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) */