Initial check in. Preliminary development stage.
From-SVN: r46
This commit is contained in:
Dennis Glatting
parent
e545f2b026
commit
4217c4568b
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/* -*-c-*-
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* This file contains the hashing implementation.
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*
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$Header$
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$Author$
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$Date$
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$Log$
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*/
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#include <hash.h>
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#include <ObjC.h>
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#include <assert.h>
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#include <libc.h>
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#include <math.h>
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/* Local forward decl. */
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u_int hashValue( Cache_t, void* );
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Cache_t hash_new( u_int numberOfBuckets ) {
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Cache_t retCache;
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int i;
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assert( numberOfBuckets );
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/* Allocate the cache
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structure. calloc() insures
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its initialization for
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default values. */
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retCache = calloc( 1, sizeof( Cache ));
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assert( retCache );
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/* Allocate the array of
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buckets for the cache.
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calloc() initializes all of
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the pointers to NULL. */
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retCache->theNodeTable = calloc( numberOfBuckets, sizeof( CacheNode_t ));
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assert( retCache->theNodeTable );
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retCache->numberOfBuckets = numberOfBuckets;
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/* Calculate the number of
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bits required to represent
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the hash mask. */
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retCache->numberOfMaskBits =
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ceil( log( retCache->numberOfBuckets ) / log( 2 ));
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/* Form a bit mask for the
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hash. */
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for( i = 0; i < retCache->numberOfMaskBits; ++i )
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retCache->mask = ( retCache->mask << 1 ) | 0x01 ;
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assert( retCache->numberOfMaskBits );
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assert( retCache->mask );
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return retCache;
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}
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void hash_delete( Cache_t theCache ) {
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void* aNode;
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/* Purge all key/value pairs
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from the table. */
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while( aNode = hash_next( theCache, NULL ))
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hash_remove( theCache, aNode );
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/* Release the array of nodes
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and the cache itself. */
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free( theCache->theNodeTable );
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free( theCache );
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}
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void hash_add( Cache_t theCache, void* aKey, void* aValue ) {
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u_int indx = hashValue( theCache, aKey );
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CacheNode_t aCacheNode = calloc( 1, sizeof( CacheNode ));
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assert( aCacheNode );
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/* Initialize the new node. */
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aCacheNode->theKey = aKey;
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aCacheNode->theValue = aValue;
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aCacheNode->nextNode = ( *theCache->theNodeTable )[ indx ];
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/* Debugging.
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Check the list for another
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key. */
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#ifdef DEBUG
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{ CacheNode_t checkHashNode = ( *theCache->theNodeTable )[ indx ];
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while( checkHashNode ) {
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assert( checkHashNode->theKey != aKey );
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checkHashNode = checkHashNode->nextNode;
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}
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}
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/* Install the node as the
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first element on the list. */
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( *theCache->theNodeTable )[ indx ] = aCacheNode;
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#endif
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}
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void hash_remove( Cache_t theCache, void* aKey ) {
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u_int indx = hashValue( theCache, aKey );
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CacheNode_t aCacheNode = ( *theCache->theNodeTable )[ indx ];
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/* We assume there is an entry
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in the table. Error if it
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is not. */
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assert( aCacheNode );
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/* Special case. First element
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is the key/value pair to be
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removed. */
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if( aCacheNode->theKey == aKey ) {
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( *theCache->theNodeTable )[ indx ] = aCacheNode->nextNode;
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free( aCacheNode );
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} else {
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/* Otherwise, find the hash
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entry. */
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CacheNode_t prevHashNode = aCacheNode;
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BOOL removed = NO;
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do {
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if( aCacheNode->theKey == aKey ) {
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prevHashNode->nextNode = aCacheNode->nextNode, removed = YES;
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free( aCacheNode );
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} else
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prevHashNode = aCacheNode, aCacheNode = aCacheNode->nextNode;
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} while( !removed && aCacheNode );
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assert( removed );
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}
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}
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void* hash_value_for_key( Cache_t theCache, void* aKey ) {
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u_int indx = hashValue( theCache, aKey );
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CacheNode_t aCacheNode = ( *theCache->theNodeTable )[ indx ];
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void* retVal = NULL;
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if( aCacheNode ) {
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BOOL found = NO;
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do {
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if( aCacheNode->theKey == aKey )
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retVal = aCacheNode->theValue, found = YES;
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else
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aCacheNode = aCacheNode->nextNode;
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} while( !found && aCacheNode );
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}
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return retVal;
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}
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CacheNode_t hash_next( Cache_t theCache, CacheNode_t aCacheNode ) {
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CacheNode_t theCacheNode = aCacheNode;
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/* If the scan is being started
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then reset the last node
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visitied pointer and bucket
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index. */
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if( !theCacheNode )
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theCache->lastBucket = 0;
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/* If there is a node visited
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last then check for another
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entry in the same bucket;
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Otherwise step to the next
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bucket. */
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if( theCacheNode )
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if( theCacheNode->nextNode )
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/* There is a node which
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follows the last node
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returned. Step to that node
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and retun it. */
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return theCacheNode->nextNode;
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else
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++theCache->lastBucket;
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/* If the list isn't exhausted
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then search the buckets for
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other nodes. */
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if( theCache->lastBucket < theCache->numberOfBuckets ) {
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/* Scan the remainder of the
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buckets looking for an entry
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at the head of the list.
