/*

 ** 2001 September 22

 **

 ** The author disclaims copyright to this source code.  In place of

 ** a legal notice, here is a blessing:

 **

 **    May you do good and not evil.

 **    May you find forgiveness for yourself and forgive others.

 **    May you share freely, never taking more than you give.

 **

 *************************************************************************

 ** This is the implementation of generic hash-tables

 ** used in SQLite.

 **

 ** $Id$

 */

 #include "sqliteInt.h"

 #include <assert.h>

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

 ** fields of the Hash structure.

 **

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

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

 ** SQLITE_HASH_BINARY, or SQLITE_HASH_STRING.  The value of keyClass 

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

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

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

 ** sense for SQLITE_HASH_STRING and SQLITE_HASH_BINARY and is ignored

 ** for other key classes.

 */

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

   assert( pNew!=0 );

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

   pNew->keyClass = keyClass;

 #if 0

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

 #endif

   pNew->copyKey = copyKey;

   pNew->first = 0;

   pNew->count = 0;

   pNew->htsize = 0;

   pNew->ht = 0;

 }

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

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

 ** to the empty state.

 */

 void sqlite3HashClear(Hash *pH){

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

   assert( pH!=0 );

   elem = pH->first;

   pH->first = 0;

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

   pH->ht = 0;

   pH->htsize = 0;

   while( elem ){

     HashElem *next_elem = elem->next;

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

       sqlite3_free(elem->pKey);

     }

     sqlite3_free(elem);

     elem = next_elem;

   }

   pH->count = 0;

 }

 #if 0 /* NOT USED */

 /*

 ** Hash and comparison functions when the mode is SQLITE_HASH_INT

 */

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

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

 }

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

   return n2 - n1;

 }

 #endif

 #if 0 /* NOT USED */

 /*

 ** Hash and comparison functions when the mode is SQLITE_HASH_POINTER

 */

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

   uptr x = Addr(pKey);

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

 }

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

   if( pKey1==pKey2 ) return 0;

   if( pKey1<pKey2 ) return -1;

   return 1;

 }

 #endif

 /*

 ** Hash and comparison functions when the mode is SQLITE_HASH_STRING

 */

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

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

   int h = 0;

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

   while( nKey > 0  ){

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

     nKey--;

   }

   return h & 0x7fffffff;

 }

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

   if( n1!=n2 ) return 1;

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

 }

 /*

 ** Hash and comparison functions when the mode is SQLITE_HASH_BINARY

 */

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

   int h = 0;

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

   while( nKey-- > 0 ){

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

   }

   return h & 0x7fffffff;

 }

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

   if( n1!=n2 ) return 1;

   return memcmp(pKey1,pKey2,n1);

 }

 /*

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

 **

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

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

 **

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

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

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

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

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

 */

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

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

   switch( keyClass ){

     case SQLITE_HASH_INT:     return &intHash;

     case SQLITE_HASH_POINTER: return &ptrHash;

     case SQLITE_HASH_STRING:  return &strHash;

     case SQLITE_HASH_BINARY:  return &binHash;;

     default: break;

   }

   return 0;

 #else

   if( keyClass==SQLITE_HASH_STRING ){

     return &strHash;

   }else{

     assert( keyClass==SQLITE_HASH_BINARY );

     return &binHash;

   }

 #endif

 }

 /*

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

 **

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

 ** see the header comment on the previous function.

 */

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

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

   switch( keyClass ){

     case SQLITE_HASH_INT:     return &intCompare;

     case SQLITE_HASH_POINTER: return &ptrCompare;

     case SQLITE_HASH_STRING:  return &strCompare;

     case SQLITE_HASH_BINARY:  return &binCompare;

     default: break;

   }

   return 0;

 #else

   if( keyClass==SQLITE_HASH_STRING ){

     return &strCompare;

   }else{

     assert( keyClass==SQLITE_HASH_BINARY );

     return &binCompare;

