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 1.18 2006/02/14 10:48:39 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   pNew->xMalloc = sqlite3MallocX;

    45   pNew->xFree = sqlite3FreeX;

    46 }

    47 

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

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

    50 ** to the empty state.

    51 */

    52 void sqlite3HashClear(Hash *pH){

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

    54 

    55   assert( pH!=0 );

    56   elem = pH->first;

    57   pH->first = 0;

    58   if( pH->ht ) pH->xFree(pH->ht);

    59   pH->ht = 0;

    60   pH->htsize = 0;

    61   while( elem ){

    62     HashElem *next_elem = elem->next;

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

    64       pH->xFree(elem->pKey);

    65     }

    66     pH->xFree(elem);

    67     elem = next_elem;

    68   }

    69   pH->count = 0;

    70 }

    71 

    72 #if 0 /* NOT USED */

    73 /*

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

    75 */

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

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

    78 }

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

    80   return n2 - n1;

    81 }

    82 #endif

    83 

    84 #if 0 /* NOT USED */

    85 /*

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

    87 */

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

    89   uptr x = Addr(pKey);

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

    91 }

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

    93   if( pKey1==pKey2 ) return 0;

    94   if( pKey1<pKey2 ) return -1;

    95   return 1;

    96 }

    97 #endif

    98 

    99 /*

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

   101 */

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

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

   104   int h = 0;

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

   106   while( nKey > 0  ){

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

   108     nKey--;

   109   }

   110   return h & 0x7fffffff;

   111 }

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

   113   if( n1!=n2 ) return 1;

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

   115 }

   116 

   117 /*

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

   119 */

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

   121   int h = 0;

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

   123   while( nKey-- > 0 ){

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

   125   }

   126   return h & 0x7fffffff;

   127 }

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

   129   if( n1!=n2 ) return 1;

   130   return memcmp(pKey1,pKey2,n1);

   131 }

   132 

   133 /*

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

   135 **

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

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

   138 **

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

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

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

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

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

   144 */

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

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

   147   switch( keyClass ){

   148     case SQLITE_HASH_INT:     return &intHash;

   149     case SQLITE_HASH_POINTER: return &ptrHash;

   150     case SQLITE_HASH_STRING:  return &strHash;

   151     case SQLITE_HASH_BINARY:  return &binHash;;

   152     default: break;

   153   }

   154   return 0;

   155 #else

   156   if( keyClass==SQLITE_HASH_STRING ){

   157     return &strHash;

   158   }else{

   159     assert( keyClass==SQLITE_HASH_BINARY );

   160     return &binHash;

   161   }

   162 #endif

   163 }

   164 

   165 /*

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

   167 **

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

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

   170 */

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

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

   173   switch( keyClass ){

   174     case SQLITE_HASH_INT:     return &intCompare;

   175     case SQLITE_HASH_POINTER: return &ptrCompare;

   176     case SQLITE_HASH_STRING:  return &strCompare;

   177     case SQLITE_HASH_BINARY:  return &binCompare;

   178     default: break;

   179   }

   180   return 0;

   181 #else

   182   if( keyClass==SQLITE_HASH_STRING ){

   183     return &strCompare;

   184   }else{

   185     assert( keyClass==SQLITE_HASH_BINARY );

   186     return &binCompare;

   187   }

   188 #endif

   189 }

   190 

   191 /* Link an element into the hash table

   192 */

   193 static void insertElement(

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

   195   struct _ht *pEntry,    /* The entry into which pNew is inserted */

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

   197 ){

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

   199   pHead = pEntry->chain;

   200   if( pHead ){

   201     pNew->next = pHead;

   202     pNew->prev = pHead->prev;

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

   204     else             { pH->first = pNew; }

   205     pHead->prev = pNew;

   206   }else{

   207     pNew->next = pH->first;

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

   209     pNew->prev = 0;

   210     pH->first = pNew;

   211   }

   212   pEntry->count++;

   213   pEntry->chain = pNew;

   214 }

   215 

   216 

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

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

   219 ** to resize if sqliteMalloc() fails.

   220 */

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

   222   struct _ht *new_ht;            /* The new hash table */

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

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

   225 

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

   227   new_ht = (struct _ht *)pH->xMalloc( new_size*sizeof(struct _ht) );

   228   if( new_ht==0 ) return;

   229   if( pH->ht ) pH->xFree(pH->ht);

   230   pH->ht = new_ht;

   231   pH->htsize = new_size;

   232   xHash = hashFunction(pH->keyClass);

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

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

   235     next_elem = elem->next;

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

   237   }

   238 }

   239 

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

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

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

   243 */

   244 static HashElem *findElementGivenHash(

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

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

   247   int nKey,

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

   249 ){

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

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

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

   253 

   254   if( pH->ht ){

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

   256     elem = pEntry->chain;

   257     count = pEntry->count;

   258     xCompare = compareFunction(pH->keyClass);

   259     while( count-- && elem ){

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

   261         return elem;

   262       }

   263       elem = elem->next;

   264     }

   265   }

   266   return 0;

   267 }

   268 

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

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

   271 */

   272 static void removeElementGivenHash(

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

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

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

   276 ){

   277   struct _ht *pEntry;

   278   if( elem->prev ){

   279     elem->prev->next = elem->next; 

   280   }else{

   281     pH->first = elem->next;

   282   }

   283   if( elem->next ){

   284     elem->next->prev = elem->prev;

   285   }

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

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

   288     pEntry->chain = elem->next;

   289   }

   290   pEntry->count--;

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

   292     pEntry->chain = 0;

   293   }

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

   295     pH->xFree(elem->pKey);

   296   }

   297   pH->xFree( elem );

   298   pH->count--;

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

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

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

   302     sqlite3HashClear(pH);

   303   }

   304 }

   305 

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

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

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

   309 */

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

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

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

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

   314 

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

   316   xHash = hashFunction(pH->keyClass);

   317   assert( xHash!=0 );

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

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

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

   321   return elem ? elem->data : 0;

   322 }

   323 

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

   325 ** and the data is "data".

   326 **

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

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

   329 ** flag is set.  NULL is returned.

   330 **

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

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

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

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

   335 **

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

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

   338 */

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

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

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

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

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

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

   345 

   346   assert( pH!=0 );

   347   xHash = hashFunction(pH->keyClass);

   348   assert( xHash!=0 );

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

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

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

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

   353   if( elem ){

   354     void *old_data = elem->data;

   355     if( data==0 ){

   356       removeElementGivenHash(pH,elem,h);

   357     }else{

   358       elem->data = data;

   359     }

   360     return old_data;

   361   }

   362   if( data==0 ) return 0;

   363   new_elem = (HashElem*)pH->xMalloc( sizeof(HashElem) );

   364   if( new_elem==0 ) return data;

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

   366     new_elem->pKey = pH->xMalloc( nKey );

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

   368       pH->xFree(new_elem);

   369       return data;

   370     }

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

   372   }else{

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

   374   }

   375   new_elem->nKey = nKey;

   376   pH->count++;

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

   378     rehash(pH,8);

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

   380       pH->count = 0;

   381       pH->xFree(new_elem);

   382       return data;

   383     }

   384   }

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

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

   387   }

   388   assert( pH->htsize>0 );

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

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

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

   392   new_elem->data = data;

   393   return 0;

   394 }