Simplifications to the symbol table implementation in hash.c. For very small
symbol tables (less than 10 entries) a simple linked list is used instead
of a hash table. Number of hash table buckets is limited to prevent large
allocations. (CVS 6559)
FossilOrigin-Name: 5c737835dec9e6038b304c198aa14337a6f23c1c
diff --git a/src/hash.c b/src/hash.c
index 3761fb5..9d9be94 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -12,7 +12,7 @@
** This is the implementation of generic hash-tables
** used in SQLite.
**
-** $Id: hash.c,v 1.34 2009/04/28 13:01:09 drh Exp $
+** $Id: hash.c,v 1.35 2009/04/28 15:43:45 drh Exp $
*/
#include "sqliteInt.h"
#include <assert.h>
@@ -60,7 +60,7 @@
/*
** Hash and comparison functions when the mode is SQLITE_HASH_STRING
*/
-static int strHash(const void *pKey, int nKey){
+static unsigned int strHash(const void *pKey, int nKey){
const char *z = (const char *)pKey;
int h = 0;
assert( nKey>0 );
@@ -68,7 +68,7 @@
h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++];
nKey--;
}
- return h & 0x7fffffff;
+ return h;
}
static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
if( n1!=n2 ) return 1;
@@ -76,7 +76,8 @@
}
-/* Link an element into the hash table
+/* 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 */
@@ -84,7 +85,13 @@
HashElem *pNew /* The element to be inserted */
){
HashElem *pHead; /* First element already in pEntry */
- pHead = pEntry->chain;
+ 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;
@@ -97,44 +104,45 @@
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.
+**
+** 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 void rehash(Hash *pH, int new_size){
+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 */
-#ifdef SQLITE_MALLOC_SOFT_LIMIT
+#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;
+ if( new_size==pH->htsize ) return 0;
#endif
- /* 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).
+ /* 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.
*/
- if( pH->htsize>0 ) sqlite3BeginBenignMalloc();
- new_ht = (struct _ht *)sqlite3MallocZero( new_size*sizeof(struct _ht) );
- if( pH->htsize>0 ) sqlite3EndBenignMalloc();
+ sqlite3BeginBenignMalloc();
+ new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );
+ sqlite3EndBenignMalloc();
- if( new_ht==0 ) return;
+ if( new_ht==0 ) return 0;
sqlite3_free(pH->ht);
pH->ht = new_ht;
- pH->htsize = new_size;
+ 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){
- int h = strHash(elem->pKey, elem->nKey) & (new_size-1);
+ unsigned int h = strHash(elem->pKey, elem->nKey) % 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
@@ -144,8 +152,8 @@
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. */
+ int nKey, /* Bytes in key (not counting zero terminator) */
+ unsigned int h /* The hash for this key. */
){
HashElem *elem; /* Used to loop thru the element list */
int count; /* Number of elements left to test */
@@ -154,12 +162,15 @@
struct _ht *pEntry = &pH->ht[h];
elem = pEntry->chain;
count = pEntry->count;
- while( count-- && elem ){
- if( strCompare(elem->pKey,elem->nKey,pKey,nKey)==0 ){
- return elem;
- }
- elem = elem->next;
+ }else{
+ elem = pH->first;
+ count = pH->count;
+ }
+ while( count-- && ALWAYS(elem) ){
+ if( strCompare(elem->pKey,elem->nKey,pKey,nKey)==0 ){
+ return elem;
}
+ elem = elem->next;
}
return 0;
}
@@ -170,7 +181,7 @@
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 */
+ unsigned int h /* Hash value for the element */
){
struct _ht *pEntry;
if( elem->prev ){
@@ -181,13 +192,13 @@
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->ht ){
+ pEntry = &pH->ht[h];
+ if( pEntry->chain==elem ){
+ pEntry->chain = elem->next;
+ }
+ pEntry->count--;
+ assert( pEntry->count>=0 );
}
if( pH->copyKey ){
sqlite3_free(elem->pKey);
@@ -202,27 +213,22 @@
}
/* 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 */
-
- if( pH==0 || pH->ht==0 ) return 0;
- h = strHash(pKey,nKey);
- elem = findElementGivenHash(pH,pKey,nKey, h % pH->htsize);
- 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);
+ unsigned int h; /* A hash on key */
+
+ assert( pH!=0 );
+ assert( pKey!=0 );
+ assert( nKey>0 );
+ if( pH->ht ){
+ h = strHash(pKey, nKey) % pH->htsize;
+ }else{
+ h = 0;
+ }
+ elem = findElementGivenHash(pH, pKey, nKey, h);
return elem ? elem->data : 0;
}
@@ -242,34 +248,36 @@
** 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 */
+ 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 );
- hraw = strHash(pKey, nKey);
+ assert( pKey!=0 );
