xref: /illumos-gate/usr/src/lib/libsqlite/src/hash.c (revision 1da57d551424de5a9d469760be7c4b4d4f10a755)
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 1.11 2004/01/08 02:17:33 drh 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 */
sqliteHashInit(Hash * new,int keyClass,int copyKey)32 void 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 */
sqliteHashClear(Hash * pH)48 void 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 */
intHash(const void * pKey,int nKey)71 static int intHash(const void *pKey, int nKey){
72   return nKey ^ (nKey<<8) ^ (nKey>>8);
73 }
intCompare(const void * pKey1,int n1,const void * pKey2,int n2)74 static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){
75   return n2 - n1;
76 }
77 
78 #if 0 /* NOT USED */
79 /*
80 ** Hash and comparison functions when the mode is SQLITE_HASH_POINTER
81 */
82 static int ptrHash(const void *pKey, int nKey){
83   uptr x = Addr(pKey);
84   return x ^ (x<<8) ^ (x>>8);
85 }
86 static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){
87   if( pKey1==pKey2 ) return 0;
88   if( pKey1<pKey2 ) return -1;
89   return 1;
90 }
91 #endif
92 
93 /*
94 ** Hash and comparison functions when the mode is SQLITE_HASH_STRING
95 */
strHash(const void * pKey,int nKey)96 static int strHash(const void *pKey, int nKey){
97   return sqliteHashNoCase((const char*)pKey, nKey);
98 }
strCompare(const void * pKey1,int n1,const void * pKey2,int n2)99 static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
100   if( n1!=n2 ) return n2-n1;
101   return sqliteStrNICmp((const char*)pKey1,(const char*)pKey2,n1);
102 }
103 
104 /*
105 ** Hash and comparison functions when the mode is SQLITE_HASH_BINARY
106 */
binHash(const void * pKey,int nKey)107 static int binHash(const void *pKey, int nKey){
108   int h = 0;
109   const char *z = (const char *)pKey;
110   while( nKey-- > 0 ){
111     h = (h<<3) ^ h ^ *(z++);
112   }
113   return h & 0x7fffffff;
114 }
binCompare(const void * pKey1,int n1,const void * pKey2,int n2)115 static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
116   if( n1!=n2 ) return n2-n1;
117   return memcmp(pKey1,pKey2,n1);
118 }
119 
120 /*
121 ** Return a pointer to the appropriate hash function given the key class.
122 **
123 ** The C syntax in this function definition may be unfamilar to some
124 ** programmers, so we provide the following additional explanation:
125 **
126 ** The name of the function is "hashFunction".  The function takes a
127 ** single parameter "keyClass".  The return value of hashFunction()
128 ** is a pointer to another function.  Specifically, the return value
129 ** of hashFunction() is a pointer to a function that takes two parameters
130 ** with types "const void*" and "int" and returns an "int".
131 */
hashFunction(int keyClass)132 static int (*hashFunction(int keyClass))(const void*,int){
133   switch( keyClass ){
134     case SQLITE_HASH_INT:     return &intHash;
135     /* case SQLITE_HASH_POINTER: return &ptrHash; // NOT USED */
136     case SQLITE_HASH_STRING:  return &strHash;
137     case SQLITE_HASH_BINARY:  return &binHash;;
138     default: break;
139   }
140   return 0;
141 }
142 
143 /*
144 ** Return a pointer to the appropriate hash function given the key class.
145 **
146 ** For help in interpreted the obscure C code in the function definition,
147 ** see the header comment on the previous function.
148 */
compareFunction(int keyClass)149 static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
150   switch( keyClass ){
151     case SQLITE_HASH_INT:     return &intCompare;
152     /* case SQLITE_HASH_POINTER: return &ptrCompare; // NOT USED */
153     case SQLITE_HASH_STRING:  return &strCompare;
154     case SQLITE_HASH_BINARY:  return &binCompare;
155     default: break;
156   }
157   return 0;
158 }
159 
160 
161 /* Resize the hash table so that it cantains "new_size" buckets.
