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 "fts2_hash.h"

    34 

    35 /*

    36 ** Malloc and Free functions

    37 */

    38 static void *fts2HashMalloc(int n){

    39   void *p = sqlite3_malloc(n);

    40   if( p ){

    41     memset(p, 0, n);

    42   }

    43   return p;

    44 }

    45 static void fts2HashFree(void *p){

    46   sqlite3_free(p);

    47 }

    48 

    49 /* Turn bulk memory into a hash table object by initializing the

    50 ** fields of the Hash structure.

    51 **

    52 ** "pNew" is a pointer to the hash table that is to be initialized.

    53 ** keyClass is one of the constants 

    54 ** FTS2_HASH_BINARY or FTS2_HASH_STRING.  The value of keyClass 

    55 ** determines what kind of key the hash table will use.  "copyKey" is

    56 ** true if the hash table should make its own private copy of keys and

    57 ** false if it should just use the supplied pointer.

    58 */

    59 void sqlite3Fts2HashInit(fts2Hash *pNew, int keyClass, int copyKey){

    60   assert( pNew!=0 );

    61   assert( keyClass>=FTS2_HASH_STRING && keyClass<=FTS2_HASH_BINARY );

    62   pNew->keyClass = keyClass;

    63   pNew->copyKey = copyKey;

    64   pNew->first = 0;

    65   pNew->count = 0;

    66   pNew->htsize = 0;

    67   pNew->ht = 0;

    68 }

    69 

    70 /* Remove all entries from a hash table.  Reclaim all memory.

    71 ** Call this routine to delete a hash table or to reset a hash table

    72 ** to the empty state.

    73 */

    74 void sqlite3Fts2HashClear(fts2Hash *pH){

    75   fts2HashElem *elem;         /* For looping over all elements of the table */

    76 

    77   assert( pH!=0 );

    78   elem = pH->first;

    79   pH->first = 0;

    80   fts2HashFree(pH->ht);

    81   pH->ht = 0;

    82   pH->htsize = 0;

    83   while( elem ){

    84     fts2HashElem *next_elem = elem->next;

    85     if( pH->copyKey && elem->pKey ){

    86       fts2HashFree(elem->pKey);

    87     }

    88     fts2HashFree(elem);

    89     elem = next_elem;

    90   }

    91   pH->count = 0;

    92 }

    93 

    94 /*

    95 ** Hash and comparison functions when the mode is FTS2_HASH_STRING

    96 */

    97 static int strHash(const void *pKey, int nKey){

    98   const char *z = (const char *)pKey;

    99   int h = 0;

   100   if( nKey<=0 ) nKey = (int) strlen(z);

   101   while( nKey > 0  ){

   102     h = (h<<3) ^ h ^ *z++;

   103     nKey--;

   104   }

   105   return h & 0x7fffffff;

   106 }

   107 static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){

   108   if( n1!=n2 ) return 1;

   109   return strncmp((const char*)pKey1,(const char*)pKey2,n1);

   110 }

   111 

   112 /*

   113 ** Hash and comparison functions when the mode is FTS2_HASH_BINARY

   114 */

   115 static int binHash(const void *pKey, int nKey){

   116   int h = 0;

   117   const char *z = (const char *)pKey;

   118   while( nKey-- > 0 ){

   119     h = (h<<3) ^ h ^ *(z++);

   120   }

   121   return h & 0x7fffffff;

   122 }

   123 static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){

   124   if( n1!=n2 ) return 1;

   125   return memcmp(pKey1,pKey2,n1);

   126 }

   127 

   128 /*

   129 ** Return a pointer to the appropriate hash function given the key class.

   130 **

   131 ** The C syntax in this function definition may be unfamilar to some 

   132 ** programmers, so we provide the following additional explanation:

   133 **

   134 ** The name of the function is "hashFunction".  The function takes a

   135 ** single parameter "keyClass".  The return value of hashFunction()

   136 ** is a pointer to another function.  Specifically, the return value

   137 ** of hashFunction() is a pointer to a function that takes two parameters

   138 ** with types "const void*" and "int" and returns an "int".

   139 */

   140 static int (*hashFunction(int keyClass))(const void*,int){

   141   if( keyClass==FTS2_HASH_STRING ){

   142     return &strHash;

   143   }else{

   144     assert( keyClass==FTS2_HASH_BINARY );

   145     return &binHash;

   146   }

   147 }

   148 

   149 /*

   150 ** Return a pointer to the appropriate hash function given the key class.

