ext/fts2/fts2_hash.c

   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 used in SQLite.
  13 ** We've modified it slightly to serve as a standalone hash table
  14 ** implementation for the full-text indexing module.
  15 */
  16
  17 /*
  18 ** The code in this file is only compiled if:
  19 **
  20 **     * The FTS2 module is being built as an extension
  21 **       (in which case SQLITE_CORE is not defined), or
  22 **
  23 **     * The FTS2 module is being built into the core of
  24 **       SQLite (in which case SQLITE_ENABLE_FTS2 is defined).
  25 */
  26 #if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2)
  27
  28 #include <assert.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31
  32 #include "sqlite3.h"
  33 #include "sqlite3ext.h"
  34 SQLITE_EXTENSION_INIT3
  35 #include "fts2_hash.h"
  36
  37 /*
  38 ** Malloc and Free functions
  39 */
  40 static void *fts2HashMalloc(int n){
  41   void *p = sqlite3_malloc(n);
  42   if( p ){
  43     memset(p, 0, n);
  44   }
  45   return p;
  46 }
  47 static void fts2HashFree(void *p){
  48   sqlite3_free(p);
  49 }
  50
  51 /* Turn bulk memory into a hash table object by initializing the
  52 ** fields of the Hash structure.
  53 **
  54 ** "pNew" is a pointer to the hash table that is to be initialized.
  55 ** keyClass is one of the constants
  56 ** FTS2_HASH_BINARY or FTS2_HASH_STRING.  The value of keyClass
  57 ** determines what kind of key the hash table will use.  "copyKey" is
  58 ** true if the hash table should make its own private copy of keys and
  59 ** false if it should just use the supplied pointer.
  60 */
  61 void sqlite3Fts2HashInit(fts2Hash *pNew, int keyClass, int copyKey){
  62   assert( pNew!=0 );
  63   assert( keyClass>=FTS2_HASH_STRING && keyClass<=FTS2_HASH_BINARY );
  64   pNew->keyClass = keyClass;
  65   pNew->copyKey = copyKey;
  66   pNew->first = 0;
  67   pNew->count = 0;
  68   pNew->htsize = 0;
  69   pNew->ht = 0;
  70 }
  71
  72 /* Remove all entries from a hash table.  Reclaim all memory.
  73 ** Call this routine to delete a hash table or to reset a hash table
  74 ** to the empty state.
  75 */
  76 void sqlite3Fts2HashClear(fts2Hash *pH){
  77   fts2HashElem *elem;         /* For looping over all elements of the table */
  78
  79   assert( pH!=0 );
  80   elem = pH->first;
  81   pH->first = 0;
  82   fts2HashFree(pH->ht);
  83   pH->ht = 0;
  84   pH->htsize = 0;
  85   while( elem ){
  86     fts2HashElem *next_elem = elem->next;
  87     if( pH->copyKey && elem->pKey ){
  88       fts2HashFree(elem->pKey);
  89     }
  90     fts2HashFree(elem);
  91     elem = next_elem;
  92   }
  93   pH->count = 0;
  94 }
  95
  96 /*
  97 ** Hash and comparison functions when the mode is FTS2_HASH_STRING
  98 */
  99 static int strHash(const void *pKey, int nKey){
 100   const char *z = (const char *)pKey;
 101   int h = 0;
 102   if( nKey<=0 ) nKey = (int) strlen(z);
 103   while( nKey > 0  ){
 104     h = (h<<3) ^ h ^ *z++;
 105     nKey--;
 106   }
 107   return h & 0x7fffffff;
 108 }
 109 static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
 110   if( n1!=n2 ) return 1;
 111   return strncmp((const char*)pKey1,(const char*)pKey2,n1);
 112 }
 113
 114 /*
 115 ** Hash and comparison functions when the mode is FTS2_HASH_BINARY
 116 */
 117 static int binHash(const void *pKey, int nKey){
 118   int h = 0;
 119   const char *z = (const char *)pKey;
 120   while( nKey-- > 0 ){
 121     h = (h<<3) ^ h ^ *(z++);
 122   }
 123   return h & 0x7fffffff;
 124 }
 125 static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
 126   if( n1!=n2 ) return 1;
 127   return memcmp(pKey1,pKey2,n1);
 128 }
 129
 130 /*
 131 ** Return a pointer to the appropriate hash function given the key class.
 132 **
 133 ** The C syntax in this function definition may be unfamilar to some
 134 ** programmers, so we provide the following additional explanation:
 135 **
 136 ** The name of the function is "hashFunction".  The function takes a
 137 ** single parameter "keyClass".  The return value of hashFunction()
 138 ** is a pointer to another function.  Specifically, the return value
 139 ** of hashFunction() is a pointer to a function that takes two parameters
 140 ** with types "const void*" and "int" and returns an "int".
