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.c,v 1.30 2008/06/20 14:59:51 danielk1977 Exp $

    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   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   struct _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   struct _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 #ifdef SQLITE_MALLOC_SOFT_LIMIT

   225   if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){

   226     new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht);

   227   }

   228   if( new_size==pH->htsize ) return;

   229 #endif

   230 

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

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

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

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

   235   */

   236   if( pH->htsize>0 ) sqlite3BeginBenignMalloc();

   237   new_ht = (struct _ht *)sqlite3MallocZero( new_size*sizeof(struct _ht) );

   238   if( pH->htsize>0 ) sqlite3EndBenignMalloc();

   239 

   240   if( new_ht==0 ) return;

   241   sqlite3_free(pH->ht);

   242   pH->ht = new_ht;

   243   pH->htsize = new_size;

   244   xHash = hashFunction(pH->keyClass);

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

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

   247     next_elem = elem->next;

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

   249   }

   250 }

   251 

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

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

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

   255 */

   256 static HashElem *findElementGivenHash(

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

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

   259   int nKey,

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

   261 ){

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

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

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

   265 

   266   if( pH->ht ){

   267     struct _ht *pEntry = &pH->ht[h];

   268     elem = pEntry->chain;

   269     count = pEntry->count;

   270     xCompare = compareFunction(pH->keyClass);

   271     while( count-- && elem ){

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

   273         return elem;

   274       }

   275       elem = elem->next;

   276     }

   277   }

   278   return 0;

   279 }

   280 

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

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

   283 */

   284 static void removeElementGivenHash(

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

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

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

   288 ){

   289   struct _ht *pEntry;

   290   if( elem->prev ){

   291     elem->prev->next = elem->next; 

   292   }else{

   293     pH->first = elem->next;

   294   }

   295   if( elem->next ){

   296     elem->next->prev = elem->prev;

   297   }

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

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

   300     pEntry->chain = elem->next;

   301   }

   302   pEntry->count--;

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

   304     pEntry->chain = 0;

   305   }

   306   if( pH->copyKey ){

   307     sqlite3_free(elem->pKey);

   308   }

   309   sqlite3_free( elem );

   310   pH->count--;

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

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

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

   314     sqlite3HashClear(pH);

   315   }

   316 }

   317 

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

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

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

   321 ** otherwise.

   322 */

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

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

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

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

   327 

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

   329   xHash = hashFunction(pH->keyClass);

   330   assert( xHash!=0 );

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

   332   elem = findElementGivenHash(pH,pKey,nKey, h % pH->htsize);

   333   return elem;

   334 }

   335 

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

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

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

   339 */

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

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

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

   343   return elem ? elem->data : 0;

   344 }

   345 

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

   347 ** and the data is "data".

   348 **

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

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

   351 ** flag is set.  NULL is returned.

   352 **

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

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

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

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

   357 **

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

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

   360 */

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

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

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

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

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

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

   367 

   368   assert( pH!=0 );

   369   xHash = hashFunction(pH->keyClass);

   370   assert( xHash!=0 );

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

   372   if( pH->htsize ){

   373     h = hraw % pH->htsize;

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

   375     if( elem ){

   376       void *old_data = elem->data;

   377       if( data==0 ){

   378         removeElementGivenHash(pH,elem,h);

   379       }else{

   380         elem->data = data;

   381         if( !pH->copyKey ){

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

   383         }

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

   385       }

   386       return old_data;

   387     }

   388   }

   389   if( data==0 ) return 0;

   390   new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );

   391   if( new_elem==0 ) return data;

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

   393     new_elem->pKey = sqlite3Malloc( nKey );

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

   395       sqlite3_free(new_elem);

   396       return data;

   397     }

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

   399   }else{

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

   401   }

   402   new_elem->nKey = nKey;

   403   pH->count++;

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

   405     rehash(pH, 128/sizeof(pH->ht[0]));

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

   407       pH->count = 0;

   408       if( pH->copyKey ){

   409         sqlite3_free(new_elem->pKey);

   410       }

   411       sqlite3_free(new_elem);

   412       return data;

   413     }

   414   }

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

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

   417   }

   418   assert( pH->htsize>0 );

   419   h = hraw % pH->htsize;

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

   421   new_elem->data = data;

   422   return 0;

   423 }