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FireSlash
 Post subject: hashCode for Vec2
PostPosted: Fri Jan 02, 2009 5:25 am 
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Joined: Sat Oct 04, 2008 3:58 am
Posts: 99
Here's a quickie you can copy/paste if you're feeling lazy :)
EDIT updated to use AndyKorth's hashCode function since mine was really really bad :D
Code:
      public boolean equals(Object obj)
      {
         if(obj instanceof Vec2)
         {
            Vec2 v = (Vec2) obj;
            if(this.x == v.x && this.y == v.y)
               return true;
         }
         return false;
      }
      @Override
      public int hashCode()
      {
         return 997 * ((int)x) ^ 991 * ((int)y); //large primes!
      }


Last edited by FireSlash on Sat Jan 03, 2009 2:14 am, edited 2 times in total.

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manunderground
 Post subject:
PostPosted: Fri Jan 02, 2009 5:40 am 
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Joined: Tue Jun 17, 2008 5:11 pm
Posts: 336
Would the hash work for the following vectors?

Code:
Vector v1 = new Vector(0, 1);
Vector v2 = new Vector(1, 0);


Or would we expect those to be identical?

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FireSlash
 Post subject:
PostPosted: Fri Jan 02, 2009 2:49 pm 
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Joined: Sat Oct 04, 2008 3:58 am
Posts: 99
manunderground wrote:
Would the hash work for the following vectors?

Code:
Vector v1 = new Vector(0, 1);
Vector v2 = new Vector(1, 0);


Or would we expect those to be identical?

Yeah, I never said it was a good hashing function :wink:
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AndyKorth
 Post subject:
PostPosted: Fri Jan 02, 2009 10:18 pm 
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Joined: Thu Nov 20, 2008 5:16 am
Posts: 76
Code:
    @Override
    public int hashCode() {
        return 997 * x ^ 991 * y; //large primes!
    }
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FireSlash
 Post subject:
PostPosted: Sat Jan 03, 2009 2:12 am 
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Joined: Sat Oct 04, 2008 3:58 am
Posts: 99
AndyKorth wrote:
Code:
    @Override
    public int hashCode() {
        return 997 * x ^ 991 * y; //large primes!
    }

Edited my post with your function, but I had to cast x and y as ints though, which will provide some accuracy issues for people hashing against close points.
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AndyKorth
 Post subject:
PostPosted: Sat Jan 03, 2009 2:20 am 
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Joined: Thu Nov 20, 2008 5:16 am
Posts: 76
Oh... Yeah, that was from a tile based game, so everything was on a tile.
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kevglass
 Post subject:
PostPosted: Wed Jan 14, 2009 11:10 pm 
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Joined: Thu Jan 01, 1970 12:00 am
Posts: 3143
Where's Vec2 ?

I've updated Vector2f's hashCode() for the large primes though.

Kev
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FireSlash
 Post subject:
PostPosted: Sat Jan 17, 2009 12:40 am 
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Joined: Sat Oct 04, 2008 3:58 am
Posts: 99
Haha, Vec2 is part of jbox2d.. :shock:

See kids? THIS is what happens when you start mixing libs together. :cry:
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