1/*
2** 2001 September 22
3**
4** The author disclaims copyright to this source code. In place of
5** a legal notice, here is a blessing:
6**
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.
10**
11*************************************************************************
12** This is the implementation of generic hash-tables
13** used in SQLite.
14*/
15#include "sqliteInt.h"
16#include <assert.h>
17
18/* Turn bulk memory into a hash table object by initializing the
19** fields of the Hash structure.
20**
21** "pNew" is a pointer to the hash table that is to be initialized.
22*/
23void sqlite3HashInit(Hash *pNew){
24 assert( pNew!=0 );
25 pNew->first = 0;
26 pNew->count = 0;
27 pNew->htsize = 0;
28 pNew->ht = 0;
29}
30
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.
34*/
35void sqlite3HashClear(Hash *pH){
36 HashElem *elem; /* For looping over all elements of the table */
37
38 assert( pH!=0 );
39 elem = pH->first;
40 pH->first = 0;
41 sqlite3_free(pH->ht);
42 pH->ht = 0;
43 pH->htsize = 0;
44 while( elem ){
45 HashElem *next_elem = elem->next;
46 sqlite3_free(elem);
47 elem = next_elem;
48 }
49 pH->count = 0;
50}
51
52/*
53** The hashing function.
54*/
55static unsigned int strHash(const char *z){
56 unsigned int h = 0;
57 unsigned char c;
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];
63 h *= 0x9e3779b1;
64 }
65 return h;
66}
67
68
69/* Link pNew element into the hash table pH. If pEntry!=0 then also
70** insert pNew into the pEntry hash bucket.
71*/
72static 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 */
76){
77 HashElem *pHead; /* First element already in pEntry */
78 if( pEntry ){
79 pHead = pEntry->count ? pEntry->chain : 0;
80 pEntry->count++;
81 pEntry->chain = pNew;
82 }else{
83 pHead = 0;
84 }
85 if( pHead ){
86 pNew->next = pHead;
87 pNew->prev = pHead->prev;
88 if( pHead->prev ){ pHead->prev->next = pNew; }
89 else { pH->first = pNew; }
90 pHead->prev = pNew;
91 }else{
92 pNew->next = pH->first;
93 if( pH->first ){ pH->first->prev = pNew; }
94 pNew->prev = 0;
95 pH->first = pNew;
96 }
97}
98
99
100/* Resize the hash table so that it cantains "new_size" buckets.
101**
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.
105*/
106static 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 */
109
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);
113 }
114 if( new_size==pH->htsize ) return 0;
115#endif
116
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).
124 */
125 sqlite3BeginBenignMalloc();
126 new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );
127 sqlite3EndBenignMalloc();
128
129 if( new_ht==0 ) return 0;
130 sqlite3_free(pH->ht);
131 pH->ht = new_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);
138 }
139 return 1;
140}
141
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.
146*/
147static 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 */
151){
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 };
156
157 if( pH->ht ){ /*OPTIMIZATION-IF-TRUE*/
158 struct _ht *pEntry;
159 h = strHash(pKey) % pH->htsize;
160 pEntry = &pH->ht[h];
161 elem = pEntry->chain;
162 count = pEntry->count;
163 }else{
164 h = 0;
165 elem = pH->first;
166 count = pH->count;
167 }
168 if( pHash ) *pHash = h;
169 while( count-- ){
170 assert( elem!=0 );
171 if( sqlite3StrICmp(elem->pKey,pKey)==0 ){
172 return elem;
173 }
174 elem = elem->next;
175 }
176 return &nullElement;
177}
178
179/* Remove a single entry from the hash table given a pointer to that
180** element and a hash on the element's key.
181*/
182static void removeElementGivenHash(
183 Hash *pH, /* The pH containing "elem" */
184 HashElem* elem, /* The element to be removed from the pH */
185 unsigned int h /* Hash value for the element */
186){
187 struct _ht *pEntry;
188 if( elem->prev ){
189 elem->prev->next = elem->next;
190 }else{
191 pH->first = elem->next;
192 }
193 if( elem->next ){
194 elem->next->prev = elem->prev;
195 }
196 if( pH->ht ){
197 pEntry = &pH->ht[h];
198 if( pEntry->chain==elem ){
199 pEntry->chain = elem->next;
200 }
201 assert( pEntry->count>0 );
202 pEntry->count--;
203 }
204 sqlite3_free( elem );
205 pH->count--;
206 if( pH->count==0 ){
207 assert( pH->first==0 );
208 assert( pH->count==0 );
209 sqlite3HashClear(pH);
210 }
211}
212
213/* Attempt to locate an element of the hash table pH with a key
214** that matches pKey. Return the data for this element if it is
215** found, or NULL if there is no match.
216*/
217void *sqlite3HashFind(const Hash *pH, const char *pKey){
218 assert( pH!=0 );
219 assert( pKey!=0 );
220 return findElementWithHash(pH, pKey, 0)->data;
221}
222
223/* Insert an element into the hash table pH. The key is pKey
224** and the data is "data".
225**
226** If no element exists with a matching key, then a new
227** element is created and NULL is returned.
228**
229** If another element already exists with the same key, then the
230** new data replaces the old data and the old data is returned.
231** The key is not copied in this instance. If a malloc fails, then
232** the new data is returned and the hash table is unchanged.
233**
234** If the "data" parameter to this function is NULL, then the
235** element corresponding to "key" is removed from the hash table.
236*/
237void *sqlite3HashInsert(Hash *pH, const char *pKey, void *data){
238 unsigned int h; /* the hash of the key modulo hash table size */
239 HashElem *elem; /* Used to loop thru the element list */
240 HashElem *new_elem; /* New element added to the pH */
241
242 assert( pH!=0 );
243 assert( pKey!=0 );
244 elem = findElementWithHash(pH,pKey,&h);
245 if( elem->data ){
246 void *old_data = elem->data;
247 if( data==0 ){
248 removeElementGivenHash(pH,elem,h);
249 }else{
250 elem->data = data;
251 elem->pKey = pKey;
252 }
253 return old_data;
254 }
255 if( data==0 ) return 0;
256 new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );
257 if( new_elem==0 ) return data;
258 new_elem->pKey = pKey;
259 new_elem->data = data;
260 pH->count++;
261 if( pH->count>=10 && pH->count > 2*pH->htsize ){
262 if( rehash(pH, pH->count*2) ){
263 assert( pH->htsize>0 );
264 h = strHash(pKey) % pH->htsize;
265 }
266 }
267 insertElement(pH, pH->ht ? &pH->ht[h] : 0, new_elem);
268 return 0;
269}
270