Comments on: Explaining GetHashCode method.

By: Diego Deberdt

Diego Deberdt — Sun, 25 Oct 2009 17:33:24 +0000

The .NET framework documentation for GetHashCode(http://msdn.microsoft.com/en-us/library/system.object.gethashcode.aspx) has some examples on how to calculate the hashcode in various classes. There does not seem to be a need to use a magic number…

By: NBA

NBA — Sat, 18 Jul 2009 21:43:43 +0000

Aside from the flawed implementation of the hashcode, the implementation of Equals is incorrect – it will throw an exception if the object being compared to is not an instance of Point. You should check for this as well, e.g.
if (ReferenceEquals(null, obj) && !(obj is Point)) return false;

By: Vlad

Vlad — Wed, 01 Jul 2009 00:11:00 +0000

This will be the best Hash for a point
((_x % Int16.MaxValue) << 16) + (_y % Int16.MaxValue)

By: abc_d

abc_d — Thu, 30 Apr 2009 14:53:35 +0000

It’s just a prime that’s big enough to overflow.

By: Vadim

Vadim — Fri, 01 Aug 2008 01:34:56 +0000

Chris,

(_x + _y).GetHashCode() is not a good algorithm for a Hash Code. If _x = 2 and _y = 3, you will get the same hash code for:

(2 + 3).GetHashCode() and (3 + 2).GetHashCode().

Unfortunately I cannot answer your question about 397. I’ve seen that people smarter than I’m were using this magical number so I shamelessly copied it.

If you or someone else will figure out the mystery behind 397, please drop me note.

By: Chris

Chris — Thu, 31 Jul 2008 21:18:43 +0000

Err, (_x.ToString() + _y.ToString()).GetHashCode()

By: Chris

Chris — Thu, 31 Jul 2008 21:17:48 +0000

How did you arrive at (x_ * 397) ^ _y for the value of Point.GetHashCode()? Why not (x_ * 396) ^ _y, for example, or (_x + _y).GetHashCode()?