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Diffstat (limited to 'src/hash.c')
| -rw-r--r-- | src/hash.c | 270 |
1 files changed, 270 insertions, 0 deletions
diff --git a/src/hash.c b/src/hash.c new file mode 100644 index 0000000..8ec043f --- /dev/null +++ b/src/hash.c @@ -0,0 +1,270 @@ +/* +** 2001 September 22 +** +** The author disclaims copyright to this source code. In place of +** a legal notice, here is a blessing: +** +** May you do good and not evil. +** May you find forgiveness for yourself and forgive others. +** May you share freely, never taking more than you give. +** +************************************************************************* +** This is the implementation of generic hash-tables +** used in SQLite. +*/ +#include "sqliteInt.h" +#include <assert.h> + +/* Turn bulk memory into a hash table object by initializing the +** fields of the Hash structure. +** +** "pNew" is a pointer to the hash table that is to be initialized. +*/ +void sqlite3HashInit(Hash *pNew){ + assert( pNew!=0 ); + pNew->first = 0; + pNew->count = 0; + pNew->htsize = 0; + pNew->ht = 0; +} + +/* Remove all entries from a hash table. Reclaim all memory. +** Call this routine to delete a hash table or to reset a hash table +** to the empty state. +*/ +void sqlite3HashClear(Hash *pH){ + HashElem *elem; /* For looping over all elements of the table */ + + assert( pH!=0 ); + elem = pH->first; + pH->first = 0; + sqlite3_free(pH->ht); + pH->ht = 0; + pH->htsize = 0; + while( elem ){ + HashElem *next_elem = elem->next; + sqlite3_free(elem); + elem = next_elem; + } + pH->count = 0; +} + +/* +** The hashing function. +*/ +static unsigned int strHash(const char *z){ + unsigned int h = 0; + unsigned char c; + while( (c = (unsigned char)*z++)!=0 ){ /*OPTIMIZATION-IF-TRUE*/ + /* Knuth multiplicative hashing. (Sorting & Searching, p. 510). + ** 0x9e3779b1 is 2654435761 which is the closest prime number to + ** (2**32)*golden_ratio, where golden_ratio = (sqrt(5) - 1)/2. */ + h += sqlite3UpperToLower[c]; + h *= 0x9e3779b1; + } + return h; +} + + +/* Link pNew element into the hash table pH. If pEntry!=0 then also +** insert pNew into the pEntry hash bucket. +*/ +static void insertElement( + Hash *pH, /* The complete hash table */ + struct _ht *pEntry, /* The entry into which pNew is inserted */ + HashElem *pNew /* The element to be inserted */ +){ + HashElem *pHead; /* First element already in pEntry */ + if( pEntry ){ + pHead = pEntry->count ? pEntry->chain : 0; + pEntry->count++; + pEntry->chain = pNew; + }else{ + pHead = 0; + } + if( pHead ){ + pNew->next = pHead; + pNew->prev = pHead->prev; + if( pHead->prev ){ pHead->prev->next = pNew; } + else { pH->first = pNew; } + pHead->prev = pNew; + }else{ + pNew->next = pH->first; + if( pH->first ){ pH->first->prev = pNew; } + pNew->prev = 0; + pH->first = pNew; + } +} + + +/* Resize the hash table so that it contains "new_size" buckets. +** +** The hash table might fail to resize if sqlite3_malloc() fails or +** if the new size is the same as the prior size. +** Return TRUE if the resize occurs and false if not. +*/ +static int rehash(Hash *pH, unsigned int new_size){ + struct _ht *new_ht; /* The new hash table */ + HashElem *elem, *next_elem; /* For looping over existing elements */ + +#if SQLITE_MALLOC_SOFT_LIMIT>0 + if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){ + new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht); + } + if( new_size==pH->htsize ) return 0; +#endif + + /* The inability to allocates space for a larger hash table is + ** a performance hit but it is not a fatal error. So mark the + ** allocation as a benign. Use sqlite3Malloc()/memset(0) instead of + ** sqlite3MallocZero() to make the allocation, as sqlite3MallocZero() + ** only zeroes the requested number of bytes whereas this module will + ** use the actual amount of space allocated for the hash table (which + ** may be larger than the requested amount). + */ + sqlite3BeginBenignMalloc(); + new_ht = (struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) ); + sqlite3EndBenignMalloc(); + + if( new_ht==0 ) return 