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hash.c
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00001 /*
00002 ** 2001 September 22
00003 **
00004 ** The author disclaims copyright to this source code.  In place of
00005 ** a legal notice, here is a blessing:
00006 **
00007 **    May you do good and not evil.
00008 **    May you find forgiveness for yourself and forgive others.
00009 **    May you share freely, never taking more than you give.
00010 **
00011 *************************************************************************
00012 ** This is the implementation of generic hash-tables
00013 ** used in SQLite.
00014 **
00015 ** $Id: hash.c 195361 2005-09-07 15:11:33Z iliaa $
00016 */
00017 #include "sqliteInt.h"
00018 #include <assert.h>
00019 
00020 /* Turn bulk memory into a hash table object by initializing the
00021 ** fields of the Hash structure.
00022 **
00023 ** "new" is a pointer to the hash table that is to be initialized.
00024 ** keyClass is one of the constants SQLITE_HASH_INT, SQLITE_HASH_POINTER,
00025 ** SQLITE_HASH_BINARY, or SQLITE_HASH_STRING.  The value of keyClass 
00026 ** determines what kind of key the hash table will use.  "copyKey" is
00027 ** true if the hash table should make its own private copy of keys and
00028 ** false if it should just use the supplied pointer.  CopyKey only makes
00029 ** sense for SQLITE_HASH_STRING and SQLITE_HASH_BINARY and is ignored
00030 ** for other key classes.
00031 */
00032 void sqliteHashInit(Hash *new, int keyClass, int copyKey){
00033   assert( new!=0 );
00034   assert( keyClass>=SQLITE_HASH_INT && keyClass<=SQLITE_HASH_BINARY );
00035   new->keyClass = keyClass;
00036   new->copyKey = copyKey &&
00037                 (keyClass==SQLITE_HASH_STRING || keyClass==SQLITE_HASH_BINARY);
00038   new->first = 0;
00039   new->count = 0;
00040   new->htsize = 0;
00041   new->ht = 0;
00042 }
00043 
00044 /* Remove all entries from a hash table.  Reclaim all memory.
00045 ** Call this routine to delete a hash table or to reset a hash table
00046 ** to the empty state.
00047 */
00048 void sqliteHashClear(Hash *pH){
00049   HashElem *elem;         /* For looping over all elements of the table */
00050 
00051   assert( pH!=0 );
00052   elem = pH->first;
00053   pH->first = 0;
00054   if( pH->ht ) sqliteFree(pH->ht);
00055   pH->ht = 0;
00056   pH->htsize = 0;
00057   while( elem ){
00058     HashElem *next_elem = elem->next;
00059     if( pH->copyKey && elem->pKey ){
00060       sqliteFree(elem->pKey);
00061     }
00062     sqliteFree(elem);
00063     elem = next_elem;
00064   }
00065   pH->count = 0;
00066 }
00067 
00068 /*
00069 ** Hash and comparison functions when the mode is SQLITE_HASH_INT
00070 */
00071 static int intHash(const void *pKey, int nKey){
00072   return nKey ^ (nKey<<8) ^ (nKey>>8);
00073 }
00074 static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){
00075   return n2 - n1;
00076 }
00077 
00078 #if 0 /* NOT USED */
00079 /*
00080 ** Hash and comparison functions when the mode is SQLITE_HASH_POINTER
00081 */
00082 static int ptrHash(const void *pKey, int nKey){
00083   uptr x = Addr(pKey);
00084   return x ^ (x<<8) ^ (x>>8);
00085 }
00086 static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){
00087   if( pKey1==pKey2 ) return 0;
00088   if( pKey1<pKey2 ) return -1;
00089   return 1;
00090 }
00091 #endif
00092 
00093 /*
00094 ** Hash and comparison functions when the mode is SQLITE_HASH_STRING
00095 */
00096 static int strHash(const void *pKey, int nKey){
00097   return sqliteHashNoCase((const char*)pKey, nKey); 
00098 }
00099 static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
00100   if( n1!=n2 ) return n2-n1;
00101   return sqliteStrNICmp((const char*)pKey1,(const char*)pKey2,n1);
00102 }
00103 
00104 /*
00105 ** Hash and comparison functions when the mode is SQLITE_HASH_BINARY
00106 */
00107 static int binHash(const void *pKey, int nKey){
00108   int h = 0;
00109   const char *z = (const char *)pKey;
00110   while( nKey-- > 0 ){
00111     h = (h<<3) ^ h ^ *(z++);
00112   }
00113   return h & 0x7fffffff;
00114 }
00115 static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
00116   if( n1!=n2 ) return n2-n1;
00117   return memcmp(pKey1,pKey2,n1);
00118 }
00119 
00120 /*
00121 ** Return a pointer to the appropriate hash function given the key class.
