Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

Simple md5 question - leading zeros

Posted on 2004-09-19
8
Medium Priority
?
549 Views
Last Modified: 2008-01-16
hi,

I have come across this code at many places on net

StringBuffer hexString = new StringBuffer();
for (int i=0; i < digest.length; i++) {
    String hex = Integer.toHexString(0xFF & digest[i]);
    if (hex.length() == 1) {
        hexString.append("0" + hex);
    } else {
        hexString.append(hex);
    }
}

my question is -- what's the use of doing
0xFF & digest[i]

Thnx...
0
Comment
Question by:kumvjuec
  • 4
  • 4
8 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 12096622
That would be to 'unsign' the byte value, which of course is a signed type
0
 
LVL 3

Author Comment

by:kumvjuec
ID: 12096633
thnx cehj, can u explain li'l more...

how can a byte value be signed.. and how this operation will make difference
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 12096856
It's actually not only to unsign it - it's to ensure the value does not exceed 0xFF after being passed to Integer.toHexString. Let's assume that digest[i] is itself 0xFF (-1)

Integer.toHexString(0xFF)

would produce

"ffffffff"

because of 'sign extension'. ANDing 0xFF with 0xFF would produce as a hex int

000000FF, and when that int is passed to Integer.toHexString, you'd get

"ff", which is what you want
0
What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

 
LVL 3

Author Comment

by:kumvjuec
ID: 12096928
cehj,
can u also give me a code to demonstrate this. I tried
"System.out" ing the Integer.toHexString(0xff) and Integer.toHexString(0xff & 0xff)
but both are printing out the same thing
i.e 0xff

Thanks,
0
 
LVL 3

Author Comment

by:kumvjuec
ID: 12096934
sorry, they are printing out ff instead.
0
 
LVL 86

Accepted Solution

by:
CEHJ earned 500 total points
ID: 12097008
That's because you're using an integer literal instead of a byte and those values will not be sign extended. Try this

byte b = (byte)0x80; // (-128)
System.out.println(Integer.toHexString(b));
0
 
LVL 3

Author Comment

by:kumvjuec
ID: 12097020
thnx cehj
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 12097062
8-)

Rather than calling Integer.toHexString, you may find the following more efficient:

            System.out.println(byteArrayToHexString(new byte[] { (byte)0xca, (byte)0xfe, (byte)0xba, (byte)0xbe}));

...........

            public static String byteArrayToHexString(byte[] rawBytes) {
                  String charIndex = "0123456789abcdef";
                  StringBuffer sb = new StringBuffer(rawBytes.length * 2);
                  for (int i = 0; i < rawBytes.length; i++) {
                        int ix = (rawBytes[i] >> 4) & 0xF;
                        sb.append(charIndex.charAt(ix));
                        ix = rawBytes[i] & 0xF;
                        sb.append(charIndex.charAt(ix));
                  }
                  return sb.toString();
            }
0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Java Flight Recorder and Java Mission Control together create a complete tool chain to continuously collect low level and detailed runtime information enabling after-the-fact incident analysis. Java Flight Recorder is a profiling and event collectio…
Introduction This article is the last of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers our test design approach and then goes through a simple test case example, how …
Viewers will learn about if statements in Java and their use The if statement: The condition required to create an if statement: Variations of if statements: An example using if statements:
How to fix incompatible JVM issue while installing Eclipse While installing Eclipse in windows, got one error like above and unable to proceed with the installation. This video describes how to successfully install Eclipse. How to solve incompa…
Suggested Courses

782 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question