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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** $Id: hash.c,v 1.1 2003/08/05 23:03:07 graydon Exp $
16*/
17#include "sqliteInt.h"
18#include <assert.h>
19
20/* Turn bulk memory into a hash table object by initializing the
21** fields of the Hash structure.
22**
23** "new" is a pointer to the hash table that is to be initialized.
24** keyClass is one of the constants SQLITE_HASH_INT, SQLITE_HASH_POINTER,
25** SQLITE_HASH_BINARY, or SQLITE_HASH_STRING. The value of keyClass
26** determines what kind of key the hash table will use. "copyKey" is
27** true if the hash table should make its own private copy of keys and
28** false if it should just use the supplied pointer. CopyKey only makes
29** sense for SQLITE_HASH_STRING and SQLITE_HASH_BINARY and is ignored
30** for other key classes.
31*/
32void sqliteHashInit(Hash *new, int keyClass, int copyKey){
33 assert( new!=0 );
34 assert( keyClass>=SQLITE_HASH_INT && keyClass<=SQLITE_HASH_BINARY );
35 new->keyClass = keyClass;
36 new->copyKey = copyKey &&
37 (keyClass==SQLITE_HASH_STRING || keyClass==SQLITE_HASH_BINARY);
38 new->first = 0;
39 new->count = 0;
40 new->htsize = 0;
41 new->ht = 0;
42}
43
44/* Remove all entries from a hash table. Reclaim all memory.
45** Call this routine to delete a hash table or to reset a hash table
46** to the empty state.
47*/
48void sqliteHashClear(Hash *pH){
49 HashElem *elem; /* For looping over all elements of the table */
50
51 assert( pH!=0 );
52 elem = pH->first;
53 pH->first = 0;
54 if( pH->ht ) sqliteFree(pH->ht);
55 pH->ht = 0;
56 pH->htsize = 0;
57 while( elem ){
58 HashElem *next_elem = elem->next;
59 if( pH->copyKey && elem->pKey ){
60 sqliteFree(elem->pKey);
61 }
62 sqliteFree(elem);
63 elem = next_elem;
64 }
65 pH->count = 0;
66}
67
68/*
69** Hash and comparison functions when the mode is SQLITE_HASH_INT
70*/
71static int intHash(const void *pKey, int nKey){
72 return nKey ^ (nKey<<8) ^ (nKey>>8);
73}
74static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){
75 return n2 - n1;
76}
77
78/*
79** Hash and comparison functions when the mode is SQLITE_HASH_POINTER
80*/
81static int ptrHash(const void *pKey, int nKey){
82 uptr x = Addr(pKey);
83 return x ^ (x<<8) ^ (x>>8);
84}
85static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){
86 if( pKey1==pKey2 ) return 0;
87 if( pKey1<pKey2 ) return -1;
88 return 1;
89}
90
91/*
92** Hash and comparison functions when the mode is SQLITE_HASH_STRING
93*/
94static int strHash(const void *pKey, int nKey){
95 return sqliteHashNoCase((const char*)pKey, nKey);
96}
97static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
98 if( n1!=n2 ) return n2-n1;
99 return sqliteStrNICmp((const char*)pKey1,(const char*)pKey2,n1);
100}
101
102/*
103** Hash and comparison functions when the mode is SQLITE_HASH_BINARY
104*/
105static int binHash(const void *pKey, int nKey){
106 int h = 0;
107 const char *z = (const char *)pKey;
108 while( nKey-- > 0 ){
109 h = (h<<3) ^ h ^ *(z++);
110 }
111 return h & 0x7fffffff;
112}
113static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
114 if( n1!=n2 ) return n2-n1;
115 return memcmp(pKey1,pKey2,n1);
116}
117
118/*
119** Return a pointer to the appropriate hash function given the key class.
120**
121** The C syntax in this function definition may be unfamilar to some
122** programmers, so we provide the following additional explanation:
123**
124** The name of the function is "hashFunction". The function takes a
125** single parameter "keyClass". The return value of hashFunction()
126** is a pointer to another function. Specifically, the return value
127** of hashFunction() is a pointer to a function that takes two parameters
128** with types "const void*" and "int" and returns an "int".
