ext/fts1/fts1_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 #include <assert.h>
  17 #include <stdlib.h>
  18 #include <string.h>
  19
  20 /*
  21 ** The code in this file is only compiled if:
  22 **
  23 **     * The FTS1 module is being built as an extension
  24 **       (in which case SQLITE_CORE is not defined), or
  25 **
  26 **     * The FTS1 module is being built into the core of
  27 **       SQLite (in which case SQLITE_ENABLE_FTS1 is defined).
  28 */
  29 #if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS1)
  30
  31
  32 #include "fts1_hash.h"
  33
  34 static void *malloc_and_zero(int n){
  35   void *p = malloc(n);
  36   if( p ){
  37     memset(p, 0, n);
  38   }
  39   return p;
  40 }
  41
  42 /* Turn bulk memory into a hash table object by initializing the
  43 ** fields of the Hash structure.
  44 **
  45 ** "pNew" is a pointer to the hash table that is to be initialized.
  46 ** keyClass is one of the constants
  47 ** FTS1_HASH_BINARY or FTS1_HASH_STRING.  The value of keyClass
  48 ** determines what kind of key the hash table will use.  "copyKey" is
  49 ** true if the hash table should make its own private copy of keys and
  50 ** false if it should just use the supplied pointer.
  51 */
  52 void sqlite3Fts1HashInit(fts1Hash *pNew, int keyClass, int copyKey){
  53   assert( pNew!=0 );
  54   assert( keyClass>=FTS1_HASH_STRING && keyClass<=FTS1_HASH_BINARY );
  55   pNew->keyClass = keyClass;
  56   pNew->copyKey = copyKey;
  57   pNew->first = 0;
  58   pNew->count = 0;
  59   pNew->htsize = 0;
  60   pNew->ht = 0;
  61   pNew->xMalloc = malloc_and_zero;
  62   pNew->xFree = free;
  63 }
  64
  65 /* Remove all entries from a hash table.  Reclaim all memory.
  66 ** Call this routine to delete a hash table or to reset a hash table
  67 ** to the empty state.
  68 */
  69 void sqlite3Fts1HashClear(fts1Hash *pH){
  70   fts1HashElem *elem;         /* For looping over all elements of the table */
  71
  72   assert( pH!=0 );
  73   elem = pH->first;
  74   pH->first = 0;
  75   if( pH->ht ) pH->xFree(pH->ht);
  76   pH->ht = 0;
  77   pH->htsize = 0;
  78   while( elem ){
  79     fts1HashElem *next_elem = elem->next;
  80     if( pH->copyKey && elem->pKey ){
  81       pH->xFree(elem->pKey);
  82     }
  83     pH->xFree(elem);
  84     elem = next_elem;
  85   }
  86   pH->count = 0;
  87 }
  88
  89 /*
  90 ** Hash and comparison functions when the mode is FTS1_HASH_STRING
  91 */
  92 static int strHash(const void *pKey, int nKey){
  93   const char *z = (const char *)pKey;
  94   int h = 0;
  95   if( nKey<=0 ) nKey = (int) strlen(z);
  96   while( nKey > 0  ){
  97     h = (h<<3) ^ h ^ *z++;
  98     nKey--;
  99   }
 100   return h & 0x7fffffff;
 101 }
 102 static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
 103   if( n1!=n2 ) return 1;
 104   return strncmp((const char*)pKey1,(const char*)pKey2,n1);
 105 }
 106
 107 /*
 108 ** Hash and comparison functions when the mode is FTS1_HASH_BINARY
 109 */
 110 static int binHash(const void *pKey, int nKey){
 111   int h = 0;
 112   const char *z = (const char *)pKey;
 113   while( nKey-- > 0 ){
 114     h = (h<<3) ^ h ^ *(z++);
 115   }
 116   return h & 0x7fffffff;
 117 }
 118 static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
 119   if( n1!=n2 ) return 1;
 120   return memcmp(pKey1,pKey2,n1);
 121 }
 122
 123 /*
 124 ** Return a pointer to the appropriate hash function given the key class.
 125 **
 126 ** The C syntax in this function definition may be unfamilar to some
 127 ** programmers, so we provide the following additional explanation:
 128 **
 129 ** The name of the function is "hashFunction".  The function takes a
 130 ** single parameter "keyClass".  The return value of hashFunction()
 131 ** is a pointer to another function.  Specifically, the return value
 132 ** of hashFunction() is a pointer to a function that takes two parameters
 133 ** with types "const void*" and "int" and returns an "int".
