Unsigned division in Java

iago · November 21, 2003, 12:05 PM

After much pondering, I figured it out. It's a little messy, but isn't all that bad:

        public static int Divide(int a, int b)
        {
                long c = a;
                long d = b;

                c = c & 0xFFFFFFFFl;
                d = d & 0xFFFFFFFFl;

                long lResult = (long)c / (long)d;                               

                return (int)(lResult & 0xFFFFFFFFl);
        }

Which can be shortened to this:

Code Select

        public static int Divide(int a, int b)
        {                                                                       
                // Basically, we treat them as longs then mask out the sign-    
                // extension.                                                   
                return (int)(((long) a & 0xFFFFFFFFl) / ((long) b & 0xFFFFFFFFl));                                                                               
        }

[edit] Fixed a line break that vi added
[edit2] Fixed a small glitch with the second program

Banana fanna fo fanna · November 21, 2003, 02:17 PM

+a million

iago · November 21, 2003, 02:19 PM

I'm wondering what kp will say, mostly

Kp · November 21, 2003, 02:31 PM

Quote from: iago on November 21, 2003, 02:19 PM
I'm wondering what kp will say, mostly

If you wanted unsigned division, why are you using Java?

iago · November 21, 2003, 04:39 PM

Quote from: Kp on November 21, 2003, 02:31 PM
Quote from: iago on November 21, 2003, 02:19 PM
I'm wondering what kp will say, mostly

If you wanted unsigned division, why are you using Java?

I did it in a fairly clean way, though!

Adron · November 21, 2003, 08:23 PM

I noted before that you can do unsigned multiply and divide by using signed numbers with > twice the bits.

iago · November 21, 2003, 09:32 PM

I don't remember you noting that, but it's fairly logical if you think about it.

Adron · November 21, 2003, 09:44 PM

Yes. What you have to be careful about is that you need 64-bit signed numbers to handle 16-bit unsigned, unless there's some trick I missed.