   151 **

   152 ** For help in interpreted the obscure C code in the function definition,

   153 ** see the header comment on the previous function.

   154 */

   155 static int (*compareFunction(int keyClass))(const void*,int,const void*,int){

   156   if( keyClass==FTS2_HASH_STRING ){

   157     return &strCompare;

   158   }else{

   159     assert( keyClass==FTS2_HASH_BINARY );

   160     return &binCompare;

   161   }

   162 }

   163 

   164 /* Link an element into the hash table

   165 */

   166 static void insertElement(

   167   fts2Hash *pH,            /* The complete hash table */

   168   struct _fts2ht *pEntry,  /* The entry into which pNew is inserted */

   169   fts2HashElem *pNew       /* The element to be inserted */

   170 ){

   171   fts2HashElem *pHead;     /* First element already in pEntry */

   172   pHead = pEntry->chain;

   173   if( pHead ){

   174     pNew->next = pHead;

   175     pNew->prev = pHead->prev;

   176     if( pHead->prev ){ pHead->prev->next = pNew; }

   177     else             { pH->first = pNew; }

   178     pHead->prev = pNew;

   179   }else{

   180     pNew->next = pH->first;

   181     if( pH->first ){ pH->first->prev = pNew; }

   182     pNew->prev = 0;

   183     pH->first = pNew;

   184   }

   185   pEntry->count++;

   186   pEntry->chain = pNew;

   187 }

   188 

   189 

   190 /* Resize the hash table so that it cantains "new_size" buckets.

   191 ** "new_size" must be a power of 2.  The hash table might fail 

   192 ** to resize if sqliteMalloc() fails.

   193 */

   194 static void rehash(fts2Hash *pH, int new_size){

   195   struct _fts2ht *new_ht;          /* The new hash table */

   196   fts2HashElem *elem, *next_elem;  /* For looping over existing elements */

   197   int (*xHash)(const void*,int);   /* The hash function */

   198 

   199   assert( (new_size & (new_size-1))==0 );

   200   new_ht = (struct _fts2ht *)fts2HashMalloc( new_size*sizeof(struct _fts2ht) );

   201   if( new_ht==0 ) return;

   202   fts2HashFree(pH->ht);

   203   pH->ht = new_ht;

   204   pH->htsize = new_size;

   205   xHash = hashFunction(pH->keyClass);

   206   for(elem=pH->first, pH->first=0; elem; elem = next_elem){

   207     int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);

   208     next_elem = elem->next;

   209     insertElement(pH, &new_ht[h], elem);

   210   }

   211 }

   212 

   213 /* This function (for internal use only) locates an element in an

   214 ** hash table that matches the given key.  The hash for this key has

   215 ** already been computed and is passed as the 4th parameter.

   216 */

   217 static fts2HashElem *findElementGivenHash(

   218   const fts2Hash *pH, /* The pH to be searched */

   219   const void *pKey,   /* The key we are searching for */

   220   int nKey,

   221   int h               /* The hash for this key. */

   222 ){

   223   fts2HashElem *elem;            /* Used to loop thru the element list */

   224   int count;                     /* Number of elements left to test */

   225   int (*xCompare)(const void*,int,const void*,int);  /* comparison function */

   226 

   227   if( pH->ht ){

   228     struct _fts2ht *pEntry = &pH->ht[h];

   229     elem = pEntry->chain;

   230     count = pEntry->count;

   231     xCompare = compareFunction(pH->keyClass);

   232     while( count-- && elem ){

   233       if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){ 

   234         return elem;

   235       }

   236       elem = elem->next;

   237     }

   238   }

   239   return 0;

   240 }

   241 

   242 /* Remove a single entry from the hash table given a pointer to that

   243 ** element and a hash on the element's key.

   244 */

   245 static void removeElementGivenHash(

   246   fts2Hash *pH,         /* The pH containing "elem" */

   247   fts2HashElem* elem,   /* The element to be removed from the pH */

   248   int h                 /* Hash value for the element */

   249 ){

   250   struct _fts2ht *pEntry;

   251   if( elem->prev ){

   252     elem->prev->next = elem->next; 

   253   }else{

   254     pH->first = elem->next;

   255   }

   256   if( elem->next ){

   257     elem->next->prev = elem->prev;

   258   }

   259   pEntry = &pH->ht[h];

   260   if( pEntry->chain==elem ){

   261     pEntry->chain = elem->next;

   262   }

   263   pEntry->count--;

   264   if( pEntry->count<=0 ){

   265     pEntry->chain = 0;

   266   }

   267   if( pH->copyKey && elem->pKey ){

   268     fts2HashFree(elem->pKey);

   269   }

   270   fts2HashFree( elem );

   271   pH->count--;

   272   if( pH->count<=0 ){

   273     assert( pH->first==0 );

   274     assert( pH->count==0 );

   275     fts2HashClear(pH);

   276   }

   277 }

   278 

   279 /* Attempt to locate an element of the hash table pH with a key

   280 ** that matches pKey,nKey.  Return the data for this element if it is

   281 ** found, or NULL if there is no match.

