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 ** $Id: hash.cpp 1282 2008-11-13 09:31:33Z LarsPson $

    16 */

    17 #include "sqliteInt.h"

    18 #include <assert.h>

    19 

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

    21 ** fields of the Hash structure.

    22 **

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

    24 ** keyClass is one of the constants SQLITE_HASH_INT, SQLITE_HASH_POINTER,

    25 ** SQLITE_HASH_BINARY, or SQLITE_HASH_STRING.  The value of keyClass 

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

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

    28 ** false if it should just use the supplied pointer.  CopyKey only makes

    29 ** sense for SQLITE_HASH_STRING and SQLITE_HASH_BINARY and is ignored

    30 ** for other key classes.

    31 */

    32 void sqlite3HashInit(Hash *pNew, int keyClass, int copyKey){

    33   assert( pNew!=0 );

    34   assert( keyClass>=SQLITE_HASH_STRING && keyClass<=SQLITE_HASH_BINARY );

    35   pNew->keyClass = keyClass;

    36 #if 0

    37   if( keyClass==SQLITE_HASH_POINTER || keyClass==SQLITE_HASH_INT ) copyKey = 0;

    38 #endif

    39   pNew->copyKey = copyKey;

    40   pNew->first = 0;

    41   pNew->count = 0;

    42   pNew->htsize = 0;

    43   pNew->ht = 0;

    44 }

    45 

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

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

    48 ** to the empty state.

    49 */

    50 void sqlite3HashClear(Hash *pH){

    51   HashElem *elem;         /* For looping over all elements of the table */

    52 

    53   assert( pH!=0 );

    54   elem = pH->first;

    55   pH->first = 0;

    56   if( pH->ht ) sqlite3_free(pH->ht);

    57   pH->ht = 0;

    58   pH->htsize = 0;

    59   while( elem ){

    60     HashElem *next_elem = elem->next;

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

    62       sqlite3_free(elem->pKey);

    63     }

    64     sqlite3_free(elem);

    65     elem = next_elem;

    66   }

    67   pH->count = 0;

    68 }

    69 

    70 #if 0 /* NOT USED */

    71 /*

    72 ** Hash and comparison functions when the mode is SQLITE_HASH_INT

    73 */

    74 static int intHash(const void *pKey, int nKey){

    75   return nKey ^ (nKey<<8) ^ (nKey>>8);

    76 }

    77 static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){

    78   return n2 - n1;

    79 }

    80 #endif

    81 

    82 #if 0 /* NOT USED */

    83 /*

    84 ** Hash and comparison functions when the mode is SQLITE_HASH_POINTER

    85 */

    86 static int ptrHash(const void *pKey, int nKey){

    87   uptr x = Addr(pKey);

    88   return x ^ (x<<8) ^ (x>>8);

    89 }

    90 static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){

    91   if( pKey1==pKey2 ) return 0;

    92   if( pKey1<pKey2 ) return -1;

    93   return 1;

    94 }

    95 #endif

    96 

    97 /*

    98 ** Hash and comparison functions when the mode is SQLITE_HASH_STRING

    99 */

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

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

   102   int h = 0;

   103   if( nKey<=0 ) nKey = strlen(z);

   104   while( nKey > 0  ){

   105     h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++];

   106     nKey--;

   107   }

   108   return h & 0x7fffffff;

   109 }

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

   111   if( n1!=n2 ) return 1;

   112   return sqlite3StrNICmp((const char*)pKey1,(const char*)pKey2,n1);

   113 }

   114 

   115 /*

   116 ** Hash and comparison functions when the mode is SQLITE_HASH_BINARY

   117 */

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

   119   int h = 0;

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

   121   while( nKey-- > 0 ){

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

   123   }

   124   return h & 0x7fffffff;

   125 }

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

   127   if( n1!=n2 ) return 1;

   128   return memcmp(pKey1,pKey2,n1);

   129 }

   130 

   131 /*

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

   133 **

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

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

   136 **

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

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

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

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

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

   142 */

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

   144 #if 0  /* HASH_INT and HASH_POINTER are never used */

   145   switch( keyClass ){

   146     case SQLITE_HASH_INT:     return &intHash;

   147     case SQLITE_HASH_POINTER: return &ptrHash;

   148     case SQLITE_HASH_STRING:  return &strHash;

   149     case SQLITE_HASH_BINARY:  return &binHash;;

   150     default: break;

   151   }

   152   return 0;

   153 #else

   154   if( keyClass==SQLITE_HASH_STRING ){

   155     return &strHash;

   156   }else{

   157     assert( keyClass==SQLITE_HASH_BINARY );

   158     return &binHash;

   159   }

   160 #endif

   161 }

   162 

   163 /*

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

   165 **

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

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

   168 */

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

   170 #if 0 /* HASH_INT and HASH_POINTER are never used */

   171   switch( keyClass ){

   172     case SQLITE_HASH_INT:     return &intCompare;

   173     case SQLITE_HASH_POINTER: return &ptrCompare;

   174     case SQLITE_HASH_STRING:  return &strCompare;

   175     case SQLITE_HASH_BINARY:  return &binCompare;

   176     default: break;

   177   }

   178   return 0;

   179 #else

   180   if( keyClass==SQLITE_HASH_STRING ){

   181     return &strCompare;

   182   }else{

   183     assert( keyClass==SQLITE_HASH_BINARY );

   184     return &binCompare;

   185   }

   186 #endif

   187 }

   188 

   189 /* Link an element into the hash table

   190 */

   191 static void insertElement(

   192   Hash *pH,              /* The complete hash table */

   193   Hash::_ht *pEntry,    /* The entry into which pNew is inserted */

   194   HashElem *pNew         /* The element to be inserted */

   195 ){

   196   HashElem *pHead;       /* First element already in pEntry */

   197   pHead = pEntry->chain;

   198   if( pHead ){

   199     pNew->next = pHead;

   200     pNew->prev = pHead->prev;

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

   202     else             { pH->first = pNew; }

   203     pHead->prev = pNew;

   204   }else{

   205     pNew->next = pH->first;

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

   207     pNew->prev = 0;

   208     pH->first = pNew;

   209   }

   210   pEntry->count++;

   211   pEntry->chain = pNew;

   212 }

   213 

   214 

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

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

   217 ** to resize if sqlite3_malloc() fails.

