src/hash.h

   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 implementation
  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_ */