working with binary or HEX data

[Bong]

I'm trying to do something I know how to do in Tcl but not, apparently in Java:

I have a binary file. It consists of sequential uniform length records (lets say 256 bytes each). I want to read 1 record, compute a checksum (by converting each byte to an integer and summing them), then write out the record and the checksum and go on to the next. I think I'm stumbling on to a signed/unsigned problem.

I open the file and read the entire contents into a Byte Array that I then convert to a String:

DataInputStream in=new DataInputStream(new FileInputStream(fin));
int nbytread=in.read(datain,0,flen);
String datast = new String(datain);

I then have a loop defining the start and stop substring addresses in the string, get the substring representing the pertinent record ...
String tstr = datast.substring(add1,add2);
and pass it to a checksum method:
int cs=compCS(tstr);

I think that's going ok. My problem seems to be inside the checksum method where I convert the string (1 character at a time) to and integer:

public static int compCS (String hstr) {
int slen = hstr.length();
int chsm = 0;
for (int i=0; i<slen; i++) {
char hc = hstr.charAt(i);
int tempint=(int)hc;
//tempint= (tempint + 0x10000 ) % 0x10000;
chsm += tempint;
System.out.print(&quot;int@char: &quot;+tempint+&quot;; &quot;
}
return chsm;
}
the converted integer gets squirrely at 127 (when the msb goes to 1). Is there a way to do this?

Bob Rashkin
rrashkin@csc.com

 

[palbano]

Don't know if this will help:

public static long checksum( String sin){

	long lret = 0;
	byte[] byt = sin.getBytes();
	for( int n=0; n<byt.length; n++)
		lret += byt[n];

	return lret;
}

-pete

 

[Bong]

Thanks. That was great. Bob Rashkin
rrashkin@csc.com

 

[Bong]

I spoke to soon. It's still treating bytes with a &quot;1&quot; in the most significant bit as negative numbers. How do I make them unsigned bytes? Bob Rashkin
rrashkin@csc.com

 

[palbano]

Bob, your right! my bad, try this:

public static long checksum( String s){
	long lret = 0;
	byte[] byt = sin.getBytes();
	for( int n=0; n<byt.length; n++)
	  lret += (long)(byt[n] & 0xff);

	return lret;
}

-pete

 

[Bong]

Thanks Bob Rashkin
rrashkin@csc.com