text: /*
  ** 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.
  **
  ** $Id: hash.c,v 1.16 2005/01/31 12:56:44 danielk1977 Exp $
  */
  #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.
  ** keyClass is one of the constants SQLITE_HASH_INT, SQLITE_HASH_POINTER,
  ** SQLITE_HASH_BINARY, or SQLITE_HASH_STRING.  The value of keyClass 
  ** determines what kind of key the hash table will use.  "copyKey" is
  ** true if the hash table should make its own private copy of keys and
  ** false if it should just use the supplied pointer.  CopyKey only makes
  ** sense for SQLITE_HASH_STRING and SQLITE_HASH_BINARY and is ignored
  ** for other key classes.
  */
  void sqlite3HashInit(Hash *pNew, int keyClass, int copyKey){
    assert( pNew!=0 );
    assert( keyClass>=SQLITE_HASH_STRING && keyClass<=SQLITE_HASH_BINARY );
    pNew->keyClass = keyClass;
  #if 0
    if( keyClass==SQLITE_HASH_POINTER || keyClass==SQLITE_HASH_INT ) copyKey = 0;
  #endif
    pNew->copyKey = copyKey;
    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;
    if( pH->ht ) sqliteFree(pH->ht);
    pH->ht = 0;
    pH->htsize = 0;
    while( elem ){
      HashElem *next_elem = elem->next;
      if( pH->copyKey && elem->pKey ){
        sqliteFree(elem->pKey);
      }
      sqliteFree(elem);
      elem = next_elem;
    }
    pH->count = 0;
  }
  
  #if 0 /* NOT USED */
  /*
  ** Hash and comparison functions when the mode is SQLITE_HASH_INT
  */
  static int intHash(const void *pKey, int nKey){
    return nKey ^ (nKey<<8) ^ (nKey>>8);
  }
  static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){
    return n2 - n1;
  }
  #endif
  
  #if 0 /* NOT USED */
  /*
  ** Hash and comparison functions when the mode is SQLITE_HASH_POINTER
  */
  static int ptrHash(const void *pKey, int nKey){
    uptr x = Addr(pKey);
    return x ^ (x<<8) ^ (x>>8);
  }
  static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){
    if( pKey1==pKey2 ) return 0;
    if( pKey1<pKey2 ) return -1;
    return 1;
  }
  #endif
  
  /*
  ** Hash and comparison functions when the mode is SQLITE_HASH_STRING
  */
  static int strHash(const void *pKey, int nKey){
    const char *z = (const char *)pKey;
    int h = 0;
    if( nKey<=0 ) nKey = strlen(z);
    while( nKey > 0  ){
      h = (h<<3) ^ h ^ sqlite3UpperToLower[(unsigned char)*z++];
      nKey--;
    }
    return h & 0x7fffffff;
  }
  static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
    if( n1!=n2 ) return 1;
    return sqlite3StrNICmp((const char*)pKey1,(const char*)pKey2,n1);
  }
  
  /*
  ** Hash and comparison functions when the mode is SQLITE_HASH_BINARY
  */
  static int binHash(const void *pKey, int nKey){
    int h = 0;
    const char *z = (const char *)pKey;
    while( nKey-- > 0 ){
      h = (h<<3) ^ h ^ *(z++);
    }
    return h & 0x7fffffff;
  }
  static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){
    if( n1!=n2 ) return 1;
    return memcmp(pKey1,pKey2,n1);
  }
  
  /*
  ** Return a pointer to the appropriate hash function given the key class.
  **
  ** The C syntax in this function definition may be unfamilar to some 
  ** programmers, so we provide the following additional explanation:
  **
  ** The name of the function is "hashFunction".  The function takes a
  ** single parameter "keyClass".  The return value of hashFunction()
  ** is a pointer to another function.  Specifically, the return value
  ** of hashFunction() is a pointer to a function that takes two parameters
  ** with types "const void*" and "int" and returns an "int".
  */
  static int (*hashFunction(int keyClass))(const void*,int){
  #if 0  /* HASH_INT and HASH_POINTER are never used */
    switch( keyClass ){
      case SQLITE_HASH_INT:     return &intHash;
      case SQLITE_HASH_POINTER: return &ptrHash;
      case SQLITE_HASH_STRING:  return &strHash;
      case SQLITE_HASH_BINARY:  return &binHash;;
      default: break;
    }
    return 0;
  #else
    if( keyClass==SQLITE_HASH_STRING ){
      return &strHash;
    }else{
      assert( keyClass==SQLITE_HASH_BINARY );
      return &binHash;
    }
  #endif
  }
  
  /*
  ** Return a pointer to the appropriate hash function given the key class.
  **
  ** For help in interpreted the obscure C code in the function definition,
  ** see the header comment on the previous function.
  */
  static int (*compareFunction(int keyClass))(const void*,int,const void*,int){
  #if 0 /* HASH_INT and HASH_POINTER are never used */
    switch( keyClass ){
      case SQLITE_HASH_INT:     return &intCompare;
      case SQLITE_HASH_POINTER: return &ptrCompare;
      case SQLITE_HASH_STRING:  return &strCompare;
      case SQLITE_HASH_BINARY:  return &binCompare;
      default: break;
    }
    return 0;
  #else
    if( keyClass==SQLITE_HASH_STRING ){
      return &strCompare;
    }else{
      assert( keyClass==SQLITE_HASH_BINARY );
      return &binCompare;
    }
  #endif
  }
  
