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Path: utzoo!linus!decvax!decwrl!pyramid!amiga!neil
From: neil@amiga.UUCP (Neil Katin)
Newsgroups: net.micro.amiga
Subject: Dos hash function
Message-ID: <987@amiga.amiga.UUCP>
Date: Sat, 12-Apr-86 03:56:54 EST
Article-I.D.: amiga.987
Posted: Sat Apr 12 03:56:54 1986
Date-Received: Mon, 14-Apr-86 00:43:47 EST
Reply-To: neil@rocky.UUCP (Neil Katin)
Organization: Commodore-Amiga Inc., 983 University Ave #D, Los Gatos CA 95030
Lines: 46


Recently several people have asked for the dos directory hash function.
Here is a small program that computes it.  The hash value is the longword
offset into the directory block, NOT into the hash table (I just love that
BCPL...).

Anyway, hope it helps.

	Neil Katin
	Commodore-Amiga Inc.
	pyramid!amiga!neil

---- cut here --------------------
main( argc, argv )
int argc;
char **argv;
{
    if( argc != 2 ) {
        printf( "Usage: %s <name>\n", argv[0] );
        exit( 1 );
    }

    printf( "hash is %ld\n", (hash( argv[1] ) % 72) + 6 );

}
 
hash( s )
unsigned char *s;
{
    int i;
    int res;
    unsigned char *sp;
    unsigned c;

    res = strlen( s );

    for( i = 1, sp = s; *sp; i++, sp++ ) {
        c = *sp;
        if( c >= 'a' && c <= 'z' ) {
            c = c - 'a' + 'A';
        }
        res = ((res * 13 + c ) & 0x7ff);
    }
    return( res );
}