00122 **
00123 ** The C syntax in this function definition may be unfamilar to some 
00124 ** programmers, so we provide the following additional explanation:
00125 **
00126 ** The name of the function is "hashFunction".  The function takes a
00127 ** single parameter "keyClass".  The return value of hashFunction()
00128 ** is a pointer to another function.  Specifically, the return value
00129 ** of hashFunction() is a pointer to a function that takes two parameters
00130 ** with types "const void*" and "int" and returns an "int".
00131 */
00132 static int (*hashFunction(int keyClass))(const void*,int){
00133   switch( keyClass ){
00134     case SQLITE_HASH_INT:     return &intHash;
00135     /* case SQLITE_HASH_POINTER: return &ptrHash; // NOT USED */
00136     case SQLITE_HASH_STRING:  return &strHash;
00137     case SQLITE_HASH_BINARY:  return &binHash;;
00138     default: break;
00139   }
00140   return 0;
00141 }
00142 
00143 /*
00144 ** Return a pointer to the appropriate hash function given the key class.
00145 **
00146 ** For help in interpreted the obscure C code in the function definition,
00147 ** see the header comment on the previous function.
00148 */
00149 static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
00150   switch( keyClass ){
00151     case SQLITE_HASH_INT:     return &intCompare;
00152     /* case SQLITE_HASH_POINTER: return &ptrCompare; // NOT USED */
00153     case SQLITE_HASH_STRING:  return &strCompare;
00154     case SQLITE_HASH_BINARY:  return &binCompare;
00155     default: break;
00156   }
00157   return 0;
00158 }
00159 
00160 
00161 /* Resize the hash table so that it cantains "new_size" buckets.
00162 ** "new_size" must be a power of 2.  The hash table might fail 
00163 ** to resize if sqliteMalloc() fails.
00164 */
00165 static void rehash(Hash *pH, int new_size){
00166   struct _ht *new_ht;            /* The new hash table */
00167   HashElem *elem, *next_elem;    /* For looping over existing elements */
00168   HashElem *x;                   /* Element being copied to new hash table */
00169   int (*xHash)(const void*,int); /* The hash function */
00170 
00171   assert( (new_size & (new_size-1))==0 );
00172   new_ht = (struct _ht *)sqliteMalloc( new_size*sizeof(struct _ht) );
00173   if( new_ht==0 ) return;
00174   if( pH->ht ) sqliteFree(pH->ht);
00175   pH->ht = new_ht;
00176   pH->htsize = new_size;
00177   xHash = hashFunction(pH->keyClass);
00178   for(elem=pH->first, pH->first=0; elem; elem = next_elem){
00179     int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
00180     next_elem = elem->next;
00181     x = new_ht[h].chain;
00182     if( x ){
00183       elem->next = x;
00184       elem->prev = x->prev;
00185       if( x->prev ) x->prev->next = elem;
00186       else          pH->first = elem;
00187       x->prev = elem;
00188     }else{
00189       elem->next = pH->first;
00190       if( pH->first ) pH->first->prev = elem;
00191       elem->prev = 0;
00192       pH->first = elem;
00193     }
00194     new_ht[h].chain = elem;
00195     new_ht[h].count++;
00196   }
00197 }
00198 
00199 /* This function (for internal use only) locates an element in an
00200 ** hash table that matches the given key.  The hash for this key has
00201 ** already been computed and is passed as the 4th parameter.
00202 */
00203 static HashElem *findElementGivenHash(
00204   const Hash *pH,     /* The pH to be searched */
00205   const void *pKey,   /* The key we are searching for */
00206   int nKey,
00207   int h               /* The hash for this key. */
00208 ){
00209   HashElem *elem;                /* Used to loop thru the element list */
00210   int count;                     /* Number of elements left to test */
00211   int (*xCompare)(const void*,int,const void*,int);  /* comparison function */
00212 
00213   if( pH->ht ){
00214     elem = pH->ht[h].chain;
00215     count = pH->ht[h].count;
00216     xCompare = compareFunction(pH->keyClass);
00217     while( count-- && elem ){
00218       if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){ 
00219         return elem;
00220       }
00221       elem = elem->next;
00222     }
00223   }
00224   return 0;
00225 }
00226 
00227 /* Remove a single entry from the hash table given a pointer to that
00228 ** element and a hash on the element's key.