  /* Link an element into the hash table
  */
  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 */
    pHead = pEntry->chain;
    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;
    }
    pEntry->count++;
    pEntry->chain = pNew;
  }
  
  
  /* Resize the hash table so that it cantains "new_size" buckets.
  ** "new_size" must be a power of 2.  The hash table might fail 
  ** to resize if sqliteMalloc() fails.
  */
  static void rehash(Hash *pH, int new_size){
    struct _ht *new_ht;            /* The new hash table */
    HashElem *elem, *next_elem;    /* For looping over existing elements */
    int (*xHash)(const void*,int); /* The hash function */
  
    assert( (new_size & (new_size-1))==0 );
    new_ht = (struct _ht *)sqliteMalloc( new_size*sizeof(struct _ht) );
    if( new_ht==0 ) return;
    if( pH->ht ) sqliteFree(pH->ht);
    pH->ht = new_ht;
    pH->htsize = new_size;
    xHash = hashFunction(pH->keyClass);
    for(elem=pH->first, pH->first=0; elem; elem = next_elem){
      int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);
      next_elem = elem->next;
      insertElement(pH, &new_ht[h], elem);
    }
  }
  
  /* This function (for internal use only) locates an element in an
  ** hash table that matches the given key.  The hash for this key has
  ** already been computed and is passed as the 4th parameter.
  */
  static HashElem *findElementGivenHash(
    const Hash *pH,     /* The pH to be searched */
    const void *pKey,   /* The key we are searching for */
    int nKey,
    int h               /* The hash for this key. */
  ){
    HashElem *elem;                /* Used to loop thru the element list */
    int count;                     /* Number of elements left to test */
    int (*xCompare)(const void*,int,const void*,int);  /* comparison function */
  
    if( pH->ht ){
      struct _ht *pEntry = &pH->ht[h];
      elem = pEntry->chain;
      count = pEntry->count;
      xCompare = compareFunction(pH->keyClass);
      while( count-- && elem ){
        if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==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 */
    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;
    }
    pEntry = &pH->ht[h];
    if( pEntry->chain==elem ){
      pEntry->chain = elem->next;
    }
    pEntry->count--;
    if( pEntry->count<=0 ){
      pEntry->chain = 0;
    }
    if( pH->copyKey && elem->pKey ){
      sqliteFree(elem->pKey);
    }
    sqliteFree( elem );
    pH->count--;
  }
  
  /* Attempt to locate an element of the hash table pH with a key
  ** that matches pKey,nKey.  Return the data for this element if it is
  ** found, or NULL if there is no match.
  */
  void *sqlite3HashFind(const Hash *pH, const void *pKey, int nKey){
    int h;             /* A hash on key */
    HashElem *elem;    /* The element that matches key */
    int (*xHash)(const void*,int);  /* The hash function */
  
    if( pH==0 || pH->ht==0 ) return 0;
    xHash = hashFunction(pH->keyClass);
    assert( xHash!=0 );
    h = (*xHash)(pKey,nKey);
    assert( (pH->htsize & (pH->htsize-1))==0 );
    elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));
    return elem ? elem->data : 0;
  }
  
  /* Insert an element into the hash table pH.  The key is pKey,nKey
  ** and the data is "data".
  **
  ** If no element exists with a matching key, then a new
  ** element is created.  A copy of the key is made if the copyKey
  ** flag is set.  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 void *pKey, int nKey, void *data){
    int hraw;             /* Raw hash value of the key */
    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 */
    int (*xHash)(const void*,int);  /* The hash function */
  
    assert( pH!=0 );
    xHash = hashFunction(pH->keyClass);
    assert( xHash!=0 );
    hraw = (*xHash)(pKey, nKey);
    assert( (pH->htsize & (pH->htsize-1))==0 );
    h = hraw & (pH->htsize-1);
    elem = findElementGivenHash(pH,pKey,nKey,h);
    if( elem ){
      void *old_data = elem->data;
      if( data==0 ){
        removeElementGivenHash(pH,elem,h);
      }else{
        elem->data = data;
      }
      return old_data;
    }
    if( data==0 ) return 0;
    new_elem = (HashElem*)sqliteMalloc( sizeof(HashElem) );
    if( new_elem==0 ) return data;
    if( pH->copyKey && pKey!=0 ){
      new_elem->pKey = sqliteMallocRaw( nKey );
      if( new_elem->pKey==0 ){
        sqliteFree(new_elem);
        return data;
      }
      memcpy((void*)new_elem->pKey, pKey, nKey);
    }else{
      new_elem->pKey = (void*)pKey;
    }
    new_elem->nKey = nKey;
    pH->count++;
    if( pH->htsize==0 ){
      rehash(pH,8);
      if( pH->htsize==0 ){
        pH->count = 0;
        sqliteFree(new_elem);
        return data;
      }
    }
    if( pH->count > pH->htsize ){
      rehash(pH,pH->htsize*2);
    }
    assert( pH->htsize>0 );
    assert( (pH->htsize & (pH->htsize-1))==0 );
    h = hraw & (pH->htsize-1);
    insertElement(pH, &pH->ht[h], new_elem);
    new_elem->data = data;
    return 0;
  }
  