ss_bmh.c

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/*
 * (c) Copyright 1992, 1993 by Panagiotis Tsirigotis
 * All rights reserved.  The file named COPYRIGHT specifies the terms 
 * and conditions for redistribution.
 */

static char RCSid[] = "$Id" ;

char *malloc() ;

#include "ss_impl.h"

PRIVATE int bmh_setup() ;
PRIVATE char *bmh_match() ;
PRIVATE void bmh_done() ;

struct ss_ops __strs_bmhops = { bmh_setup, bmh_match, bmh_done } ;


PRIVATE int bmh_setup( hp )
	header_s *hp ;
{
	register int patlen = SS_PATLEN( hp ) ;
	register int limit = patlen - 1 ;			/* patlen is > 0 */
	register char *pattern = SS_PATTERN( hp ) ;
	register int i ;
	shift_int *shift ;

	shift = (shift_int *) malloc( ALPHABET_SIZE * sizeof( shift_int ) ) ;
	if ( shift == (shift_int *)NULL )
		return( SS_ERR ) ;

	for ( i = 0 ; i < ALPHABET_SIZE ; i++ )
		shift[ i ] = patlen ;
	
	for ( i = 0 ; i < limit ; i++ )
		shift[ (unsigned char) pattern[ i ] ] = limit - i ;

	BMH_HEADER( hp )->shift = shift ;
	return( SS_OK ) ;
}


PRIVATE char *bmh_match( hp, str, len )
	header_s *hp ;
	register char *str ;
	int len ;
{
	register int i ;
	int patlen = SS_PATLEN( hp ) ;
	char *pattern = SS_PATTERN( hp ) ;
	register char lpc = pattern[ patlen-1 ] ;		/* last pattern character */
	shift_int *shift = BMH_HEADER( hp )->shift ;

	i = patlen - 1 ;
	while ( i < len )
	{
		char c = SS_MAP( hp, str[ i ] ) ;

		if ( c == lpc )
		{
			int j, k ;

			for ( j = patlen-1, k = i ;; )
			{
				if ( j == 0 )
					return( &str[ k ] ) ;
				j--, k-- ;
				if ( pattern[ j ] != SS_MAP( hp, str[ k ] ) )
					break ;
			}
		}
		i += shift[ (unsigned char) c ] ;
	}
	return( CHAR_NULL ) ;
}


PRIVATE void bmh_done( hp )
	header_s *hp ;
{
	(void) free( (char *)BMH_HEADER( hp )->shift ) ;
}