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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 1.24 2007/09/04 14:31:47 danielk1977 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** "pNew" 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 sqlite3HashInit(Hash *pNew, int keyClass, int copyKey){
33 assert( pNew!=0 );
34 assert( keyClass>=SQLITE_HASH_STRING && keyClass<=SQLITE_HASH_BINARY );
35 pNew->keyClass = keyClass;
36#if 0
37 if( keyClass==SQLITE_HASH_POINTER || keyClass==SQLITE_HASH_INT ) copyKey = 0;
38#endif
39 pNew->copyKey = copyKey;
40 pNew->first = 0;
41 pNew->count = 0;
42 pNew->htsize = 0;
43 pNew->ht = 0;
44}
45
46/* Remove all entries from a hash table. Reclaim all memory.
47** Call this routine to delete a hash table or to reset a hash table
48** to the empty state.
49*/
50void sqlite3HashClear(Hash *pH){
51 HashElem *elem; /* For looping over all elements of the table */
52
53 assert( pH!=0 );
54 elem = pH->first;
55 pH->first = 0;
56 if( pH->ht ) sqlite3_free(pH->ht);
57 pH->ht = 0;
58 pH->htsize = 0;
59 while( elem ){
60 HashElem *next_elem = elem->next;
61 if( pH->copyKey && elem->pKey ){
62 sqlite3_free(elem->pKey);
63 }
64 sqlite3_free(elem);
65 elem = next_elem;
66 }
67 pH->count = 0;
68}
69
70#if 0 /* NOT USED */
71/*
72** Hash and comparison functions when the mode is SQLITE_HASH_INT
73*/
74static int intHash(const void *pKey, int nKey){
75 return nKey ^ (nKey<<8) ^ (nKey>>8);
76}
77static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){
78 return n2 - n1;
79}
80#endif
81
82#if 0 /* NOT USED */
83/*
84** Hash and comparison functions when the mode is SQLITE_HASH_POINTER
85*/
86static int ptrHash(const void *pKey, int nKey){
87 uptr x = Addr(pKey);
88 return x ^ (x<<8) ^ (x>>8);
89}
90static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){
91 if( pKey1==pKey2 ) return 0;
92 if( pKey1<pKey2 ) return -1;
93 return 1;
94}
95#endif
96
97/*
98** Hash and comparison functions when the mode is SQLITE_HASH_STRING
99*/
100static int strHash(const void *pKey, int nKey){
101 const char *z = (const char *)pKey;
102 int h = 0;
103 if( nKey<=0 ) nKey = strlen(z);
104 while( nKey > 0 ){
105 h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++];
106 nKey--;
107 }
108 return h & 0x7fffffff;
109}
110static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
111 if( n1!=n2 ) return 1;
112 return sqlite3StrNICmp((const char*)pKey1,(const char*)pKey2,n1);
113}
114
115/*
116** Hash and comparison functions when the mode is SQLITE_HASH_BINARY
117*/
118static int binHash(const void *pKey, int nKey){
119 int h = 0;
120 const char *z = (const char *)pKey;
121 while( nKey-- > 0 ){
122 h = (h<<3) ^ h ^ *(z++);
123 }
124 return h & 0x7fffffff;
125}
126static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
127 if( n1!=n2 ) return 1;
128 return memcmp(pKey1,pKey2,n1);
129}
130
131/*
132** Return a pointer to the appropriate hash function given the key class.
133**
134** The C syntax in this function definition may be unfamilar to some
135** programmers, so we provide the following additional explanation:
136**
137** The name of the function is "hashFunction". The function takes a
138** single parameter "keyClass". The return value of hashFunction()
139** is a pointer to another function. Specifically, the return value
140** of hashFunction() is a pointer to a function that takes two parameters
141** with types "const void*" and "int" and returns an "int".
142*/
143static int (*hashFunction(int keyClass))(const void*,int){
144#if 0 /* HASH_INT and HASH_POINTER are never used */
145 switch( keyClass ){
146 case SQLITE_HASH_INT: return &intHash;
147 case SQLITE_HASH_POINTER: return &ptrHash;
148 case SQLITE_HASH_STRING: return &strHash;
149 case SQLITE_HASH_BINARY: return &binHash;;
150 default: break;
151 }
152 return 0;
153#else
154 if( keyClass==SQLITE_HASH_STRING ){
155 return &strHash;
156 }else{
157 assert( keyClass==SQLITE_HASH_BINARY );
158 return &binHash;
159 }
160#endif
161}
162
163/*
164** Return a pointer to the appropriate hash function given the key class.
