4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
7 ** May you do good and not evil.
8 ** May you find forgiveness for yourself and forgive others.
9 ** May you share freely, never taking more than you give.
11 *************************************************************************
12 ** This is the implementation of generic hash-tables
15 #include "sqliteInt.h"
18 /* Turn bulk memory into a hash table object by initializing the
19 ** fields of the Hash structure.
21 ** "pNew" is a pointer to the hash table that is to be initialized.
23 void sqlite3HashInit(Hash
*pNew
){
31 /* Remove all entries from a hash table. Reclaim all memory.
32 ** Call this routine to delete a hash table or to reset a hash table
33 ** to the empty state.
35 void sqlite3HashClear(Hash
*pH
){
36 HashElem
*elem
; /* For looping over all elements of the table */
45 HashElem
*next_elem
= elem
->next
;
53 ** The hashing function.
55 static unsigned int strHash(const char *z
){
58 while( (c
= (unsigned char)*z
++)!=0 ){ /*OPTIMIZATION-IF-TRUE*/
59 /* Knuth multiplicative hashing. (Sorting & Searching, p. 510).
60 ** 0x9e3779b1 is 2654435761 which is the closest prime number to
61 ** (2**32)*golden_ratio, where golden_ratio = (sqrt(5) - 1)/2. */
62 h
+= sqlite3UpperToLower
[c
];
69 /* Link pNew element into the hash table pH. If pEntry!=0 then also
70 ** insert pNew into the pEntry hash bucket.
72 static void insertElement(
73 Hash
*pH
, /* The complete hash table */
74 struct _ht
*pEntry
, /* The entry into which pNew is inserted */
75 HashElem
*pNew
/* The element to be inserted */
77 HashElem
*pHead
; /* First element already in pEntry */
79 pHead
= pEntry
->count
? pEntry
->chain
: 0;
87 pNew
->prev
= pHead
->prev
;
88 if( pHead
->prev
){ pHead
->prev
->next
= pNew
; }
89 else { pH
->first
= pNew
; }
92 pNew
->next
= pH
->first
;
93 if( pH
->first
){ pH
->first
->prev
= pNew
; }
100 /* Resize the hash table so that it contains "new_size" buckets.
102 ** The hash table might fail to resize if sqlite3_malloc() fails or
103 ** if the new size is the same as the prior size.
104 ** Return TRUE if the resize occurs and false if not.
106 static int rehash(Hash
*pH
, unsigned int new_size
){
107 struct _ht
*new_ht
; /* The new hash table */
108 HashElem
*elem
, *next_elem
; /* For looping over existing elements */
110 #if SQLITE_MALLOC_SOFT_LIMIT>0
111 if( new_size
*sizeof(struct _ht
)>SQLITE_MALLOC_SOFT_LIMIT
){
112 new_size
= SQLITE_MALLOC_SOFT_LIMIT
/sizeof(struct _ht
);
114 if( new_size
==pH
->htsize
) return 0;
117 /* The inability to allocates space for a larger hash table is
118 ** a performance hit but it is not a fatal error. So mark the
119 ** allocation as a benign. Use sqlite3Malloc()/memset(0) instead of
120 ** sqlite3MallocZero() to make the allocation, as sqlite3MallocZero()
121 ** only zeroes the requested number of bytes whereas this module will
122 ** use the actual amount of space allocated for the hash table (which
123 ** may be larger than the requested amount).
125 sqlite3BeginBenignMalloc();
126 new_ht
= (struct _ht
*)sqlite3Malloc( new_size
*sizeof(struct _ht
) );
127 sqlite3EndBenignMalloc();
129 if( new_ht
==0 ) return 0;
130 sqlite3_free(pH
->ht
);
132 pH
->htsize
= new_size
= sqlite3MallocSize(new_ht
)/sizeof(struct _ht
);
133 memset(new_ht
, 0, new_size
*sizeof(struct _ht
));
134 for(elem
=pH
->first
, pH
->first
=0; elem
; elem
= next_elem
){
135 unsigned int h
= strHash(elem
->pKey
) % new_size
;
136 next_elem
= elem
->next
;
137 insertElement(pH
, &new_ht
[h
], elem
);
142 /* This function (for internal use only) locates an element in an
143 ** hash table that matches the given key. If no element is found,
144 ** a pointer to a static null element with HashElem.data==0 is returned.
