/*
** 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 header file for the generic hash-table implementation
** used in SQLite.
*/
#ifndef SQLITE_HASH_H
#define SQLITE_HASH_H

/* Forward declarations of structures. */
typedef struct Hash Hash;
typedef struct HashElem HashElem;

/* A complete hash table is an instance of the following structure.
** The internals of this structure are intended to be opaque -- client
** code should not attempt to access or modify the fields of this structure
** directly. Change this structure only by using the routines below.
** However, some of the "procedures" and "functions" for modifying and
** accessing this structure are really macros, so we can't really make
** this structure opaque.
**
** All elements of the hash table are on a single doubly-linked list.
** Hash.first points to the head of this list.
**
** There are Hash.htsize buckets. Each bucket points to a spot in
** the global doubly-linked list. The contents of the bucket are the
** element pointed to plus the next _ht.count-1 elements in the list.
**
** Hash.htsize and Hash.ht may be zero. In that case lookup is done
** by a linear search of the global list. For small tables, the 
** Hash.ht table is never allocated because if there are few elements
** in the table, it is faster to do a linear search than to manage
** the hash table.
*/
struct Hash {
 unsigned int htsize; /* Number of buckets in the hash table */
 unsigned int count; /* Number of entries in this table */
 HashElem *first; /* The first element of the array */
 struct _ht { /* the hash table */
 unsigned int count; /* Number of entries with this hash */
 HashElem *chain; /* Pointer to first entry with this hash */
 } *ht;
};

/* Each element in the hash table is an instance of the following 
** structure. All elements are stored on a single doubly-linked list.
**
** Again, this structure is intended to be opaque, but it can't really
** be opaque because it is used by macros.
*/
struct HashElem {
 HashElem *next, *prev; /* Next and previous elements in the table */
 void *data; /* Data associated with this element */
 const char *pKey; /* Key associated with this element */
};

/*
** Access routines. To delete, insert a NULL pointer.
*/
void sqlite3HashInit(Hash*);
void *sqlite3HashInsert(Hash*, const char *pKey, void *pData);
void *sqlite3HashFind(const Hash*, const char *pKey);
void sqlite3HashClear(Hash*);

/*
** Macros for looping over all elements of a hash table. The idiom is
** like this:
**
** Hash h;
** HashElem *p;
** ...
** for(p=sqliteHashFirst(&h); p; p=sqliteHashNext(p)){
** SomeStructure *pData = sqliteHashData(p);
** // do something with pData
** }
*/
#define sqliteHashFirst(H) ((H)->first)
#define sqliteHashNext(E) ((E)->next)
#define sqliteHashData(E) ((E)->data)
/* #define sqliteHashKey(E) ((E)->pKey) // NOT USED */
/* #define sqliteHashKeysize(E) ((E)->nKey) // NOT USED */

/*
** Number of entries in a hash table
*/
#define sqliteHashCount(H) ((H)->count)

#endif /* SQLITE_HASH_H */