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Simplifications to the symbol table implementation in hash.c. For very small

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symbol tables (less than 10 entries) a simple linked list is used instead
of a hash table.  Number of hash table buckets is limited to prevent large
allocations. (CVS 6559)

FossilOrigin-Name: 5c737835dec9e6038b304c198aa14337a6f23c1c
This commit is contained in:
drh
2009-04-28 15:43:45 +00:00
parent ebb329397c
commit 8a1e594c9f
6 changed files with 124 additions and 109 deletions
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25
src/hash.h
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@@ -12,7 +12,7 @@
** This is the header file for the generic hash-table implemenation
** used in SQLite.
**
** $Id: hash.h,v 1.12 2008/10/10 17:41:29 drh Exp $
** $Id: hash.h,v 1.13 2009/04/28 15:43:45 drh Exp $
*/
#ifndef _SQLITE_HASH_H_
#define _SQLITE_HASH_H_
@@ -25,12 +25,25 @@ typedef struct HashElem HashElem;
** 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, many of the "procedures" and "functions" for modifying and
** 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 copyKey: 1; /* True if copy of key made on insert */
unsigned int copyKey : 1; /* True if copy of key made on insert */
unsigned int htsize : 31; /* Number of buckets in the hash table */
unsigned int count; /* Number of entries in this table */
HashElem *first; /* The first element of the array */
@@ -76,12 +89,12 @@ void sqlite3HashClear(Hash*);
#define sqliteHashFirst(H) ((H)->first)
#define sqliteHashNext(E) ((E)->next)
#define sqliteHashData(E) ((E)->data)
#define sqliteHashKey(E) ((E)->pKey)
#define sqliteHashKeysize(E) ((E)->nKey)
/* #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)
/* #define sqliteHashCount(H) ((H)->count) // NOT USED */
#endif /* _SQLITE_HASH_H_ */