0; + sqlite3_free(pH->ht); + pH->ht = new_ht; + pH->htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht); + memset(new_ht, 0, new_size*sizeof(struct _ht)); + for(elem=pH->first, pH->first=0; elem; elem = next_elem){ + unsigned int h = strHash(elem->pKey) % new_size; + next_elem = elem->next; + insertElement(pH, &new_ht[h], elem); + } + return 1; +} + +/* This function (for internal use only) locates an element in an +** hash table that matches the given key. If no element is found, +** a pointer to a static null element with HashElem.data==0 is returned. +** If pH is not NULL, then the hash for this key is written to *pH. +*/ +static HashElem *findElementWithHash( + const Hash *pH, /* The pH to be searched */ + const char *pKey, /* The key we are searching for */ + unsigned int *pHash /* Write the hash value here */ +){ + HashElem *elem; /* Used to loop thru the element list */ + unsigned int count; /* Number of elements left to test */ + unsigned int h; /* The computed hash */ + static HashElem nullElement = { 0, 0, 0, 0 }; + + if( pH->ht ){ /*OPTIMIZATION-IF-TRUE*/ + struct _ht *pEntry; + h = strHash(pKey) % pH->htsize; + pEntry = &pH->ht[h]; + elem = pEntry->chain; + count = pEntry->count; + }else{ + h = 0; + elem = pH->first; + count = pH->count; + } + if( pHash ) *pHash = h; + while( count ){ + assert( elem!=0 ); + if( sqlite3StrICmp(elem->pKey,pKey)==0 ){ + return elem; + } + elem = elem->next; + count--; + } + return &nullElement; +} + +/* Remove a single entry from the hash table given a pointer to that +** element and a hash on the element's key. +*/ +static void removeElementGivenHash( + Hash *pH, /* The pH containing "elem" */ + HashElem* elem, /* The element to be removed from the pH */ + unsigned int h /* Hash value for the element */ +){ + struct _ht *pEntry; + if( elem->prev ){ + elem->prev->next = elem->next; + }else{ + pH->first = elem->next; + } + if( elem->next ){ + elem->next->prev = elem->prev; + } + if( pH->ht ){ + pEntry = &pH->ht[h]; + if( pEntry->chain==elem ){ + pEntry->chain = elem->next; + } + assert( pEntry->count>0 ); + pEntry->count--; + } + sqlite3_free( elem ); + pH->count--; + if( pH->count==0 ){ + assert( pH->first==0 ); + assert( pH->count==0 ); + sqlite3HashClear(pH); + } +} + +/* Attempt to locate an element of the hash table pH with a key +** that matches pKey. Return the data for this element if it is +** found, or NULL if there is no match. +*/ +void *sqlite3HashFind(const Hash *pH, const char *pKey){ + assert( pH!=0 ); + assert( pKey!=0 ); + return findElementWithHash(pH, pKey, 0)->data; +} + +/* Insert an element into the hash table pH. The key is pKey +** and the data is "data". +** +** If no element exists with a matching key, then a new +** element is created and NULL is returned. +** +** If another element already exists with the same key, then the +** new data replaces the old data and the old data is returned. +** The key is not copied in this instance. If a malloc fails, then +** the new data is returned and the hash table is unchanged. +** +** If the "data" parameter to this function is NULL, then the +** element corresponding to "key" is removed from the hash table. +*/ +void *sqlite3HashInsert(Hash *pH, const char *pKey, void *data){ + unsigned int h; /* the hash of the key modulo hash table size */ + HashElem *elem; /* Used to loop thru the element list */ + HashElem *new_elem; /* New element added to the pH */ + + assert( pH!=0 ); + assert( pKey!=0 ); + elem = findElementWithHash(pH,pKey,&h); + if( elem->data ){ + void *old_data = elem->data; + if( data==0 ){ + removeElementGivenHash(pH,elem,h); + }else{ + elem->data = data; + elem->pKey = pKey; + } + return old_data; + } + if( data==0 ) return 0; + new_elem = (HashElem*)sqlite3Malloc( sizeof(HashElem) ); + if( new_elem==0 ) return data; + new_elem->pKey = pKey; + new_elem->data = data; + pH->count++; + if( pH->count>=10 && pH->count > 2*pH->htsize ){ + if( rehash(pH, pH->count*2) ){ + assert( pH->htsize>0 ); + h = strHash(pKey) % pH->htsize; + } + } + insertElement(pH, pH->ht ? &pH->ht[h] : 0, new_elem); + return 0; +} |