   282 */

   283 void *sqlite3Fts2HashFind(const fts2Hash *pH, const void *pKey, int nKey){

   284   int h;                 /* A hash on key */

   285   fts2HashElem *elem;    /* The element that matches key */

   286   int (*xHash)(const void*,int);  /* The hash function */

   287 

   288   if( pH==0 || pH->ht==0 ) return 0;

   289   xHash = hashFunction(pH->keyClass);

   290   assert( xHash!=0 );

   291   h = (*xHash)(pKey,nKey);

   292   assert( (pH->htsize & (pH->htsize-1))==0 );

   293   elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));

   294   return elem ? elem->data : 0;

   295 }

   296 

   297 /* Insert an element into the hash table pH.  The key is pKey,nKey

   298 ** and the data is "data".

   299 **

   300 ** If no element exists with a matching key, then a new

   301 ** element is created.  A copy of the key is made if the copyKey

   302 ** flag is set.  NULL is returned.

   303 **

   304 ** If another element already exists with the same key, then the

   305 ** new data replaces the old data and the old data is returned.

   306 ** The key is not copied in this instance.  If a malloc fails, then

   307 ** the new data is returned and the hash table is unchanged.

   308 **

   309 ** If the "data" parameter to this function is NULL, then the

   310 ** element corresponding to "key" is removed from the hash table.

   311 */

   312 void *sqlite3Fts2HashInsert(

   313   fts2Hash *pH,        /* The hash table to insert into */

   314   const void *pKey,    /* The key */

   315   int nKey,            /* Number of bytes in the key */

   316   void *data           /* The data */

   317 ){

   318   int hraw;                 /* Raw hash value of the key */

   319   int h;                    /* the hash of the key modulo hash table size */

   320   fts2HashElem *elem;       /* Used to loop thru the element list */

   321   fts2HashElem *new_elem;   /* New element added to the pH */

   322   int (*xHash)(const void*,int);  /* The hash function */

   323 

   324   assert( pH!=0 );

   325   xHash = hashFunction(pH->keyClass);

   326   assert( xHash!=0 );

   327   hraw = (*xHash)(pKey, nKey);

   328   assert( (pH->htsize & (pH->htsize-1))==0 );

   329   h = hraw & (pH->htsize-1);

   330   elem = findElementGivenHash(pH,pKey,nKey,h);

   331   if( elem ){

   332     void *old_data = elem->data;

   333     if( data==0 ){

   334       removeElementGivenHash(pH,elem,h);

   335     }else{

   336       elem->data = data;

   337     }

   338     return old_data;

   339   }

   340   if( data==0 ) return 0;

   341   new_elem = (fts2HashElem*)fts2HashMalloc( sizeof(fts2HashElem) );

   342   if( new_elem==0 ) return data;

   343   if( pH->copyKey && pKey!=0 ){

   344     new_elem->pKey = fts2HashMalloc( nKey );

   345     if( new_elem->pKey==0 ){

   346       fts2HashFree(new_elem);

   347       return data;

   348     }

   349     memcpy((void*)new_elem->pKey, pKey, nKey);

   350   }else{

   351     new_elem->pKey = (void*)pKey;

   352   }

   353   new_elem->nKey = nKey;

   354   pH->count++;

   355   if( pH->htsize==0 ){

   356     rehash(pH,8);

   357     if( pH->htsize==0 ){

   358       pH->count = 0;

   359       fts2HashFree(new_elem);

   360       return data;

   361     }

   362   }

   363   if( pH->count > pH->htsize ){

   364     rehash(pH,pH->htsize*2);

   365   }

   366   assert( pH->htsize>0 );

   367   assert( (pH->htsize & (pH->htsize-1))==0 );

   368   h = hraw & (pH->htsize-1);

   369   insertElement(pH, &pH->ht[h], new_elem);

   370   new_elem->data = data;

   371   return 0;

   372 }

   373 

   374 #endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2) */