AryaWu/sqlite
0
1/*2** 2001 September 223**4** The author disclaims copyright to this source code. In place of5** 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-tables13** used in SQLite.14*/15#include "sqliteInt.h"16#include <assert.h>17 18/* Turn bulk memory into a hash table object by initializing the19** 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 table33** 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 while( z[0] ){ /*OPTIMIZATION-IF-TRUE*/58 /* Knuth multiplicative hashing. (Sorting & Searching, p. 510).59 ** 0x9e3779b1 is 2654435761 which is the closest prime number to60 ** (2**32)*golden_ratio, where golden_ratio = (sqrt(5) - 1)/2.61 **62 ** Only bits 0xdf for ASCII and bits 0xbf for EBCDIC each octet are63 ** hashed since the omitted bits determine the upper/lower case difference.64 */65#ifdef SQLITE_EBCDIC66 h += 0xbf & (unsigned char)*(z++);67#else68 h += 0xdf & (unsigned char)*(z++);69#endif70 h *= 0x9e3779b1;71 }72 return h;73}74 75 76/* Link pNew element into the hash table pH. If pEntry!=0 then also77** insert pNew into the pEntry hash bucket.78*/79static void insertElement(80 Hash *pH, /* The complete hash table */81 struct _ht *pEntry, /* The entry into which pNew is inserted */82 HashElem *pNew /* The element to be inserted */83){84 HashElem *pHead; /* First element already in pEntry */85 if( pEntry ){86 pHead = pEntry->count ? pEntry->chain : 0;87 pEntry->count++;88 pEntry->chain = pNew;89 }else{90 pHead = 0;91 }92 if( pHead ){93 pNew->next = pHead;94 pNew->prev = pHead->prev;95 if( pHead->prev ){ pHead->prev->next = pNew; }96 else { pH->first = pNew; }97 pHead->prev = pNew;98 }else{99 pNew->next = pH->first;100 if( pH->first ){ pH->first->prev = pNew; }101 pNew->prev = 0;102 pH->first = pNew;103 }104}105 106 107/* Resize the hash table so that it contains "new_size" buckets.108**109** The hash table might fail to resize if sqlite3_malloc() fails or110** if the new size is the same as the prior size.111** Return TRUE if the resize occurs and false if not.112*/113static int rehash(Hash *pH, unsigned int new_size){114 struct _ht *new_ht; /* The new hash table */115 HashElem *elem, *next_elem; /* For looping over existing elements */116 117#if SQLITE_MALLOC_SOFT_LIMIT>0118 if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){119 new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht);120 }121 if( new_size==pH->htsize ) return 0;122#endif123 124 /* The inability to allocates space for a larger hash table is125 ** a performance hit but it is not a fatal error. So mark the126 ** allocation as a benign. Use sqlite3Malloc()/memset(0) instead of 127 ** sqlite3MallocZero() to make the allocation, as sqlite3MallocZero()128 ** only zeroes the requested number of bytes whereas this module will129 ** use the actual amount of space allocated for the hash table (which130 ** may be larger than the requested amount).131 */132 sqlite3BeginBenignMalloc();133 new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );134 sqlite3EndBenignMalloc();135 136 if( new_ht==0 ) return 0;137 sqlite3_free(pH->ht);138 pH->ht = new_ht;139 pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht);140 memset(new_ht, 0, new_size*sizeof(struct _ht));141 for(elem=pH->first, pH->first=0; elem; elem = next_elem){142 next_elem = elem->next;143 insertElement(pH, &new_ht[elem->h % new_size], elem);144 }145 return 1;146}147 148/* This function (for internal use only) locates an element in an149** hash table that matches the given key. If no element is found,150** a pointer to a static null element with HashElem.data==0 is returned.151** If pH is not NULL, then the hash for this key is written to *pH.152*/153static HashElem *findElementWithHash(154 const Hash *pH, /* The pH to be searched */155 const char *pKey, /* The key we are searching for */156 unsigned int *pHash /* Write the hash value here */157){158 HashElem *elem; /* Used to loop thru the element list */159 unsigned int count; /* Number of elements left to test */160 unsigned int h; /* The computed hash */161 static HashElem nullElement = { 0, 0, 0, 0, 0 };162 163 h = strHash(pKey);164 if( pH->ht ){ /*OPTIMIZATION-IF-TRUE*/165 struct _ht *pEntry;166 pEntry = &pH->ht[h % pH->htsize];167 elem = pEntry->chain;168 count = pEntry->count;169 }else{170 elem = pH->first;171 count = pH->count;172 }173 if( pHash ) *pHash = h;174 while( count ){175 assert( elem!=0 );176 if( h==elem->h && sqlite3StrICmp(elem->pKey,pKey)==0 ){ 177 return elem;178 }179 elem = elem->next;180 count--;181 }182 return &nullElement;183}184 185/* Remove a single entry from the hash table given a pointer to that186** element and a hash on the element's key.187*/188static void removeElement(189 Hash *pH, /* The pH containing "elem" */190 HashElem *elem /* The element to be removed from the pH */191){192 struct _ht *pEntry;193 if( elem->prev ){194 elem->prev->next = elem->next; 195 }else{196 pH->first = elem->next;197 }198 if( elem->next ){199 elem->next->prev = elem->prev;200 }201 if( pH->ht ){202 pEntry = &pH->ht[elem->h % pH->htsize];203 if( pEntry->chain==elem ){204 pEntry->chain = elem->next;205 }206 assert( pEntry->count>0 );207 pEntry->count--;208 }209 sqlite3_free( elem );210 pH->count--;211 if( pH->count==0 ){212 assert( pH->first==0 );213 assert( pH->count==0 );214 sqlite3HashClear(pH);215 }216}217 218/* Attempt to locate an element of the hash table pH with a key219** that matches pKey. Return the data for this element if it is220** found, or NULL if there is no match.221*/222void *sqlite3HashFind(const Hash *pH, const char *pKey){223 assert( pH!=0 );224 assert( pKey!=0 );225 return findElementWithHash(pH, pKey, 0)->data;226}227 228/* Insert an element into the hash table pH. The key is pKey229** and the data is "data".230**231** If no element exists with a matching key, then a new232** element is created and NULL is returned.233**234** If another element already exists with the same key, then the235** new data replaces the old data and the old data is returned.236** The key is not copied in this instance. If a malloc fails, then237** the new data is returned and the hash table is unchanged.238**239** If the "data" parameter to this function is NULL, then the240** element corresponding to "key" is removed from the hash table.241*/242void *sqlite3HashInsert(Hash *pH, const char *pKey, void *data){243 unsigned int h; /* the hash of the key modulo hash table size */244 HashElem *elem; /* Used to loop thru the element list */245 HashElem *new_elem; /* New element added to the pH */246 247 assert( pH!=0 );248 assert( pKey!=0 );249 elem = findElementWithHash(pH,pKey,&h);250 if( elem->data ){251 void *old_data = elem->data;252 if( data==0 ){253 removeElement(pH,elem);254 }else{255 elem->data = data;256 elem->pKey = pKey;257 }258 return old_data;259 }260 if( data==0 ) return 0;261 new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) );262 if( new_elem==0 ) return data;263 new_elem->pKey = pKey;264 new_elem->h = h;265 new_elem->data = data;266 pH->count++;267 if( pH->count>=5 && pH->count > 2*pH->htsize ){268 rehash(pH, pH->count*3);269 }270 insertElement(pH, pH->ht ? &pH->ht[new_elem->h % pH->htsize] : 0, new_elem);271 return 0;272}273 274