165**
166** For help in interpreted the obscure C code in the function definition,
167** see the header comment on the previous function.
168*/
169static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
170#if 0 /* HASH_INT and HASH_POINTER are never used */
171 switch( keyClass ){
172 case SQLITE_HASH_INT: return &intCompare;
173 case SQLITE_HASH_POINTER: return &ptrCompare;
174 case SQLITE_HASH_STRING: return &strCompare;
175 case SQLITE_HASH_BINARY: return &binCompare;
176 default: break;
177 }
178 return 0;
179#else
180 if( keyClass==SQLITE_HASH_STRING ){
181 return &strCompare;
182 }else{
183 assert( keyClass==SQLITE_HASH_BINARY );
184 return &binCompare;
185 }
186#endif
187}
188
189/* Link an element into the hash table
190*/
191static void insertElement(
192 Hash *pH, /* The complete hash table */
193 struct _ht *pEntry, /* The entry into which pNew is inserted */
194 HashElem *pNew /* The element to be inserted */
195){
196 HashElem *pHead; /* First element already in pEntry */
197 pHead = pEntry->chain;
198 if( pHead ){
199 pNew->next = pHead;
200 pNew->prev = pHead->prev;
201 if( pHead->prev ){ pHead->prev->next = pNew; }
202 else { pH->first = pNew; }
203 pHead->prev = pNew;
204 }else{
205 pNew->next = pH->first;
206 if( pH->first ){ pH->first->prev = pNew; }
207 pNew->prev = 0;
208 pH->first = pNew;
209 }
210 pEntry->count++;
211 pEntry->chain = pNew;
212}
213
214
215/* Resize the hash table so that it cantains "new_size" buckets.
216** "new_size" must be a power of 2. The hash table might fail
217** to resize if sqlite3_malloc() fails.
218*/
219static void rehash(Hash *pH, int new_size){
220 struct _ht *new_ht; /* The new hash table */
221 HashElem *elem, *next_elem; /* For looping over existing elements */
222 int (*xHash)(const void*,int); /* The hash function */
223
224 assert( (new_size & (new_size-1))==0 );
225
226 /* There is a call to sqlite3_malloc() inside rehash(). If there is
227 ** already an allocation at pH->ht, then if this malloc() fails it
228 ** is benign (since failing to resize a hash table is a performance
229 ** hit only, not a fatal error).
230 */
231 sqlite3MallocBenignFailure(pH->htsize>0);
232
233 new_ht = (struct _ht *)sqlite3MallocZero( new_size*sizeof(struct _ht) );
234 if( new_ht==0 ) return;
235 if( pH->ht ) sqlite3_free(pH->ht);
236 pH->ht = new_ht;
237 pH->htsize = new_size;
238 xHash = hashFunction(pH->keyClass);
239 for(elem=pH->first, pH->first=0; elem; elem = next_elem){
240 int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
241 next_elem = elem->next;
242 insertElement(pH, &new_ht[h], elem);
243 }
244}
245
246/* This function (for internal use only) locates an element in an
247** hash table that matches the given key. The hash for this key has
248** already been computed and is passed as the 4th parameter.
249*/
250static HashElem *findElementGivenHash(
251 const Hash *pH, /* The pH to be searched */
252 const void *pKey, /* The key we are searching for */
253 int nKey,
254 int h /* The hash for this key. */
255){
256 HashElem *elem; /* Used to loop thru the element list */
257 int count; /* Number of elements left to test */
258 int (*xCompare)(const void*,int,const void*,int); /* comparison function */
259
260 if( pH->ht ){
261 struct _ht *pEntry = &pH->ht[h];
262 elem = pEntry->chain;
263 count = pEntry->count;
264 xCompare = compareFunction(pH->keyClass);
265 while( count-- && elem ){
266 if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){
267 return elem;
268 }
269 elem = elem->next;
270 }
271 }
272 return 0;
273}
274
275/* Remove a single entry from the hash table given a pointer to that
276** element and a hash on the element's key.
277*/
278static void removeElementGivenHash(
279 Hash *pH, /* The pH containing "elem" */
280 HashElem* elem, /* The element to be removed from the pH */
281 int h /* Hash value for the element */
282){
283 struct _ht *pEntry;
284 if( elem->prev ){
285 elem->prev->next = elem->next;
286 }else{
287 pH->first = elem->next;
288 }
289 if( elem->next ){
290 elem->next->prev = elem->prev;
291 }
292 pEntry = &pH->ht[h];
293 if( pEntry->chain==elem ){
294 pEntry->chain = elem->next;
295 }
296 pEntry->count--;
297 if( pEntry->count<=0 ){
298 pEntry->chain = 0;
299 }
300 if( pH->copyKey ){
301 sqlite3_free(elem->pKey);
302 }
303 sqlite3_free( elem );
304 pH->count--;
305 if( pH->count<=0 ){
306 assert( pH->first==0 );
307 assert( pH->count==0 );
308 sqlite3HashClear(pH);
309 }
310}
311
312/* Attempt to locate an element of the hash table pH with a key
313** that matches pKey,nKey. Return a pointer to the corresponding
314** HashElem structure for this element if it is found, or NULL
315** otherwise.