162 ** "new_size" must be a power of 2.  The hash table might fail
163 ** to resize if sqliteMalloc() fails.
164 */
rehash(Hash * pH,int new_size)165 static void rehash(Hash *pH, int new_size){
166   struct _ht *new_ht;            /* The new hash table */
167   HashElem *elem, *next_elem;    /* For looping over existing elements */
168   HashElem *x;                   /* Element being copied to new hash table */
169   int (*xHash)(const void*,int); /* The hash function */
170 
171   assert( (new_size & (new_size-1))==0 );
172   new_ht = (struct _ht *)sqliteMalloc( new_size*sizeof(struct _ht) );
173   if( new_ht==0 ) return;
174   if( pH->ht ) sqliteFree(pH->ht);
175   pH->ht = new_ht;
176   pH->htsize = new_size;
177   xHash = hashFunction(pH->keyClass);
178   for(elem=pH->first, pH->first=0; elem; elem = next_elem){
179     int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
180     next_elem = elem->next;
181     x = new_ht[h].chain;
182     if( x ){
183       elem->next = x;
184       elem->prev = x->prev;
185       if( x->prev ) x->prev->next = elem;
186       else          pH->first = elem;
187       x->prev = elem;
188     }else{
189       elem->next = pH->first;
190       if( pH->first ) pH->first->prev = elem;
191       elem->prev = 0;
192       pH->first = elem;
193     }
194     new_ht[h].chain = elem;
195     new_ht[h].count++;
196   }
197 }
198 
199 /* This function (for internal use only) locates an element in an
200 ** hash table that matches the given key.  The hash for this key has
201 ** already been computed and is passed as the 4th parameter.
202 */
findElementGivenHash(const Hash * pH,const void * pKey,int nKey,int h)203 static HashElem *findElementGivenHash(
204   const Hash *pH,     /* The pH to be searched */
205   const void *pKey,   /* The key we are searching for */
206   int nKey,
207   int h               /* The hash for this key. */
208 ){
209   HashElem *elem;                /* Used to loop thru the element list */
210   int count;                     /* Number of elements left to test */
211   int (*xCompare)(const void*,int,const void*,int);  /* comparison function */
212 
213   if( pH->ht ){
214     elem = pH->ht[h].chain;
215     count = pH->ht[h].count;
216     xCompare = compareFunction(pH->keyClass);
217     while( count-- && elem ){
218       if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){
219         return elem;
220       }
221       elem = elem->next;
222     }
223   }
224   return 0;
225 }
226 
227 /* Remove a single entry from the hash table given a pointer to that
228 ** element and a hash on the element's key.
229 */
removeElementGivenHash(Hash * pH,HashElem * elem,int h)230 static void removeElementGivenHash(
231   Hash *pH,         /* The pH containing "elem" */
232   HashElem* elem,   /* The element to be removed from the pH */
233   int h             /* Hash value for the element */
234 ){
235   if( elem->prev ){
236     elem->prev->next = elem->next;
237   }else{
238     pH->first = elem->next;
239   }
240   if( elem->next ){
241     elem->next->prev = elem->prev;
242   }
243   if( pH->ht[h].chain==elem ){
244     pH->ht[h].chain = elem->next;
245   }
246   pH->ht[h].count--;
247   if( pH->ht[h].count<=0 ){
248     pH->ht[h].chain = 0;
249   }
250   if( pH->copyKey && elem->pKey ){
251     sqliteFree(elem->pKey);
252   }
253   sqliteFree( elem );
254   pH->count--;
255 }
256 
257 /* Attempt to locate an element of the hash table pH with a key
258 ** that matches pKey,nKey.  Return the data for this element if it is
259 ** found, or NULL if there is no match.