 134 */
 135 static int (*hashFunction(int keyClass))(const void*,int){
 136   if( keyClass==FTS1_HASH_STRING ){
 137     return &strHash;
 138   }else{
 139     assert( keyClass==FTS1_HASH_BINARY );
 140     return &binHash;
 141   }
 142 }
 143
 144 /*
 145 ** Return a pointer to the appropriate hash function given the key class.
 146 **
 147 ** For help in interpreted the obscure C code in the function definition,
 148 ** see the header comment on the previous function.
 149 */
 150 static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
 151   if( keyClass==FTS1_HASH_STRING ){
 152     return &strCompare;
 153   }else{
 154     assert( keyClass==FTS1_HASH_BINARY );
 155     return &binCompare;
 156   }
 157 }
 158
 159 /* Link an element into the hash table
 160 */
 161 static void insertElement(
 162   fts1Hash *pH,            /* The complete hash table */
 163   struct _fts1ht *pEntry,  /* The entry into which pNew is inserted */
 164   fts1HashElem *pNew       /* The element to be inserted */
 165 ){
 166   fts1HashElem *pHead;     /* First element already in pEntry */
 167   pHead = pEntry->chain;
 168   if( pHead ){
 169     pNew->next = pHead;
 170     pNew->prev = pHead->prev;
 171     if( pHead->prev ){ pHead->prev->next = pNew; }
 172     else             { pH->first = pNew; }
 173     pHead->prev = pNew;
 174   }else{
 175     pNew->next = pH->first;
 176     if( pH->first ){ pH->first->prev = pNew; }
 177     pNew->prev = 0;
 178     pH->first = pNew;
 179   }
 180   pEntry->count++;
 181   pEntry->chain = pNew;
 182 }
 183
 184
 185 /* Resize the hash table so that it cantains "new_size" buckets.
 186 ** "new_size" must be a power of 2.  The hash table might fail
 187 ** to resize if sqliteMalloc() fails.
 188 */
 189 static void rehash(fts1Hash *pH, int new_size){
 190   struct _fts1ht *new_ht;          /* The new hash table */
 191   fts1HashElem *elem, *next_elem;  /* For looping over existing elements */
 192   int (*xHash)(const void*,int);   /* The hash function */
 193
 194   assert( (new_size & (new_size-1))==0 );
 195   new_ht = (struct _fts1ht *)pH->xMalloc( new_size*sizeof(struct _fts1ht) );
 196   if( new_ht==0 ) return;
 197   if( pH->ht ) pH->xFree(pH->ht);
 198   pH->ht = new_ht;
 199   pH->htsize = new_size;
 200   xHash = hashFunction(pH->keyClass);
 201   for(elem=pH->first, pH->first=0; elem; elem = next_elem){
 202     int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
 203     next_elem = elem->next;
 204     insertElement(pH, &new_ht[h], elem);
 205   }
 206 }
 207
 208 /* This function (for internal use only) locates an element in an
 209 ** hash table that matches the given key.  The hash for this key has
 210 ** already been computed and is passed as the 4th parameter.
 211 */
 212 static fts1HashElem *findElementGivenHash(
 213   const fts1Hash *pH, /* The pH to be searched */
 214   const void *pKey,   /* The key we are searching for */
 215   int nKey,
 216   int h               /* The hash for this key. */
 217 ){
 218   fts1HashElem *elem;            /* Used to loop thru the element list */
 219   int count;                     /* Number of elements left to test */
 220   int (*xCompare)(const void*,int,const void*,int);  /* comparison function */
 221
 222   if( pH->ht ){
 223     struct _fts1ht *pEntry = &pH->ht[h];
 224     elem = pEntry->chain;
 225     count = pEntry->count;
 226     xCompare = compareFunction(pH->keyClass);
 227     while( count-- && elem ){
 228       if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){
 229         return elem;
 230       }
 231       elem = elem->next;
 232     }
 233   }
 234   return 0;
 235 }
 236
 237 /* Remove a single entry from the hash table given a pointer to that
 238 ** element and a hash on the element's key.
