pKey = (void*)pKey; 325 } 326 new_elem->nKey = nKey; 327 pH->count++; 328 if( pH->htsize==0 ) rehash(pH,8); 329 if( pH->htsize==0 ){ 330 pH->count = 0; 331 sqliteFree(new_elem); 332 return data; 333 } 334 if( pH->count > pH->htsize ){ 335 rehash(pH,pH->htsize*2); 336 } 337 assert( (pH->htsize & (pH->htsize-1))==0 ); 338 h = hraw & (pH->htsize-1); 339 elem = pH->ht[h].chain; 340 if( elem ){ 341 new_elem->next = elem; 342 new_elem->prev = elem->prev; 343 if( elem->prev ){ elem->prev->next = new_elem; } 344 else { pH->first = new_elem; } 345 elem->prev = new_elem; 346 }else{ 347 new_elem->next = pH->first; 348 new_elem->prev = 0; 349 if( pH->first ){ pH->first->prev = new_elem; } 350 pH->first = new_elem; 351 } 352 pH->ht[h].count++; 353 pH->ht[h].chain = new_elem; 354 new_elem->data = data; 355 return 0; 356 } 357