+ assert( nKey>0 );
if( pH->htsize ){
- h = hraw % pH->htsize;
- 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);
+ h = strHash(pKey, nKey) % pH->htsize;
+ }else{
+ h = 0;
+ }
+ 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;
}
- return old_data;
+ assert(nKey==elem->nKey);
}
+ return old_data;
}
if( data==0 ) return 0;
new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );
if( new_elem==0 ) return data;
- if( pH->copyKey && pKey!=0 ){
+ if( pH->copyKey ){
new_elem->pKey = sqlite3Malloc( nKey );
if( new_elem->pKey==0 ){
sqlite3_free(new_elem);
@@ -280,24 +288,17 @@
new_elem->pKey = (void*)pKey;
}
new_elem->nKey = nKey;
+ new_elem->data = data;
pH->count++;
- if( pH->htsize==0 ){
- rehash(pH, 128/sizeof(pH->ht[0]));
- if( pH->htsize==0 ){
- pH->count = 0;
- if( pH->copyKey ){
- sqlite3_free(new_elem->pKey);
- }
- sqlite3_free(new_elem);
- return data;
+ if( pH->count>=10 && pH->count > 2*pH->htsize ){
+ if( rehash(pH, pH->count*2) && pH->htsize ){
+ h = strHash(pKey, nKey) % pH->htsize;
}
}
- if( pH->count > pH->htsize ){
- rehash(pH,pH->htsize*2);
+ if( pH->ht ){
+ insertElement(pH, &pH->ht[h], new_elem);
+ }else{
+ insertElement(pH, 0, new_elem);
}
- assert( pH->htsize>0 );
- h = hraw % pH->htsize;
- insertElement(pH, &pH->ht[h], new_elem);
- new_elem->data = data;
return 0;
}
diff --git a/src/hash.h b/src/hash.h
index 16b391f..1e3b9a0 100644
--- a/src/hash.h
+++ b/src/hash.h
@@ -12,7 +12,7 @@
** This is the header file for the generic hash-table implemenation
** used in SQLite.
**
-** $Id: hash.h,v 1.12 2008/10/10 17:41:29 drh Exp $
+** $Id: hash.h,v 1.13 2009/04/28 15:43:45 drh Exp $
*/
#ifndef _SQLITE_HASH_H_
#define _SQLITE_HASH_H_
@@ -25,12 +25,25 @@
** The internals of this structure are intended to be opaque -- client
** code should not attempt to access or modify the fields of this structure
** directly. Change this structure only by using the routines below.
-** However, many of the "procedures" and "functions" for modifying and
+** However, some of the "procedures" and "functions" for modifying and
** accessing this structure are really macros, so we can't really make
** this structure opaque.
+**
+** All elements of the hash table are on a single doubly-linked list.
+** Hash.first points to the head of this list.
+**
+** There are Hash.htsize buckets. Each bucket points to a spot in
+** the global doubly-linked list. The contents of the bucket are the
+** element pointed to plus the next _ht.count-1 elements in the list.
+**
+** Hash.htsize and Hash.ht may be zero. In that case lookup is done
+** by a linear search of the global list. For small tables, the
+** Hash.ht table is never allocated because if there are few elements
+** in the table, it is faster to do a linear search than to manage
+** the hash table.
*/
struct Hash {
- unsigned int copyKey: 1; /* True if copy of key made on insert */
+ unsigned int copyKey : 1; /* True if copy of key made on insert */
unsigned int htsize : 31; /* Number of buckets in the hash table */
unsigned int count; /* Number of entries in this table */
HashElem *first; /* The first element of the array */
@@ -76,12 +89,12 @@
#define sqliteHashFirst(H) ((H)->first)
#define sqliteHashNext(E) ((E)->next)
#define sqliteHashData(E) ((E)->data)
-#define sqliteHashKey(E) ((E)->pKey)
-#define sqliteHashKeysize(E) ((E)->nKey)
+/* #define sqliteHashKey(E) ((E)->pKey) // NOT USED */
+/* #define sqliteHashKeysize(E) ((E)->nKey) // NOT USED */
/*
** Number of entries in a hash table
*/
-#define sqliteHashCount(H) ((H)->count)
+/* #define sqliteHashCount(H) ((H)->count) // NOT USED */
#endif /* _SQLITE_HASH_H_ */
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index c312475..e2b451b 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -11,7 +11,7 @@
*************************************************************************
** Internal interface definitions for SQLite.
**
-** @(#) $Id: sqliteInt.h,v 1.861 2009/04/24 15:46:22 drh Exp $
+** @(#) $Id: sqliteInt.h,v 1.862 2009/04/28 15:43:45 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_
@@ -145,10 +145,10 @@
#endif
/*
-** If SQLITE_MALLOC_SOFT_LIMIT is defined, then try to keep the
+** If SQLITE_MALLOC_SOFT_LIMIT is not zero, then try to keep the
** sizes of memory allocations below this value where possible.
*/
-#if defined(SQLITE_POW2_MEMORY_SIZE) && !defined(SQLITE_MALLOC_SOFT_LIMIT)
+#if !defined(SQLITE_MALLOC_SOFT_LIMIT)
# define SQLITE_MALLOC_SOFT_LIMIT 1024
#endif