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sqlite3

    1: /*
    2: ** 2001 September 22
    3: **
    4: ** The author disclaims copyright to this source code.  In place of
    5: ** 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 header file for the generic hash-table implemenation
   13: ** used in SQLite.
   14: */
   15: #ifndef _SQLITE_HASH_H_
   16: #define _SQLITE_HASH_H_
   17: 
   18: /* Forward declarations of structures. */
   19: typedef struct Hash Hash;
   20: typedef struct HashElem HashElem;
   21: 
   22: /* A complete hash table is an instance of the following structure.
   23: ** The internals of this structure are intended to be opaque -- client
   24: ** code should not attempt to access or modify the fields of this structure
   25: ** directly.  Change this structure only by using the routines below.
   26: ** However, some of the "procedures" and "functions" for modifying and
   27: ** accessing this structure are really macros, so we can't really make
   28: ** this structure opaque.
   29: **
   30: ** All elements of the hash table are on a single doubly-linked list.
   31: ** Hash.first points to the head of this list.
   32: **
   33: ** There are Hash.htsize buckets.  Each bucket points to a spot in
   34: ** the global doubly-linked list.  The contents of the bucket are the
   35: ** element pointed to plus the next _ht.count-1 elements in the list.
   36: **
   37: ** Hash.htsize and Hash.ht may be zero.  In that case lookup is done
   38: ** by a linear search of the global list.  For small tables, the 
   39: ** Hash.ht table is never allocated because if there are few elements
   40: ** in the table, it is faster to do a linear search than to manage
   41: ** the hash table.
   42: */
   43: struct Hash {
   44:   unsigned int htsize;      /* Number of buckets in the hash table */
   45:   unsigned int count;       /* Number of entries in this table */
   46:   HashElem *first;          /* The first element of the array */
   47:   struct _ht {              /* the hash table */
   48:     int count;                 /* Number of entries with this hash */
   49:     HashElem *chain;           /* Pointer to first entry with this hash */
   50:   } *ht;
   51: };
   52: 
   53: /* Each element in the hash table is an instance of the following 
   54: ** structure.  All elements are stored on a single doubly-linked list.
   55: **
   56: ** Again, this structure is intended to be opaque, but it can't really
   57: ** be opaque because it is used by macros.
   58: */
   59: struct HashElem {
   60:   HashElem *next, *prev;       /* Next and previous elements in the table */
   61:   void *data;                  /* Data associated with this element */
   62:   const char *pKey; int nKey;  /* Key associated with this element */
   63: };
   64: 
   65: /*
   66: ** Access routines.  To delete, insert a NULL pointer.
   67: */
   68: void sqlite3HashInit(Hash*);
   69: void *sqlite3HashInsert(Hash*, const char *pKey, int nKey, void *pData);
   70: void *sqlite3HashFind(const Hash*, const char *pKey, int nKey);
   71: void sqlite3HashClear(Hash*);
   72: 
   73: /*
   74: ** Macros for looping over all elements of a hash table.  The idiom is
   75: ** like this:
   76: **
   77: **   Hash h;
   78: **   HashElem *p;
   79: **   ...
   80: **   for(p=sqliteHashFirst(&h); p; p=sqliteHashNext(p)){
   81: **     SomeStructure *pData = sqliteHashData(p);
   82: **     // do something with pData
   83: **   }
   84: */
   85: #define sqliteHashFirst(H)  ((H)->first)
   86: #define sqliteHashNext(E)   ((E)->next)
   87: #define sqliteHashData(E)   ((E)->data)
   88: /* #define sqliteHashKey(E)    ((E)->pKey) // NOT USED */
   89: /* #define sqliteHashKeysize(E) ((E)->nKey)  // NOT USED */
   90: 
   91: /*
   92: ** Number of entries in a hash table
   93: */
   94: /* #define sqliteHashCount(H)  ((H)->count) // NOT USED */
   95: 
   96: #endif /* _SQLITE_HASH_H_ */