129*/
130static int (*hashFunction(int keyClass))(const void*,int){
131 switch( keyClass ){
132 case SQLITE_HASH_INT: return &intHash;
133 case SQLITE_HASH_POINTER: return &ptrHash;
134 case SQLITE_HASH_STRING: return &strHash;
135 case SQLITE_HASH_BINARY: return &binHash;;
136 default: break;
137 }
138 return 0;
139}
140
141/*
142** Return a pointer to the appropriate hash function given the key class.
143**
144** For help in interpreted the obscure C code in the function definition,
145** see the header comment on the previous function.
146*/
147static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
148 switch( keyClass ){
149 case SQLITE_HASH_INT: return &intCompare;
150 case SQLITE_HASH_POINTER: return &ptrCompare;
151 case SQLITE_HASH_STRING: return &strCompare;
152 case SQLITE_HASH_BINARY: return &binCompare;
153 default: break;
154 }
155 return 0;
156}
157
158
159/* Resize the hash table so that it cantains "new_size" buckets.
160** "new_size" must be a power of 2. The hash table might fail
161** to resize if sqliteMalloc() fails.
162*/
163static void rehash(Hash *pH, int new_size){
164 struct _ht *new_ht; /* The new hash table */
165 HashElem *elem, *next_elem; /* For looping over existing elements */
166 HashElem *x; /* Element being copied to new hash table */
167 int (*xHash)(const void*,int); /* The hash function */
168
169 assert( (new_size & (new_size-1))==0 );
170 new_ht = (struct _ht *)sqliteMalloc( new_size*sizeof(struct _ht) );
171 if( new_ht==0 ) return;
172 if( pH->ht ) sqliteFree(pH->ht);
173 pH->ht = new_ht;
174 pH->htsize = new_size;
175 xHash = hashFunction(pH->keyClass);
176 for(elem=pH->first, pH->first=0; elem; elem = next_elem){
177 int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
178 next_elem = elem->next;
179 x = new_ht[h].chain;
180 if( x ){
181 elem->next = x;
182 elem->prev = x->prev;
183 if( x->prev ) x->prev->next = elem;
184 else pH->first = elem;
185 x->prev = elem;
186 }else{
187 elem->next = pH->first;
188 if( pH->first ) pH->first->prev = elem;
189 elem->prev = 0;
190 pH->first = elem;
191 }
192 new_ht[h].chain = elem;
193 new_ht[h].count++;
194 }
195}
196
197/* This function (for internal use only) locates an element in an
198** hash table that matches the given key. The hash for this key has
199** already been computed and is passed as the 4th parameter.
200*/
201static HashElem *findElementGivenHash(
202 const Hash *pH, /* The pH to be searched */
203 const void *pKey, /* The key we are searching for */
204 int nKey,
205 int h /* The hash for this key. */
206){
207 HashElem *elem; /* Used to loop thru the element list */
208 int count; /* Number of elements left to test */
209 int (*xCompare)(const void*,int,const void*,int); /* comparison function */
210
211 if( pH->ht ){
212 elem = pH->ht[h].chain;
213 count = pH->ht[h].count;
214 xCompare = compareFunction(pH->keyClass);
215 while( count-- && elem ){
216 if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){
217 return elem;
218 }
219 elem = elem->next;
220 }
221 }
222 return 0;
223}
224
225/* Remove a single entry from the hash table given a pointer to that
226** element and a hash on the element's key.
227*/
228static void removeElementGivenHash(
229 Hash *pH, /* The pH containing "elem" */
230 HashElem* elem, /* The element to be removed from the pH */
231 int h /* Hash value for the element */
232){
233 if( elem->prev ){
234 elem->prev->next = elem->next;
235 }else{
236 pH->first = elem->next;
237 }
238 if( elem->next ){
239 elem->next->prev = elem->prev;
240 }
241 if( pH->ht[h].chain==elem ){
242 pH->ht[h].chain = elem->next;
243 }
244 pH->ht[h].count--;
245 if( pH->ht[h].count<=0 ){
246 pH->ht[h].chain = 0;
247 }
248 if( pH->copyKey && elem->pKey ){
249 sqliteFree(elem->pKey);
250 }
251 sqliteFree( elem );
252 pH->count--;
253}
254
255/* Attempt to locate an element of the hash table pH with a key
256** that matches pKey,nKey. Return the data for this element if it is
257** found, or NULL if there is no match.
