 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Java Forum / General / February 2007Question about BigIntegers and byte[] input
I have a byte[] as an input 8B F2 99 7D 67 F1 7C 15 B2 99 2C 2E 33 DD C6 65 2D CD E7 2B and I feed it into a BigInteger so that I can do simply compares and easy formatting. However, when I call the toString(16) I get 74 0d 66 82 98 0e 83 ea 4d 66 d3 d1 cc 22 39 9a d2 32 18 d5 I am sure, in it's own way, it is "right" but I need to understand why this is occurring. Since these values represent hashes I will be for sure asked by they are the same as what was recorded for them. Christian http://christian.bongiorno.org Sideswipe wrote On 02/16/07 09:25,: > I have a byte[] as an input > [quoted text clipped - 9 lines] > this is occurring. Since these values represent hashes I will be for > sure asked by they are the same as what was recorded for them. Try making the byte[] array one position longer and inserting a zero at the beginning: 00 8B F2 99 ... If that doesn't spark the "Aha!" moment, you could (as a last resort) read the Javadoc for the BigInteger(byte[]) constructor, paying special attention to the words "two's complement."  SignatureEric.Sosman@sun.com AHA! > Sideswipe wrote On 02/16/07 09:25,: > [quoted text clipped - 24 lines] > -- > Eric.Sos...@sun.com > I have a byte[] as an input > [quoted text clipped - 12 lines] > Christian > http://christian.bongiorno.org Shouldn't there be a "-" at the start of the toString() result? A 2's complement number, represented in hex, beginning with "8" is negative. The output you got is the absolute value of the input. It's a bit easier to see, at least if you can do hex arithmetic, if you line up the input and output: 8B F2 99 7D 67 F1 7C 15 B2 99 2C 2E 33 DD C6 65 2D CD E7 2B 74 0d 66 82 98 0e 83 ea 4d 66 d3 d1 cc 22 39 9a d2 32 18 d5 Patricia > Shouldn't there be a "-" at the start of the toString() result? The value of copy and paste vs. paraphrase. - Lew My thanks to the group again. I read the part about 2's compliment but it hadn't occurred to me to simply front pad it with 00 to get what I wanted -- that makes perfect sense. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.