windows-nt/Source/XPSP1/NT/windows/richedit/re30/hash.cpp

/*
 *	@doc	INTERNAL
 *
 *	@module HASH.C -- RTF control word cache |
 *		#ifdef'ed with RTF_HASHCACHE
 *		
 *	Owner: <nl>
 *		Jon Matousek <nl>
 *
 *	History: <nl>
 *		8/15/95		jonmat first hash-cache for RTF using Brent's Method.
 */
#include "_common.h"

#ifdef RTF_HASHCACHE
					 
#include "hash.h"

ASSERTDATA

extern KEYWORD		rgKeyword[];			// All of the RTF control words.

#define MAX_INAME	3

typedef struct {
	const KEYWORD	*token;
	BOOL			passBit;
} HashEntry;

static HashEntry	*(hashtbl[HASHSIZE]);
static HashEntry	*storage;				// Dynamically alloc for cKeywords.

BOOL				_rtfHashInited = FALSE;

static INT			HashKeyword_Key( const CHAR *szKeyword );

/*
 *	HashKeyword_Insert()
 *	
 *	@func
 *		Insert a KEYWORD into the RTF hash table.
 *	@comm
 *		This function uses the the % for MOD
 *		in order to validate MOD257.
 */
VOID HashKeyword_Insert (
	const KEYWORD *token )//@parm pointer to KEYWORD token to insert.
{
	TRACEBEGIN(TRCSUBSYSDISP, TRCSCOPEINTERN, "HashKeyword_Insert");

	INT			index, step, position,
				cost, source, sink, index1,
				step1, temp;
	
	BOOL		tmpPassBit;	
	
	static INT	totalKeys = 0;

	CHAR 		*szKeyword;
	
	HashEntry	*np;
	
	AssertSz ( _rtfHashInited, "forgot to call HashKeyword_Init()");
	AssertSz ( totalKeys <= HASHSIZE * 0.7, "prime not large enough to hold total keys");
	
	szKeyword = token->szKeyword;
	
	np = &storage[totalKeys++];
	np->token = token;

	index = HashKeyword_Key(szKeyword) % HASHSIZE;  // Get keys.
	step = 1 + (HashKeyword_Key(szKeyword) % (HASHSIZE-1));

	position = 1;
	cost = HASHSIZE;								// The max collisions for any.
	while(hashtbl[index]!=NULL)						// Find empty slot.
	{
		position++;									// How many collisions.

		// For the keyword stored here, calc # times before it is found.
		temp=1;
		step1= 1+(HashKeyword_Key(hashtbl[index]->token->szKeyword) % (HASHSIZE-1));
		index1= (index+step1)%HASHSIZE;
		while(hashtbl[index1] !=NULL)
		{
			index1=(index1+step1)%HASHSIZE;
			temp++;
		}
		
		// Incremental cost computation, minimizes average # of collisions
		//  for both keywords.
		if (cost>position+temp)
		{
			source=index;
			sink=index1;
			cost=position+temp;
		}
		
		// There will be something stored beyound here, set the passBit.
		hashtbl[index]->passBit=1;

		// Next index to search for empty slot.
		index=(index+step)%HASHSIZE;

	}
	
	if (position<=cost)
	{
		source=sink=index;
		cost=position;
	}
	hashtbl[sink] = hashtbl[source];
	hashtbl[source] = np;
	if (hashtbl[sink] && hashtbl[source])	// jOn hack, we didn't really
	{										//  want to swap pass bits.
		tmpPassBit = hashtbl[sink]->passBit;
		hashtbl[sink]->passBit = hashtbl[source]->passBit;
		hashtbl[source]->passBit = tmpPassBit;
	}

}

/*
 *	static HashKeyword_Key()
 *	
 *	@func
 *		Calculate the hash key.
 *	@comm
 *		Just add up the first few characters.
 *	@rdesc
 *		The hash Key for calculating the index and step.
 */
static INT HashKeyword_Key(
	const CHAR *szKeyword ) //@parm C string to create hash key for.
{
	TRACEBEGIN(TRCSUBSYSDISP, TRCSCOPEINTERN, "HashKeyword_Key");

	INT i, tot = 0;
	
	/* Just add up first few characters. */
	for (i = 0; i < MAX_INAME && *szKeyword; szKeyword++, i++)
			tot += (UCHAR) *szKeyword;
	return tot;
}	