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Return the first item
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found. */
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while( theCache->lastBucket < theCache->numberOfBuckets )
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if(( *theCache->theNodeTable )[ theCache->lastBucket ])
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return ( *theCache->theNodeTable )[ theCache->lastBucket ];
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else
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++theCache->lastBucket;
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/* No further nodes were found
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in the hash table. */
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return NULL;
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} else
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return NULL;
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}
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u_int hashValue( Cache_t theCache, void* aKey ) {
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u_int hash = 0;
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int i;
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assert( theCache->numberOfMaskBits );
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for( i = 0; i < ( sizeof( aKey ) * 8 ); i += theCache->numberOfMaskBits )
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hash ^= (( u_int )aKey ) >> i ;
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return ( hash & theCache->mask ) % theCache->numberOfBuckets;
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}
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@ -0,0 +1,134 @@
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/* -*-c-*-
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* This is a general purpose hash object.
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*
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* The hash object used throughout the run-time
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* is an integer hash. The key and data is of type
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* void*. The hashing function converts the key to
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* an integer and computes it hash value.
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*
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$Header$
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$Author$
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$Date$
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$Log$
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*/
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#ifndef _hash_INCLUDE_GNU
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#define _hash_INCLUDE_GNU
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/* If someone is using a c++
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compiler then adjust the
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types in the file back
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to C. */
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <sys/types.h>
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/*
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* This data structure is used to hold items
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* stored in a hash table. Each node holds
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* a key/value pair.
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*
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* Items in the cache are really of type void*.
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*/
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typedef struct cache_node {
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struct cache_node* nextNode; /* Pointer to next entry on
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the list. NULL indicates
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end of list. */
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void* theKey; /* Key used to locate the
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value. Used to locate
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value when more than one
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key computes the same hash
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value. */
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void* theValue; /* Value stored for the
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key. */
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} CacheNode, *CacheNode_t;
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/*
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* This data structure is the cache.
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*
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* It must be passed to all of the hashing routines
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* (except for new).
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*/
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typedef struct cache {
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/*
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* Variables used to implement the
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* hash itself.
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*/
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CacheNode_t (* theNodeTable )[]; /* Pointer to an array of
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hash nodes. */
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u_int numberOfBuckets, /* Number of buckets
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allocated for the hash
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table (number of array
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entries allocated for
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"theCache"). */
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mask, /* Mask used when computing
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a hash value. The number
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of bits set in the mask
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is contained in the next
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member variable. */
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numberOfMaskBits; /* Number of bits used for
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the mask. Useful for
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efficient hash value
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calculation. */
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/*
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* Variables used to implement indexing
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* through the hash table.
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*/
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u_int lastBucket; /* Tracks which entry in the
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array where the last value
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was returned. */
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} Cache, *Cache_t;
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/* Prototypes for hash
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functions. */
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/* Allocate and initialize
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a hash table. Hash table
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size taken as a parameter.
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A value of 0 is not
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allowed. */
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Cache_t hash_new( u_int numberOfBuckets );
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/* Deallocate all of the
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hash nodes and the cache
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itself. */
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void hash_delete( Cache_t theCache );
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/* Add the key/value pair
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to the hash table. assert()
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if the key is already in
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the hash. */
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void hash_add( Cache_t theCache, void* aKey, void* aValue );
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/* Remove the key/value pair
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from the hash table.
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assert() if the key isn't
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in the table. */
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void hash_remove( Cache_t theCache, void* aKey );
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/* Given key, return its
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value. Return NULL if the
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key/value pair isn't in
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the hash. */
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void* hash_value_for_key( Cache_t theCache, void* aKey );
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/* Used to index through the
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hash table. Start with NULL
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to get the first entry.
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Successive calls pass the
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value returned previously.
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** Don't modify the hash
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during this operation ***
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Cache nodes are returned
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such that key or value can
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ber extracted. */
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CacheNode_t hash_next( Cache_t theCache, CacheNode_t aCacheNode );
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#ifdef __cplusplus
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}
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#endif
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#endif
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