   218 */

   219 static void rehash(Hash *pH, int new_size){

   220   Hash::_ht *new_ht;            /* The new hash table */

   221   HashElem *elem, *next_elem;    /* For looping over existing elements */

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

   223 

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

   225 

   226   /* There is a call to sqlite3_malloc() inside rehash(). If there is

   227   ** already an allocation at pH->ht, then if this malloc() fails it

   228   ** is benign (since failing to resize a hash table is a performance

   229   ** hit only, not a fatal error).

   230   */

   231   sqlite3MallocBenignFailure(pH->htsize>0);

   232 

   233   new_ht = (Hash::_ht *)sqlite3MallocZero( new_size*sizeof(Hash::_ht) );

   234   if( new_ht==0 ) return;

   235   if( pH->ht ) sqlite3_free(pH->ht);

   236   pH->ht = new_ht;

   237   pH->htsize = new_size;

   238   xHash = hashFunction(pH->keyClass);

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

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

   241     next_elem = elem->next;

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

   243   }

   244 }

   245 

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

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

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

   249 */

   250 static HashElem *findElementGivenHash(

   251   const Hash *pH,     /* The pH to be searched */

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

   253   int nKey,

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

   255 ){

   256   HashElem *elem;                /* Used to loop thru the element list */

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

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

   259 

   260   if( pH->ht ){

   261 	  Hash::_ht *pEntry = &pH->ht[h];

   262     elem = pEntry->chain;

   263     count = pEntry->count;

   264     xCompare = compareFunction(pH->keyClass);

   265     while( count-- && elem ){

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

   267         return elem;

   268       }

   269       elem = elem->next;

   270     }

   271   }

   272   return 0;

   273 }

   274 

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

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

   277 */

   278 static void removeElementGivenHash(

   279   Hash *pH,         /* The pH containing "elem" */

   280   HashElem* elem,   /* The element to be removed from the pH */

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

   282 ){

   283 	Hash::_ht *pEntry;

   284   if( elem->prev ){

   285     elem->prev->next = elem->next; 

   286   }else{

   287     pH->first = elem->next;

   288   }

   289   if( elem->next ){

   290     elem->next->prev = elem->prev;

   291   }

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

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

   294     pEntry->chain = elem->next;

   295   }

   296   pEntry->count--;

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

   298     pEntry->chain = 0;

   299   }

   300   if( pH->copyKey ){

   301     sqlite3_free(elem->pKey);

   302   }

   303   sqlite3_free( elem );

   304   pH->count--;

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

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

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

   308     sqlite3HashClear(pH);

   309   }

   310 }

   311 

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

   313 ** that matches pKey,nKey.  Return a pointer to the corresponding 

   314 ** HashElem structure for this element if it is found, or NULL

   315 ** otherwise.

   316 */

   317 HashElem *sqlite3HashFindElem(const Hash *pH, const void *pKey, int nKey){

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

   319   HashElem *elem;    /* The element that matches key */

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

   321 

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

   323   xHash = hashFunction(pH->keyClass);

   324   assert( xHash!=0 );

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

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

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

   328   return elem;

   329 }

   330 

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

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

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

   334 */

   335 void *sqlite3HashFind(const Hash *pH, const void *pKey, int nKey){

   336   HashElem *elem;    /* The element that matches key */

   337   elem = sqlite3HashFindElem(pH, pKey, nKey);

   338   return elem ? elem->data : 0;

   339 }

   340 

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

   342 ** and the data is "data".

   343 **

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

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

   346 ** flag is set.  NULL is returned.

   347 **

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

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

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

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

   352 **

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

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

   355 */

   356 void *sqlite3HashInsert(Hash *pH, const void *pKey, int nKey, void *data){

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

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

   359   HashElem *elem;       /* Used to loop thru the element list */

   360   HashElem *new_elem;   /* New element added to the pH */

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

   362 

   363   assert( pH!=0 );

   364   xHash = hashFunction(pH->keyClass);

   365   assert( xHash!=0 );

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

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

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

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

   370   if( elem ){

   371     void *old_data = elem->data;

   372     if( data==0 ){

   373       removeElementGivenHash(pH,elem,h);

   374     }else{

   375       elem->data = data;

   376       if( !pH->copyKey ){

   377         elem->pKey = (void *)pKey;

   378       }

   379       assert(nKey==elem->nKey);

   380     }

   381     return old_data;

   382   }

   383   if( data==0 ) return 0;

   384   new_elem = (HashElem*)sqlite3_malloc( sizeof(HashElem) );

   385   if( new_elem==0 ) return data;

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

   387     new_elem->pKey = sqlite3_malloc( nKey );

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

   389       sqlite3_free(new_elem);

   390       return data;

   391     }

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

   393   }else{

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

   395   }

   396   new_elem->nKey = nKey;

   397   pH->count++;

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

   399     rehash(pH,8);

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

   401       pH->count = 0;

   402       if( pH->copyKey ){

   403         sqlite3_free(new_elem->pKey);

   404       }

   405       sqlite3_free(new_elem);

   406       return data;

   407     }

   408   }

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

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

   411   }

   412   assert( pH->htsize>0 );

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

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

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

   416   new_elem->data = data;

   417   return 0;

   418 }