/*
 *	HashKeyword_Fetch()
 *	
 *	@func
 *		Look up a KEYWORD with the given szKeyword.
 *	@devnote
 *		We have a hash table of size 257. This allows for
 *		the use of very fast routines to calculate a MOD 257.
 *		This gives us a significant increase in performance
 *		over a binary search.
 *	@rdesc
 *		A pointer to the KEYWORD, or NULL if not found.
 */
const KEYWORD *HashKeyword_Fetch (
	const CHAR *szKeyword ) //@parm C string to search for.
{
	TRACEBEGIN(TRCSUBSYSDISP, TRCSCOPEINTERN, "HashKeyword_Fetch");

	INT 		index, step;
	
	HashEntry *	hashTblPtr;

	BYTE *		pchCandidate;
	BYTE *		pchKeyword;
	
	INT			nComp;

	CHAR		firstChar;

	INT			hashKey;

	AssertSz( HASHSIZE == 257, "Remove custom MOD257.");
	
	firstChar = *szKeyword;
	hashKey = HashKeyword_Key(szKeyword);	// For calc'ing 'index' and 'step'
	
	//index = hashKey%HASHSIZE;				// First entry to search.
	index = MOD257(hashKey);				// This formula gives us 18% perf.

	hashTblPtr = hashtbl[index];			// Get first entry.
	if ( hashTblPtr != NULL )				// Something there?
	{
											// Compare 2 C strings.								
		pchCandidate = (BYTE *)hashTblPtr->token->szKeyword;
		if ( firstChar == *pchCandidate )
		{
			pchKeyword	 = (BYTE *)szKeyword;
			while (!(nComp = *pchKeyword - *pchCandidate)	// Be sure to match
				&& *pchKeyword)								//  terminating 0's
			{
				pchKeyword++;
				pchCandidate++;
			}
											// Matched?
			if ( 0 == nComp )
				return hashTblPtr->token;
		}
		
		if ( hashTblPtr->passBit==1 )		// passBit=>another entry to test
		{

			// step = 1+(hashKey%(HASHSIZE-1));// Calc 'step'
			step = 1 + MOD257_1(hashKey);

											// Get second entry to check.
			index += step;
			index = MOD257(index);
			hashTblPtr = hashtbl[index];

			while (hashTblPtr != NULL )		// While something there.
			{
											// Compare 2 C strings.								
				pchCandidate = (BYTE *)hashTblPtr->token->szKeyword;
				if ( firstChar == *pchCandidate )
				{
					pchKeyword	 = (BYTE *)szKeyword;
					while (!(nComp = *pchKeyword - *pchCandidate)
						&& *pchKeyword)
					{
						pchKeyword++;
						pchCandidate++;
					}
											// Matched?
					if ( 0 == nComp )
						return hashTblPtr->token;
				}

				if ( !hashTblPtr->passBit )// Done searching?
					break;
											// Get next entry.
				index += step;
				index = MOD257(index);
				hashTblPtr = hashtbl[index];
			}
		}
	}
	
	return NULL;
}

/*
 *	HashKeyword_Init()
 *	
 *	@func
 *		Load up and init the hash table with RTF control words.
 *	@devnote
 *		_rtfHashInited will be FALSE if anything here fails.
 */
VOID HashKeyword_Init( )
{
	TRACEBEGIN(TRCSUBSYSDISP, TRCSCOPEINTERN, "HashKeyword_Init");

	extern SHORT cKeywords;			// How many RTF keywords we currently recognize.

	INT i;

	AssertSz( _rtfHashInited == FALSE, "Only need to init this once.");

									// Create enough storage for cKeywords
	storage = (HashEntry *) PvAlloc( sizeof(HashEntry) * cKeywords, fZeroFill );

									// Load in all of the RTF control words.
	if ( storage )
	{
		_rtfHashInited = TRUE;

		for (i = 0; i < cKeywords; i++ )
		{
			HashKeyword_Insert(&rgKeyword[i]);
		}
#ifdef DEBUG						// Make sure we can fetch all these keywords.
		for (i = 0; i < cKeywords; i++ )
		{
			AssertSz ( &rgKeyword[i] == HashKeyword_Fetch ( rgKeyword[i].szKeyword ),
				"Keyword Hash is not working.");
		}
#endif
	}
}

#endif	// RTF_HASHCACHE