   }

 #endif

 }

 /* Link an element into the hash table

 */

 static void insertElement(

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

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

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

 ){

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

   pHead = pEntry->chain;

   if( pHead ){

     pNew->next = pHead;

     pNew->prev = pHead->prev;

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

     else             { pH->first = pNew; }

     pHead->prev = pNew;

   }else{

     pNew->next = pH->first;

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

     pNew->prev = 0;

     pH->first = pNew;

   }

   pEntry->count++;

   pEntry->chain = pNew;

 }

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

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

 ** to resize if sqlite3_malloc() fails.

 */

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

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

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

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

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

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

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

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

   ** hit only, not a fatal error).

   */

   sqlite3MallocBenignFailure(pH->htsize>0);

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

   if( new_ht==0 ) return;

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

   pH->ht = new_ht;

   pH->htsize = new_size;

   xHash = hashFunction(pH->keyClass);

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

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

     next_elem = elem->next;

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

   }

 }

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

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

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

 */

 static HashElem *findElementGivenHash(

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

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

   int nKey,

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

 ){

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

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

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

   if( pH->ht ){

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

     elem = pEntry->chain;

     count = pEntry->count;

     xCompare = compareFunction(pH->keyClass);

     while( count-- && elem ){

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

         return elem;

       }

       elem = elem->next;

     }

   }

   return 0;

 }

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

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

 */

 static void removeElementGivenHash(

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

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

   int h             /* Hash value for the element */

 ){

   struct _ht *pEntry;

   if( elem->prev ){

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

   }else{

     pH->first = elem->next;

   }

   if( elem->next ){

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

   }

   pEntry = &pH->ht[h];

   if( pEntry->chain==elem ){

     pEntry->chain = elem->next;

   }

   pEntry->count--;

   if( pEntry->count<=0 ){

     pEntry->chain = 0;

   }

   if( pH->copyKey ){

     sqlite3_free(elem->pKey);

   }

   sqlite3_free( elem );

   pH->count--;

   if( pH->count<=0 ){

     assert( pH->first==0 );

     assert( pH->count==0 );

     sqlite3HashClear(pH);

   }

 }

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

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

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

 ** otherwise.

 */

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

   int h;             /* A hash on key */

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

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

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

   xHash = hashFunction(pH->keyClass);

   assert( xHash!=0 );

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

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

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

   return elem;

 }

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

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

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

 */

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

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

   elem = sqlite3HashFindElem(pH, pKey, nKey);

   return elem ? elem->data : 0;

 }

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

 ** and the data is "data".

 **

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

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

 ** flag is set.  NULL is returned.

 **

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

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

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

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

 **

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

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

 */

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

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

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

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

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

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

   assert( pH!=0 );

   xHash = hashFunction(pH->keyClass);

   assert( xHash!=0 );

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

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

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

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

   if( elem ){

     void *old_data = elem->data;

     if( data==0 ){

       removeElementGivenHash(pH,elem,h);

     }else{

       elem->data = data;

       if( !pH->copyKey ){

         elem->pKey = (void *)pKey;

       }

       assert(nKey==elem->nKey);

     }

     return old_data;

   }

   if( data==0 ) return 0;

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

   if( new_elem==0 ) return data;

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

     new_elem->pKey = sqlite3_malloc( nKey );

     if( new_elem->pKey==0 ){

       sqlite3_free(new_elem);

       return data;

     }

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

   }else{

     new_elem->pKey = (void*)pKey;

   }

   new_elem->nKey = nKey;

   pH->count++;

   if( pH->htsize==0 ){

     rehash(pH,8);

     if( pH->htsize==0 ){

       pH->count = 0;

       if( pH->copyKey ){

         sqlite3_free(new_elem->pKey);

       }

       sqlite3_free(new_elem);

       return data;

     }

   }

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

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

   }

   assert( pH->htsize>0 );

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

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

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

   new_elem->data = data;

   return 0;

 }