145 ** If pH is not NULL, then the hash for this key is written to *pH.
147 static HashElem
*findElementWithHash(
148 const Hash
*pH
, /* The pH to be searched */
149 const char *pKey
, /* The key we are searching for */
150 unsigned int *pHash
/* Write the hash value here */
152 HashElem
*elem
; /* Used to loop thru the element list */
153 unsigned int count
; /* Number of elements left to test */
154 unsigned int h
; /* The computed hash */
155 static HashElem nullElement
= { 0, 0, 0, 0 };
157 if( pH
->ht
){ /*OPTIMIZATION-IF-TRUE*/
159 h
= strHash(pKey
) % pH
->htsize
;
161 elem
= pEntry
->chain
;
162 count
= pEntry
->count
;
168 if( pHash
) *pHash
= h
;
171 if( sqlite3StrICmp(elem
->pKey
,pKey
)==0 ){
180 /* Remove a single entry from the hash table given a pointer to that
181 ** element and a hash on the element's key.
183 static void removeElementGivenHash(
184 Hash
*pH
, /* The pH containing "elem" */
185 HashElem
* elem
, /* The element to be removed from the pH */
186 unsigned int h
/* Hash value for the element */
190 elem
->prev
->next
= elem
->next
;
192 pH
->first
= elem
->next
;
195 elem
->next
->prev
= elem
->prev
;
199 if( pEntry
->chain
==elem
){
200 pEntry
->chain
= elem
->next
;
202 assert( pEntry
->count
>0 );
205 sqlite3_free( elem
);
208 assert( pH
->first
==0 );
209 assert( pH
->count
==0 );
210 sqlite3HashClear(pH
);
214 /* Attempt to locate an element of the hash table pH with a key
215 ** that matches pKey. Return the data for this element if it is
216 ** found, or NULL if there is no match.
218 void *sqlite3HashFind(const Hash
*pH
, const char *pKey
){
221 return findElementWithHash(pH
, pKey
, 0)->data
;
224 /* Insert an element into the hash table pH. The key is pKey
225 ** and the data is "data".
227 ** If no element exists with a matching key, then a new
228 ** element is created and NULL is returned.
230 ** If another element already exists with the same key, then the
231 ** new data replaces the old data and the old data is returned.
232 ** The key is not copied in this instance. If a malloc fails, then
233 ** the new data is returned and the hash table is unchanged.
235 ** If the "data" parameter to this function is NULL, then the
236 ** element corresponding to "key" is removed from the hash table.
238 void *sqlite3HashInsert(Hash
*pH
, const char *pKey
, void *data
){
239 unsigned int h
; /* the hash of the key modulo hash table size */
240 HashElem
*elem
; /* Used to loop thru the element list */
241 HashElem
*new_elem
; /* New element added to the pH */
245 elem
= findElementWithHash(pH
,pKey
,&h
);
247 void *old_data
= elem
->data
;
249 removeElementGivenHash(pH
,elem
,h
);
256 if( data
==0 ) return 0;
257 new_elem
= (HashElem
*)sqlite3Malloc( sizeof(HashElem
) );
258 if( new_elem
==0 ) return data
;
259 new_elem
->pKey
= pKey
;
260 new_elem
->data
= data
;
262 if( pH
->count
>=10 && pH
->count
> 2*pH
->htsize
){
263 if( rehash(pH
, pH
->count
*2) ){
264 assert( pH
->htsize
>0 );
265 h
= strHash(pKey
) % pH
->htsize
;
268 insertElement(pH
, pH
->ht
? &pH
->ht
[h
] : 0, new_elem
);