 239 */
 240 static void removeElementGivenHash(
 241   fts1Hash *pH,         /* The pH containing "elem" */
 242   fts1HashElem* elem,   /* The element to be removed from the pH */
 243   int h                 /* Hash value for the element */
 244 ){
 245   struct _fts1ht *pEntry;
 246   if( elem->prev ){
 247     elem->prev->next = elem->next;
 248   }else{
 249     pH->first = elem->next;
 250   }
 251   if( elem->next ){
 252     elem->next->prev = elem->prev;
 253   }
 254   pEntry = &pH->ht[h];
 255   if( pEntry->chain==elem ){
 256     pEntry->chain = elem->next;
 257   }
 258   pEntry->count--;
 259   if( pEntry->count<=0 ){
 260     pEntry->chain = 0;
 261   }
 262   if( pH->copyKey && elem->pKey ){
 263     pH->xFree(elem->pKey);
 264   }
 265   pH->xFree( elem );
 266   pH->count--;
 267   if( pH->count<=0 ){
 268     assert( pH->first==0 );
 269     assert( pH->count==0 );
 270     fts1HashClear(pH);
 271   }
 272 }
 273
 274 /* Attempt to locate an element of the hash table pH with a key
 275 ** that matches pKey,nKey.  Return the data for this element if it is
 276 ** found, or NULL if there is no match.
 277 */
 278 void *sqlite3Fts1HashFind(const fts1Hash *pH, const void *pKey, int nKey){
 279   int h;                 /* A hash on key */
 280   fts1HashElem *elem;    /* The element that matches key */
 281   int (*xHash)(const void*,int);  /* The hash function */
 282
 283   if( pH==0 || pH->ht==0 ) return 0;
 284   xHash = hashFunction(pH->keyClass);
 285   assert( xHash!=0 );
 286   h = (*xHash)(pKey,nKey);
 287   assert( (pH->htsize & (pH->htsize-1))==0 );
 288   elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
 289   return elem ? elem->data : 0;
 290 }
 291
 292 /* Insert an element into the hash table pH.  The key is pKey,nKey
 293 ** and the data is "data".
 294 **
 295 ** If no element exists with a matching key, then a new
 296 ** element is created.  A copy of the key is made if the copyKey
 297 ** flag is set.  NULL is returned.
 298 **
 299 ** If another element already exists with the same key, then the
 300 ** new data replaces the old data and the old data is returned.
 301 ** The key is not copied in this instance.  If a malloc fails, then
 302 ** the new data is returned and the hash table is unchanged.
 303 **
 304 ** If the "data" parameter to this function is NULL, then the
 305 ** element corresponding to "key" is removed from the hash table.
 306 */
 307 void *sqlite3Fts1HashInsert(
 308   fts1Hash *pH,        /* The hash table to insert into */
 309   const void *pKey,    /* The key */
 310   int nKey,            /* Number of bytes in the key */
 311   void *data           /* The data */
 312 ){
 313   int hraw;                 /* Raw hash value of the key */
 314   int h;                    /* the hash of the key modulo hash table size */
 315   fts1HashElem *elem;       /* Used to loop thru the element list */
 316   fts1HashElem *new_elem;   /* New element added to the pH */
 317   int (*xHash)(const void*,int);  /* The hash function */
 318
 319   assert( pH!=0 );
 320   xHash = hashFunction(pH->keyClass);
 321   assert( xHash!=0 );
 322   hraw = (*xHash)(pKey, nKey);
 323   assert( (pH->htsize & (pH->htsize-1))==0 );
 324   h = hraw & (pH->htsize-1);
 325   elem = findElementGivenHash(pH,pKey,nKey,h);
 326   if( elem ){
 327     void *old_data = elem->data;
 328     if( data==0 ){
 329       removeElementGivenHash(pH,elem,h);
 330     }else{
 331       elem->data = data;
 332     }
 333     return old_data;
 334   }
 335   if( data==0 ) return 0;
 336   new_elem = (fts1HashElem*)pH->xMalloc( sizeof(fts1HashElem) );
 337   if( new_elem==0 ) return data;
 338   if( pH->copyKey && pKey!=0 ){
 339     new_elem->pKey = pH->xMalloc( nKey );
 340     if( new_elem->pKey==0 ){
 341       pH->xFree(new_elem);
 342       return data;
 343     }
 344     memcpy((void*)new_elem->pKey, pKey, nKey);
 345   }else{
 346     new_elem->pKey = (void*)pKey;
 347   }
 348   new_elem->nKey = nKey;
 349   pH->count++;
 350   if( pH->htsize==0 ){
 351     rehash(pH,8);
 352     if( pH->htsize==0 ){
 353       pH->count = 0;
 354       pH->xFree(new_elem);
 355       return data;
 356     }
 357   }
 358   if( pH->count > pH->htsize ){
 359     rehash(pH,pH->htsize*2);
 360   }
 361   assert( pH->htsize>0 );
 362   assert( (pH->htsize & (pH->htsize-1))==0 );
 363   h = hraw & (pH->htsize-1);
 364   insertElement(pH, &pH->ht[h], new_elem);
 365   new_elem->data = data;
 366   return 0;
 367 }
 368
 369 #endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS1) */