 141 */
 142 static int (*hashFunction(int keyClass))(const void*,int){
 143   if( keyClass==FTS2_HASH_STRING ){
 144     return &strHash;
 145   }else{
 146     assert( keyClass==FTS2_HASH_BINARY );
 147     return &binHash;
 148   }
 149 }
 150
 151 /*
 152 ** Return a pointer to the appropriate hash function given the key class.
 153 **
 154 ** For help in interpreted the obscure C code in the function definition,
 155 ** see the header comment on the previous function.
 156 */
 157 static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
 158   if( keyClass==FTS2_HASH_STRING ){
 159     return &strCompare;
 160   }else{
 161     assert( keyClass==FTS2_HASH_BINARY );
 162     return &binCompare;
 163   }
 164 }
 165
 166 /* Link an element into the hash table
 167 */
 168 static void insertElement(
 169   fts2Hash *pH,            /* The complete hash table */
 170   struct _fts2ht *pEntry,  /* The entry into which pNew is inserted */
 171   fts2HashElem *pNew       /* The element to be inserted */
 172 ){
 173   fts2HashElem *pHead;     /* First element already in pEntry */
 174   pHead = pEntry->chain;
 175   if( pHead ){
 176     pNew->next = pHead;
 177     pNew->prev = pHead->prev;
 178     if( pHead->prev ){ pHead->prev->next = pNew; }
 179     else             { pH->first = pNew; }
 180     pHead->prev = pNew;
 181   }else{
 182     pNew->next = pH->first;
 183     if( pH->first ){ pH->first->prev = pNew; }
 184     pNew->prev = 0;
 185     pH->first = pNew;
 186   }
 187   pEntry->count++;
 188   pEntry->chain = pNew;
 189 }
 190
 191
 192 /* Resize the hash table so that it cantains "new_size" buckets.
 193 ** "new_size" must be a power of 2.  The hash table might fail
 194 ** to resize if sqliteMalloc() fails.
 195 */
 196 static void rehash(fts2Hash *pH, int new_size){
 197   struct _fts2ht *new_ht;          /* The new hash table */
 198   fts2HashElem *elem, *next_elem;  /* For looping over existing elements */
 199   int (*xHash)(const void*,int);   /* The hash function */
 200
 201   assert( (new_size & (new_size-1))==0 );
 202   new_ht = (struct _fts2ht *)fts2HashMalloc( new_size*sizeof(struct _fts2ht) );
 203   if( new_ht==0 ) return;
 204   fts2HashFree(pH->ht);
 205   pH->ht = new_ht;
 206   pH->htsize = new_size;
 207   xHash = hashFunction(pH->keyClass);
 208   for(elem=pH->first, pH->first=0; elem; elem = next_elem){
 209     int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
 210     next_elem = elem->next;
 211     insertElement(pH, &new_ht[h], elem);
 212   }
 213 }
 214
 215 /* This function (for internal use only) locates an element in an
 216 ** hash table that matches the given key.  The hash for this key has
 217 ** already been computed and is passed as the 4th parameter.
 218 */
 219 static fts2HashElem *findElementGivenHash(
 220   const fts2Hash *pH, /* The pH to be searched */
 221   const void *pKey,   /* The key we are searching for */
 222   int nKey,
 223   int h               /* The hash for this key. */
 224 ){
 225   fts2HashElem *elem;            /* Used to loop thru the element list */
 226   int count;                     /* Number of elements left to test */
 227   int (*xCompare)(const void*,int,const void*,int);  /* comparison function */
 228
 229   if( pH->ht ){
 230     struct _fts2ht *pEntry = &pH->ht[h];
 231     elem = pEntry->chain;
 232     count = pEntry->count;
 233     xCompare = compareFunction(pH->keyClass);
 234     while( count-- && elem ){
 235       if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){
 236         return elem;
 237       }
 238       elem = elem->next;
 239     }
 240   }
 241   return 0;
 242 }
 243
 244 /* Remove a single entry from the hash table given a pointer to that
 245 ** element and a hash on the element's key.