00229 */
00230 static void removeElementGivenHash(
00231   Hash *pH,         /* The pH containing "elem" */
00232   HashElem* elem,   /* The element to be removed from the pH */
00233   int h             /* Hash value for the element */
00234 ){
00235   if( elem->prev ){
00236     elem->prev->next = elem->next; 
00237   }else{
00238     pH->first = elem->next;
00239   }
00240   if( elem->next ){
00241     elem->next->prev = elem->prev;
00242   }
00243   if( pH->ht[h].chain==elem ){
00244     pH->ht[h].chain = elem->next;
00245   }
00246   pH->ht[h].count--;
00247   if( pH->ht[h].count<=0 ){
00248     pH->ht[h].chain = 0;
00249   }
00250   if( pH->copyKey && elem->pKey ){
00251     sqliteFree(elem->pKey);
00252   }
00253   sqliteFree( elem );
00254   pH->count--;
00255 }
00256 
00257 /* Attempt to locate an element of the hash table pH with a key
00258 ** that matches pKey,nKey.  Return the data for this element if it is
00259 ** found, or NULL if there is no match.
00260 */
00261 void *sqliteHashFind(const Hash *pH, const void *pKey, int nKey){
00262   int h;             /* A hash on key */
00263   HashElem *elem;    /* The element that matches key */
00264   int (*xHash)(const void*,int);  /* The hash function */
00265 
00266   if( pH==0 || pH->ht==0 ) return 0;
00267   xHash = hashFunction(pH->keyClass);
00268   assert( xHash!=0 );
00269   h = (*xHash)(pKey,nKey);
00270   assert( (pH->htsize & (pH->htsize-1))==0 );
00271   elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
00272   return elem ? elem->data : 0;
00273 }
00274 
00275 /* Insert an element into the hash table pH.  The key is pKey,nKey
00276 ** and the data is "data".
00277 **
00278 ** If no element exists with a matching key, then a new
00279 ** element is created.  A copy of the key is made if the copyKey
00280 ** flag is set.  NULL is returned.
00281 **
00282 ** If another element already exists with the same key, then the
00283 ** new data replaces the old data and the old data is returned.
00284 ** The key is not copied in this instance.  If a malloc fails, then
00285 ** the new data is returned and the hash table is unchanged.
00286 **
00287 ** If the "data" parameter to this function is NULL, then the
00288 ** element corresponding to "key" is removed from the hash table.
00289 */
00290 void *sqliteHashInsert(Hash *pH, const void *pKey, int nKey, void *data){
00291   int hraw;             /* Raw hash value of the key */
00292   int h;                /* the hash of the key modulo hash table size */
00293   HashElem *elem;       /* Used to loop thru the element list */
00294   HashElem *new_elem;   /* New element added to the pH */
00295   int (*xHash)(const void*,int);  /* The hash function */
00296 
00297   assert( pH!=0 );
00298   xHash = hashFunction(pH->keyClass);
00299   assert( xHash!=0 );
00300   hraw = (*xHash)(pKey, nKey);
00301   assert( (pH->htsize & (pH->htsize-1))==0 );
00302   h = hraw & (pH->htsize-1);
00303   elem = findElementGivenHash(pH,pKey,nKey,h);
00304   if( elem ){
00305     void *old_data = elem->data;
00306     if( data==0 ){
00307       removeElementGivenHash(pH,elem,h);
00308     }else{
00309       elem->data = data;
00310     }
00311     return old_data;
00312   }
00313   if( data==0 ) return 0;
00314   new_elem = (HashElem*)sqliteMalloc( sizeof(HashElem) );
00315   if( new_elem==0 ) return data;
00316   if( pH->copyKey && pKey!=0 ){
00317     new_elem->pKey = sqliteMallocRaw( nKey );
00318     if( new_elem->pKey==0 ){
00319       sqliteFree(new_elem);
00320       return data;
00321     }
00322     memcpy((void*)new_elem->pKey, pKey, nKey);
00323   }else{
00324     new_elem->pKey = (void*)pKey;
00325   }
00326   new_elem->nKey = nKey;
00327   pH->count++;
00328   if( pH->htsize==0 ) rehash(pH,8);
00329   if( pH->htsize==0 ){
00330     pH->count = 0;
00331     sqliteFree(new_elem);
00332     return data;
00333   }
00334   if( pH->count > pH->htsize ){
00335     rehash(pH,pH->htsize*2);
00336   }
00337   assert( (pH->htsize & (pH->htsize-1))==0 );
00338   h = hraw & (pH->htsize-1);
00339   elem = pH->ht[h].chain;
00340   if( elem ){
00341     new_elem->next = elem;
00342     new_elem->prev = elem->prev;
00343     if( elem->prev ){ elem->prev->next = new_elem; }
00344     else            { pH->first = new_elem; }
00345     elem->prev = new_elem;
00346   }else{
00347     new_elem->next = pH->first;
00348     new_elem->prev = 0;
00349     if( pH->first ){ pH->first->prev = new_elem; }
00350     pH->first = new_elem;
00351   }
00352   pH->ht[h].count++;
00353   pH->ht[h].chain = new_elem;
00354   new_elem->data = data;
00355   return 0;
00356 }