/*
** 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.
*/
#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.
*/
void sqlite3HashInit(Hash *pNew){
 assert( pNew!=0 );
 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;
 sqlite3_free(pH->ht);
 pH->ht = 0;
 pH->htsize = 0;
 while( elem ){
 HashElem *next_elem = elem->next;
 sqlite3_free(elem);
 elem = next_elem;
 }
 pH->count = 0;
}

/*
** The hashing function.
*/
static unsigned int strHash(const char *z){
 unsigned int h = 0;
 unsigned char c;
 while( (c = (unsigned char)*z++)!=0 ){ /*OPTIMIZATION-IF-TRUE*/
 /* Knuth multiplicative hashing. (Sorting & Searching, p. 510).
 ** 0x9e3779b1 is 2654435761 which is the closest prime number to
 ** (2**32)*golden_ratio, where golden_ratio = (sqrt(5) - 1)/2. */
 h += sqlite3UpperToLower[c];
 h *= 0x9e3779b1;
 }
 return h;
}


/* Link pNew element into the hash table pH. If pEntry!=0 then also
** insert pNew into the pEntry hash bucket.
*/
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 */
 if( pEntry ){
 pHead = pEntry->count ? pEntry->chain : 0;
 pEntry->count++;
 pEntry->chain = pNew;
 }else{
 pHead = 0;
 }
 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;
 }
}


/* Resize the hash table so that it contains "new_size" buckets.
**
** The hash table might fail to resize if sqlite3_malloc() fails or
** if the new size is the same as the prior size.
** Return TRUE if the resize occurs and false if not.
*/
static int rehash(Hash *pH, unsigned int new_size){
 struct _ht *new_ht; /* The new hash table */
 HashElem *elem, *next_elem; /* For looping over existing elements */

#if SQLITE_MALLOC_SOFT_LIMIT>0
 if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){
 new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht);
 }
 if( new_size==pH->htsize ) return 0;
#endif

 /* The inability to allocates space for a larger hash table is
 ** a performance hit but it is not a fatal error. So mark the
 ** allocation as a benign. Use sqlite3Malloc()/memset(0) instead of 
 ** sqlite3MallocZero() to make the allocation, as sqlite3MallocZero()
 ** only zeroes the requested number of bytes whereas this module will
 ** use the actual amount of space allocated for the hash table (which
 ** may be larger than the requested amount).
 */
 sqlite3BeginBenignMalloc();
 new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );
 sqlite3EndBenignMalloc();

 if( new_ht==0 ) return 0;
 sqlite3_free(pH->ht);
 pH->ht = new_ht;
 pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht);
 memset(new_ht, 0, new_size*sizeof(struct _ht));
 for(elem=pH->first, pH->first=0; elem; elem = next_elem){
 unsigned int h = strHash(elem->pKey) % new_size;
 next_elem = elem->next;
 insertElement(pH, &new_ht[h], elem);
 }
 return 1;
}

/* This function (for internal use only) locates an element in an
** hash table that matches the given key. If no element is found,
** a pointer to a static null element with HashElem.data==0 is returned.
** If pH is not NULL, then the hash for this key is written to *pH.
*/
static HashElem *findElementWithHash(
 const Hash *pH, /* The pH to be searched */
 const char *pKey, /* The key we are searching for */
 unsigned int *pHash /* Write the hash value here */
){
 HashElem *elem; /* Used to loop thru the element list */
 unsigned int count; /* Number of elements left to test */
 unsigned int h; /* The computed hash */
 static HashElem nullElement = { 0, 0, 0, 0 };

 if( pH->ht ){ /*OPTIMIZATION-IF-TRUE*/
 struct _ht *pEntry;
 h = strHash(pKey) % pH->htsize;
 pEntry = &pH->ht[h];
 elem = pEntry->chain;
 count = pEntry->count;
 }else{
 h = 0;
 elem = pH->first;
 count = pH->count;
 }
 if( pHash ) *pHash = h;
 while( count ){
 assert( elem!=0 );
 if( sqlite3StrICmp(elem->pKey,pKey)==0 ){ 
 return elem;
 }
 elem = elem->next;
 count--;
 }
 return &nullElement;
}

/* 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 */
 unsigned 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;
 }
 if( pH->ht ){
 pEntry = &pH->ht[h];
 if( pEntry->chain==elem ){
 pEntry->chain = elem->next;
 }
 assert( pEntry->count>0 );
 pEntry->count--;
 }
 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. Return the data for this element if it is
** found, or NULL if there is no match.
*/
void *sqlite3HashFind(const Hash *pH, const char *pKey){
 assert( pH!=0 );
 assert( pKey!=0 );
 return findElementWithHash(pH, pKey, 0)->data;
}

/* Insert an element into the hash table pH. The key is pKey
** and the data is "data".
**
** If no element exists with a matching key, then a new
** element is created and 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 char *pKey, void *data){
 unsigned 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 */

 assert( pH!=0 );
 assert( pKey!=0 );
 elem = findElementWithHash(pH,pKey,&h);
 if( elem->data ){
 void *old_data = elem->data;
 if( data==0 ){
 removeElementGivenHash(pH,elem,h);
 }else{
 elem->data = data;
 elem->pKey = pKey;
 }
 return old_data;
 }
 if( data==0 ) return 0;
 new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );
 if( new_elem==0 ) return data;
 new_elem->pKey = pKey;
 new_elem->data = data;
 pH->count++;
 if( pH->count>=10 && pH->count > 2*pH->htsize ){
 if( rehash(pH, pH->count*2) ){
 assert( pH->htsize>0 );
 h = strHash(pKey) % pH->htsize;
 }
 }
 insertElement(pH, pH->ht ? &pH->ht[h] : 0, new_elem);
 return 0;
}