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Artifact 55b5fb474100cee0b901edaf203e26c970940f36:


     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 h = (h<<3) ^ h ^ sqlite3UpperToLower[c]; 60 } 61 return h; 62 }
63 64 65 /* Link pNew element into the hash table pH. If pEntry!=0 then also 66 ** insert pNew into the pEntry hash bucket. 67 */ 68 static void insertElement( 69 Hash *pH, /* The complete hash table */ 70 struct _ht *pEntry, /* The entry into which pNew is inserted */ 71 HashElem *pNew /* The element to be inserted */ 72 ){ 73 HashElem *pHead; /* First element already in pEntry */ 74 if( pEntry ){ 75 pHead = pEntry->count ? pEntry->chain : 0; 76 pEntry->count++; 77 pEntry->chain = pNew; 78 }else{ 79 pHead = 0; 80 } 81 if( pHead ){ 82 pNew->next = pHead; 83 pNew->prev = pHead->prev; 84 if( pHead->prev ){ pHead->prev->next = pNew; } 85 else { pH->first = pNew; } 86 pHead->prev = pNew; 87 }else{ 88 pNew->next = pH->first; 89 if( pH->first ){ pH->first->prev = pNew; } 90 pNew->prev = 0; 91 pH->first = pNew; 92 } 93 } 94 95 96 /* Resize the hash table so that it cantains "new_size" buckets. 97 ** 98 ** The hash table might fail to resize if sqlite3_malloc() fails or 99 ** if the new size is the same as the prior size. 100 ** Return TRUE if the resize occurs and false if not. 101 */ 102 static int rehash(Hash *pH, unsigned int new_size){ 103 struct _ht *new_ht; /* The new hash table */ 104 HashElem *elem, *next_elem; /* For looping over existing elements */ 105 106 #if SQLITE_MALLOC_SOFT_LIMIT>0 107 if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){ 108 new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht); 109 } 110 if( new_size==pH->htsize ) return 0; 111 #endif 112 113 /* The inability to allocates space for a larger hash table is 114 ** a performance hit but it is not a fatal error. So mark the 115 ** allocation as a benign. Use sqlite3Malloc()/memset(0) instead of 116 ** sqlite3MallocZero() to make the allocation, as sqlite3MallocZero() 117 ** only zeroes the requested number of bytes whereas this module will 118 ** use the actual amount of space allocated for the hash table (which 119 ** may be larger than the requested amount). 120 */ 121 sqlite3BeginBenignMalloc(); 122 new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) ); 123 sqlite3EndBenignMalloc(); 124 125 if( new_ht==0 ) return 0; 126 sqlite3_free(pH->ht); 127 pH->ht = new_ht; 128 pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht); 129 memset(new_ht, 0, new_size*sizeof(struct _ht)); 130 for(elem=pH->first, pH->first=0; elem; elem = next_elem){ 131 unsigned int h = strHash(elem->pKey) % new_size; 132 next_elem = elem->next; 133 insertElement(pH, &new_ht[h], elem); 134 } 135 return 1; 136 } 137 138 /* This function (for internal use only) locates an element in an 139 ** hash table that matches the given key. The hash for this key is 140 ** also computed and returned in the *pH parameter. 141 */ 142 static HashElem *findElementWithHash( 143 const Hash *pH, /* The pH to be searched */ 144 const char *pKey, /* The key we are searching for */ 145 unsigned int *pHash /* Write the hash value here */ 146 ){ 147 HashElem *elem; /* Used to loop thru the element list */ 148 int count; /* Number of elements left to test */ 149 unsigned int h; /* The computed hash */ 150 151 if( pH->ht ){ /*OPTIMIZATION-IF-TRUE*/ 152 struct _ht *pEntry; 153 h = strHash(pKey) % pH->htsize; 154 pEntry = &pH->ht[h]; 155 elem = pEntry->chain; 156 count = pEntry->count; 157 }else{ 158 h = 0; 159 elem = pH->first; 160 count = pH->count; 161 } 162 *pHash = h; 163 while( count-- ){ 164 assert( elem!=0 ); 165 if( sqlite3StrICmp(elem->pKey,pKey)==0 ){ 166 return elem; 167 } 168 elem = elem->next; 169 } 170 return 0; 171 } 172 173 /* Remove a single entry from the hash table given a pointer to that 174 ** element and a hash on the element's key. 175 */ 176 static void removeElementGivenHash( 177 Hash *pH, /* The pH containing "elem" */ 178 HashElem* elem, /* The element to be removed from the pH */ 179 unsigned int h /* Hash value for the element */ 180 ){ 181 struct _ht *pEntry; 182 if( elem->prev ){ 183 elem->prev->next = elem->next; 184 }else{ 185 pH->first = elem->next; 186 } 187 if( elem->next ){ 188 elem->next->prev = elem->prev; 189 } 190 if( pH->ht ){ 191 pEntry = &pH->ht[h]; 192 if( pEntry->chain==elem ){ 193 pEntry->chain = elem->next; 194 } 195 pEntry->count--; 196 assert( pEntry->count>=0 ); 197 } 198 sqlite3_free( elem ); 199 pH->count--; 200 if( pH->count==0 ){ 201 assert( pH->first==0 ); 202 assert( pH->count==0 ); 203 sqlite3HashClear(pH); 204 } 205 } 206 207 /* Attempt to locate an element of the hash table pH with a key 208 ** that matches pKey. Return the data for this element if it is 209 ** found, or NULL if there is no match. 210 */ 211 void *sqlite3HashFind(const Hash *pH, const char *pKey){ 212 HashElem *elem; /* The element that matches key */ 213 unsigned int h; /* A hash on key */ 214 215 assert( pH!=0 ); 216 assert( pKey!=0 ); 217 elem = findElementWithHash(pH, pKey, &h); 218 return elem ? elem->data : 0; 219 } 220 221 /* Insert an element into the hash table pH. The key is pKey 222 ** and the data is "data". 223 ** 224 ** If no element exists with a matching key, then a new 225 ** element is created and NULL is returned. 226 ** 227 ** If another element already exists with the same key, then the 228 ** new data replaces the old data and the old data is returned. 229 ** The key is not copied in this instance. If a malloc fails, then 230 ** the new data is returned and the hash table is unchanged. 231 ** 232 ** If the "data" parameter to this function is NULL, then the 233 ** element corresponding to "key" is removed from the hash table. 234 */ 235 void *sqlite3HashInsert(Hash *pH, const char *pKey, void *data){ 236 unsigned int h; /* the hash of the key modulo hash table size */ 237 HashElem *elem; /* Used to loop thru the element list */ 238 HashElem *new_elem; /* New element added to the pH */ 239 240 assert( pH!=0 ); 241 assert( pKey!=0 ); 242 elem = findElementWithHash(pH,pKey,&h); 243 if( elem ){ 244 void *old_data = elem->data; 245 if( data==0 ){ 246 removeElementGivenHash(pH,elem,h); 247 }else{ 248 elem->data = data; 249 elem->pKey = pKey; 250 } 251 return old_data; 252 } 253 if( data==0 ) return 0; 254 new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) ); 255 if( new_elem==0 ) return data; 256 new_elem->pKey = pKey; 257 new_elem->data = data; 258 pH->count++; 259 if( pH->count>=10 && pH->count > 2*pH->htsize ){ 260 if( rehash(pH, pH->count*2) ){ 261 assert( pH->htsize>0 ); 262 h = strHash(pKey) % pH->htsize; 263 } 264 } 265 insertElement(pH, pH->ht ? &pH->ht[h] : 0, new_elem); 266 return 0; 267 }