[sql] Import reference version of SQLite 3.17..

third_party/sqlite/sqlite-src-3170000/src/hash.c

+/*
+** 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 cantains "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.  The hash for this key is
+** also computed and returned in the *pH parameter.
+*/
+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 */
+  int count;                     /* Number of elements left to test */
+  unsigned int h;                /* The computed hash */
+
+  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;
+  }
+  *pHash = h;
+  while( count-- ){
+    assert( elem!=0 );
+    if( sqlite3StrICmp(elem->pKey,pKey)==0 ){ 
+      return elem;
+    }
+    elem = elem->next;
+  }
+  return 0;
+}
+
+/* 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;
+    }
+    pEntry->count--;
+    assert( pEntry->count>=0 );
+  }
+  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){
+  HashElem *elem;    /* The element that matches key */
+  unsigned int h;    /* A hash on key */
+
+  assert( pH!=0 );
+  assert( pKey!=0 );
+  elem = findElementWithHash(pH, pKey, &h);
+  return elem ? elem->data : 0;
+}
+
+/* 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 ){
+    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;
+}