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DEFINITIONS
This source file includes following definitions.
- sqliteHashInit
- sqliteHashClear
- intHash
- intCompare
- ptrHash
- ptrCompare
- strHash
- strCompare
- binHash
- binCompare
- hashFunction
- compareFunction
- rehash
- findElementGivenHash
- removeElementGivenHash
- sqliteHashFind
- sqliteHashInsert
/*
** 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: hash.c,v 1.6.4.1 2005/09/07 15:11:32 iliaa Exp $
*/
#include "sqliteInt.h"
#include <assert.h>
/* Turn bulk memory into a hash table object by initializing the
** fields of the Hash structure.
**
** "new" 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 sqliteHashInit(Hash *new, int keyClass, int copyKey){
assert( new!=0 );
assert( keyClass>=SQLITE_HASH_INT && keyClass<=SQLITE_HASH_BINARY );
new->keyClass = keyClass;
new->copyKey = copyKey &&
(keyClass==SQLITE_HASH_STRING || keyClass==SQLITE_HASH_BINARY);
new->first = 0;
new->count = 0;
new->htsize = 0;
new->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 sqliteHashClear(Hash *pH){
HashElem *elem; /* For looping over all elements of the table */
assert( pH!=0 );
elem = pH->first;
pH->first = 0;
if( pH->ht ) sqliteFree(pH->ht);
pH->ht = 0;
pH->htsize = 0;
while( elem ){
HashElem *next_elem = elem->next;
if( pH->copyKey && elem->pKey ){
sqliteFree(elem->pKey);
}
sqliteFree(elem);
elem = next_elem;
}
pH->count = 0;
}
/*
** 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;
}
#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){
return sqliteHashNoCase((const char*)pKey, nKey);
}
static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
if( n1!=n2 ) return n2-n1;
return sqliteStrNICmp((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 n2-n1;
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){
switch( keyClass ){
case SQLITE_HASH_INT: return &intHash;
/* case SQLITE_HASH_POINTER: return &ptrHash; // NOT USED */
case SQLITE_HASH_STRING: return &strHash;
case SQLITE_HASH_BINARY: return &binHash;;
default: break;
}
return 0;
}
/*
** 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){
switch( keyClass ){
case SQLITE_HASH_INT: return &intCompare;
/* case SQLITE_HASH_POINTER: return &ptrCompare; // NOT USED */
case SQLITE_HASH_STRING: return &strCompare;
case SQLITE_HASH_BINARY: return &binCompare;
default: break;
}
return 0;
}
/* 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 sqliteMalloc() 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 */
HashElem *x; /* Element being copied to new hash table */
int (*xHash)(const void*,int); /* The hash function */
assert( (new_size & (new_size-1))==0 );
new_ht = (struct _ht *)sqliteMalloc( new_size*sizeof(struct _ht) );
if( new_ht==0 ) return;
if( pH->ht ) sqliteFree(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;
x = new_ht[h].chain;
if( x ){
elem->next = x;
elem->prev = x->prev;
if( x->prev ) x->prev->next = elem;
else pH->first = elem;
x->prev = elem;
}else{
elem->next = pH->first;
if( pH->first ) pH->first->prev = elem;
elem->prev = 0;
pH->first = elem;
}
new_ht[h].chain = elem;
new_ht[h].count++;
}
}
/* 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 ){
elem = pH->ht[h].chain;
count = pH->ht[h].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 */
){
if( elem->prev ){
elem->prev->next = elem->next;
}else{
pH->first = elem->next;
}
if( elem->next ){
elem->next->prev = elem->prev;
}
if( pH->ht[h].chain==elem ){
pH->ht[h].chain = elem->next;
}
pH->ht[h].count--;
if( pH->ht[h].count<=0 ){
pH->ht[h].chain = 0;
}
if( pH->copyKey && elem->pKey ){
sqliteFree(elem->pKey);
}
sqliteFree( elem );
pH->count--;
}
/* 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 *sqliteHashFind(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 ? 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 *sqliteHashInsert(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;
}
return old_data;
}
if( data==0 ) return 0;
new_elem = (HashElem*)sqliteMalloc( sizeof(HashElem) );
if( new_elem==0 ) return data;
if( pH->copyKey && pKey!=0 ){
new_elem->pKey = sqliteMallocRaw( nKey );
if( new_elem->pKey==0 ){
sqliteFree(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;
sqliteFree(new_elem);
return data;
}
if( pH->count > pH->htsize ){
rehash(pH,pH->htsize*2);
}
assert( (pH->htsize & (pH->htsize-1))==0 );
h = hraw & (pH->htsize-1);
elem = pH->ht[h].chain;
if( elem ){
new_elem->next = elem;
new_elem->prev = elem->prev;
if( elem->prev ){ elem->prev->next = new_elem; }
else { pH->first = new_elem; }
elem->prev = new_elem;
}else{
new_elem->next = pH->first;
new_elem->prev = 0;
if( pH->first ){ pH->first->prev = new_elem; }
pH->first = new_elem;
}
pH->ht[h].count++;
pH->ht[h].chain = new_elem;
new_elem->data = data;
return 0;
}