316*/
317HashElem *sqlite3HashFindElem(const Hash *pH, const void *pKey, int nKey){
318 int h; /* A hash on key */
319 HashElem *elem; /* The element that matches key */
320 int (*xHash)(const void*,int); /* The hash function */
321
322 if( pH==0 || pH->ht==0 ) return 0;
323 xHash = hashFunction(pH->keyClass);
324 assert( xHash!=0 );
325 h = (*xHash)(pKey,nKey);
326 assert( (pH->htsize & (pH->htsize-1))==0 );
327 elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
328 return elem;
329}
330
331/* Attempt to locate an element of the hash table pH with a key
332** that matches pKey,nKey. Return the data for this element if it is
333** found, or NULL if there is no match.
334*/
335void *sqlite3HashFind(const Hash *pH, const void *pKey, int nKey){
336 HashElem *elem; /* The element that matches key */
337 elem = sqlite3HashFindElem(pH, pKey, nKey);
338 return elem ? elem->data : 0;
339}
340
341/* Insert an element into the hash table pH. The key is pKey,nKey
342** and the data is "data".
343**
344** If no element exists with a matching key, then a new
345** element is created. A copy of the key is made if the copyKey
346** flag is set. NULL is returned.
347**
348** If another element already exists with the same key, then the
349** new data replaces the old data and the old data is returned.
350** The key is not copied in this instance. If a malloc fails, then
351** the new data is returned and the hash table is unchanged.
352**
353** If the "data" parameter to this function is NULL, then the
354** element corresponding to "key" is removed from the hash table.
355*/
356void *sqlite3HashInsert(Hash *pH, const void *pKey, int nKey, void *data){
357 int hraw; /* Raw hash value of the key */
358 int h; /* the hash of the key modulo hash table size */
359 HashElem *elem; /* Used to loop thru the element list */
360 HashElem *new_elem; /* New element added to the pH */
361 int (*xHash)(const void*,int); /* The hash function */
362
363 assert( pH!=0 );
364 xHash = hashFunction(pH->keyClass);
365 assert( xHash!=0 );
366 hraw = (*xHash)(pKey, nKey);
367 assert( (pH->htsize & (pH->htsize-1))==0 );
368 h = hraw & (pH->htsize-1);
369 elem = findElementGivenHash(pH,pKey,nKey,h);
370 if( elem ){
371 void *old_data = elem->data;
372 if( data==0 ){
373 removeElementGivenHash(pH,elem,h);
374 }else{
375 elem->data = data;
376 if( !pH->copyKey ){
377 elem->pKey = (void *)pKey;
378 }
379 assert(nKey==elem->nKey);
380 }
381 return old_data;
382 }
383 if( data==0 ) return 0;
384 new_elem = (HashElem*)sqlite3_malloc( sizeof(HashElem) );
385 if( new_elem==0 ) return data;
386 if( pH->copyKey && pKey!=0 ){
387 new_elem->pKey = sqlite3_malloc( nKey );
388 if( new_elem->pKey==0 ){
389 sqlite3_free(new_elem);
390 return data;
391 }
392 memcpy((void*)new_elem->pKey, pKey, nKey);
393 }else{
394 new_elem->pKey = (void*)pKey;
395 }
396 new_elem->nKey = nKey;
397 pH->count++;
398 if( pH->htsize==0 ){
399 rehash(pH,8);
400 if( pH->htsize==0 ){
401 pH->count = 0;
402 if( pH->copyKey ){
403 sqlite3_free(new_elem->pKey);
404 }
405 sqlite3_free(new_elem);
406 return data;
407 }
408 }
409 if( pH->count > pH->htsize ){
410 rehash(pH,pH->htsize*2);
411 }
412 assert( pH->htsize>0 );
413 assert( (pH->htsize & (pH->htsize-1))==0 );
414 h = hraw & (pH->htsize-1);
415 insertElement(pH, &pH->ht[h], new_elem);
416 new_elem->data = data;
417 return 0;
418}