258*/
259void *sqliteHashFind(const Hash *pH, const void *pKey, int nKey){
260 int h; /* A hash on key */
261 HashElem *elem; /* The element that matches key */
262 int (*xHash)(const void*,int); /* The hash function */
263
264 if( pH==0 || pH->ht==0 ) return 0;
265 xHash = hashFunction(pH->keyClass);
266 assert( xHash!=0 );
267 h = (*xHash)(pKey,nKey);
268 assert( (pH->htsize & (pH->htsize-1))==0 );
269 elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
270 return elem ? elem->data : 0;
271}
272
273/* Insert an element into the hash table pH. The key is pKey,nKey
274** and the data is "data".
275**
276** If no element exists with a matching key, then a new
277** element is created. A copy of the key is made if the copyKey
278** flag is set. NULL is returned.
279**
280** If another element already exists with the same key, then the
281** new data replaces the old data and the old data is returned.
282** The key is not copied in this instance. If a malloc fails, then
283** the new data is returned and the hash table is unchanged.
284**
285** If the "data" parameter to this function is NULL, then the
286** element corresponding to "key" is removed from the hash table.
287*/
288void *sqliteHashInsert(Hash *pH, const void *pKey, int nKey, void *data){
289 int hraw; /* Raw hash value of the key */
290 int h; /* the hash of the key modulo hash table size */
291 HashElem *elem; /* Used to loop thru the element list */
292 HashElem *new_elem; /* New element added to the pH */
293 int (*xHash)(const void*,int); /* The hash function */
294
295 assert( pH!=0 );
296 xHash = hashFunction(pH->keyClass);
297 assert( xHash!=0 );
298 hraw = (*xHash)(pKey, nKey);
299 assert( (pH->htsize & (pH->htsize-1))==0 );
300 h = hraw & (pH->htsize-1);
301 elem = findElementGivenHash(pH,pKey,nKey,h);
302 if( elem ){
303 void *old_data = elem->data;
304 if( data==0 ){
305 removeElementGivenHash(pH,elem,h);
306 }else{
307 elem->data = data;
308 }
309 return old_data;
310 }
311 if( data==0 ) return 0;
312 new_elem = (HashElem*)sqliteMalloc( sizeof(HashElem) );
313 if( new_elem==0 ) return data;
314 if( pH->copyKey && pKey!=0 ){
315 new_elem->pKey = sqliteMallocRaw( nKey );
316 if( new_elem->pKey==0 ){
317 sqliteFree(new_elem);
318 return data;
319 }
320 memcpy((void*)new_elem->pKey, pKey, nKey);
321 }else{
322 new_elem->pKey = (void*)pKey;
323 }
324 new_elem->nKey = nKey;
325 pH->count++;
326 if( pH->htsize==0 ) rehash(pH,8);
327 if( pH->htsize==0 ){
328 pH->count = 0;
329 sqliteFree(new_elem);
330 return data;
331 }
332 if( pH->count > pH->htsize ){
333 rehash(pH,pH->htsize*2);
334 }
335 assert( (pH->htsize & (pH->htsize-1))==0 );
336 h = hraw & (pH->htsize-1);
337 elem = pH->ht[h].chain;
338 if( elem ){
339 new_elem->next = elem;
340 new_elem->prev = elem->prev;
341 if( elem->prev ){ elem->prev->next = new_elem; }
342 else { pH->first = new_elem; }
343 elem->prev = new_elem;
344 }else{
345 new_elem->next = pH->first;
346 new_elem->prev = 0;
347 if( pH->first ){ pH->first->prev = new_elem; }
348 pH->first = new_elem;
349 }
350 pH->ht[h].count++;
351 pH->ht[h].chain = new_elem;
352 new_elem->data = data;
353 return 0;
354}

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