 246 */
 247 static void removeElementGivenHash(
 248   fts2Hash *pH,         /* The pH containing "elem" */
 249   fts2HashElem* elem,   /* The element to be removed from the pH */
 250   int h                 /* Hash value for the element */
 251 ){
 252   struct _fts2ht *pEntry;
 253   if( elem->prev ){
 254     elem->prev->next = elem->next;
 255   }else{
 256     pH->first = elem->next;
 257   }
 258   if( elem->next ){
 259     elem->next->prev = elem->prev;
 260   }
 261   pEntry = &pH->ht[h];
 262   if( pEntry->chain==elem ){
 263     pEntry->chain = elem->next;
 264   }
 265   pEntry->count--;
 266   if( pEntry->count<=0 ){
 267     pEntry->chain = 0;
 268   }
 269   if( pH->copyKey && elem->pKey ){
 270     fts2HashFree(elem->pKey);
 271   }
 272   fts2HashFree( elem );
 273   pH->count--;
 274   if( pH->count<=0 ){
 275     assert( pH->first==0 );
 276     assert( pH->count==0 );
 277     fts2HashClear(pH);
 278   }
 279 }
 280
 281 /* Attempt to locate an element of the hash table pH with a key
 282 ** that matches pKey,nKey.  Return the data for this element if it is
 283 ** found, or NULL if there is no match.
 284 */
 285 void *sqlite3Fts2HashFind(const fts2Hash *pH, const void *pKey, int nKey){
 286   int h;                 /* A hash on key */
 287   fts2HashElem *elem;    /* The element that matches key */
 288   int (*xHash)(const void*,int);  /* The hash function */
 289
 290   if( pH==0 || pH->ht==0 ) return 0;
 291   xHash = hashFunction(pH->keyClass);
 292   assert( xHash!=0 );
 293   h = (*xHash)(pKey,nKey);
 294   assert( (pH->htsize & (pH->htsize-1))==0 );
 295   elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
 296   return elem ? elem->data : 0;
 297 }
 298
 299 /* Insert an element into the hash table pH.  The key is pKey,nKey
 300 ** and the data is "data".
 301 **
 302 ** If no element exists with a matching key, then a new
 303 ** element is created.  A copy of the key is made if the copyKey
 304 ** flag is set.  NULL is returned.
 305 **
 306 ** If another element already exists with the same key, then the
 307 ** new data replaces the old data and the old data is returned.
 308 ** The key is not copied in this instance.  If a malloc fails, then
 309 ** the new data is returned and the hash table is unchanged.
 310 **
 311 ** If the "data" parameter to this function is NULL, then the
 312 ** element corresponding to "key" is removed from the hash table.
 313 */
 314 void *sqlite3Fts2HashInsert(
 315   fts2Hash *pH,        /* The hash table to insert into */
 316   const void *pKey,    /* The key */
 317   int nKey,            /* Number of bytes in the key */
 318   void *data           /* The data */
 319 ){
 320   int hraw;                 /* Raw hash value of the key */
 321   int h;                    /* the hash of the key modulo hash table size */
 322   fts2HashElem *elem;       /* Used to loop thru the element list */
 323   fts2HashElem *new_elem;   /* New element added to the pH */
 324   int (*xHash)(const void*,int);  /* The hash function */
 325
 326   assert( pH!=0 );
 327   xHash = hashFunction(pH->keyClass);
 328   assert( xHash!=0 );
 329   hraw = (*xHash)(pKey, nKey);
 330   assert( (pH->htsize & (pH->htsize-1))==0 );
 331   h = hraw & (pH->htsize-1);
 332   elem = findElementGivenHash(pH,pKey,nKey,h);
 333   if( elem ){
 334     void *old_data = elem->data;
 335     if( data==0 ){
 336       removeElementGivenHash(pH,elem,h);
 337     }else{
 338       elem->data = data;
 339     }
 340     return old_data;
 341   }
 342   if( data==0 ) return 0;
 343   new_elem = (fts2HashElem*)fts2HashMalloc( sizeof(fts2HashElem) );
 344   if( new_elem==0 ) return data;
 345   if( pH->copyKey && pKey!=0 ){
 346     new_elem->pKey = fts2HashMalloc( nKey );
 347     if( new_elem->pKey==0 ){
 348       fts2HashFree(new_elem);
 349       return data;
 350     }
 351     memcpy((void*)new_elem->pKey, pKey, nKey);
 352   }else{
 353     new_elem->pKey = (void*)pKey;
 354   }
 355   new_elem->nKey = nKey;
 356   pH->count++;
 357   if( pH->htsize==0 ){
 358     rehash(pH,8);
 359     if( pH->htsize==0 ){
 360       pH->count = 0;
 361       fts2HashFree(new_elem);
 362       return data;
 363     }
 364   }
 365   if( pH->count > pH->htsize ){
 366     rehash(pH,pH->htsize*2);
 367   }
 368   assert( pH->htsize>0 );
 369   assert( (pH->htsize & (pH->htsize-1))==0 );
 370   h = hraw & (pH->htsize-1);
 371   insertElement(pH, &pH->ht[h], new_elem);
 372   new_elem->data = data;
 373   return 0;
 374 }
 375
 376 #endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2) */