260 */
sqliteHashFind(const Hash * pH,const void * pKey,int nKey)261 void *sqliteHashFind(const Hash *pH, const void *pKey, int nKey){
262   int h;             /* A hash on key */
263   HashElem *elem;    /* The element that matches key */
264   int (*xHash)(const void*,int);  /* The hash function */
265 
266   if( pH==0 || pH->ht==0 ) return 0;
267   xHash = hashFunction(pH->keyClass);
268   assert( xHash!=0 );
269   h = (*xHash)(pKey,nKey);
270   assert( (pH->htsize & (pH->htsize-1))==0 );
271   elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
272   return elem ? elem->data : 0;
273 }
274 
275 /* Insert an element into the hash table pH.  The key is pKey,nKey
276 ** and the data is "data".
277 **
278 ** If no element exists with a matching key, then a new
279 ** element is created.  A copy of the key is made if the copyKey
280 ** flag is set.  NULL is returned.
281 **
282 ** If another element already exists with the same key, then the
283 ** new data replaces the old data and the old data is returned.
284 ** The key is not copied in this instance.  If a malloc fails, then
285 ** the new data is returned and the hash table is unchanged.
286 **
287 ** If the "data" parameter to this function is NULL, then the
288 ** element corresponding to "key" is removed from the hash table.
289 */
sqliteHashInsert(Hash * pH,const void * pKey,int nKey,void * data)290 void *sqliteHashInsert(Hash *pH, const void *pKey, int nKey, void *data){
291   int hraw;             /* Raw hash value of the key */
292   int h;                /* the hash of the key modulo hash table size */
293   HashElem *elem;       /* Used to loop thru the element list */
294   HashElem *new_elem;   /* New element added to the pH */
295   int (*xHash)(const void*,int);  /* The hash function */
296 
297   assert( pH!=0 );
298   xHash = hashFunction(pH->keyClass);
299   assert( xHash!=0 );
300   hraw = (*xHash)(pKey, nKey);
301   assert( (pH->htsize & (pH->htsize-1))==0 );
302   h = hraw & (pH->htsize-1);
303   elem = findElementGivenHash(pH,pKey,nKey,h);
304   if( elem ){
305     void *old_data = elem->data;
306     if( data==0 ){
307       removeElementGivenHash(pH,elem,h);
308     }else{
309       elem->data = data;
310     }
311     return old_data;
312   }
313   if( data==0 ) return 0;
314   new_elem = (HashElem*)sqliteMalloc( sizeof(HashElem) );
315   if( new_elem==0 ) return data;
316   if( pH->copyKey && pKey!=0 ){
317     new_elem->pKey = sqliteMallocRaw( nKey );
318     if( new_elem->pKey==0 ){
319       sqliteFree(new_elem);
320       return data;
321     }
322     memcpy((void*)new_elem->pKey, pKey, nKey);
323   }else{
324     new_elem->pKey = (void*)pKey;
325   }
326   new_elem->nKey = nKey;
327   pH->count++;
328   if( pH->htsize==0 ) rehash(pH,8);
329   if( pH->htsize==0 ){
330     pH->count = 0;
331     sqliteFree(new_elem);
332     return data;
333   }
334   if( pH->count > pH->htsize ){
335     rehash(pH,pH->htsize*2);
336   }
337   assert( (pH->htsize & (pH->htsize-1))==0 );
338   h = hraw & (pH->htsize-1);
339   elem = pH->ht[h].chain;
340   if( elem ){
341     new_elem->next = elem;
342     new_elem->prev = elem->prev;
343     if( elem->prev ){ elem->prev->next = new_elem; }
344     else            { pH->first = new_elem; }
345     elem->prev = new_elem;
346   }else{
347     new_elem->next = pH->first;
348     new_elem->prev = 0;
349     if( pH->first ){ pH->first->prev = new_elem; }
350     pH->first = new_elem;
351   }
352   pH->ht[h].count++;
353   pH->ht[h].chain = new_elem;
354   new_elem->data = data;
355   return 0;
356 }
357