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Quick and Simple Hash Code Combinations

Asked 2009-10-29T21:53:21.353
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Can people recommend quick and simple ways to combine the hash codes of two objects. I am not too worried about collisions since I have a Hash Table which will handle that efficiently I just want something that generates a code quickly as possible.

Reading around SO and the web there seem to be a few main candidates:

  1. XORing
  2. XORing with Prime Multiplication
  3. Simple numeric operations like multiplication/division (with overflow checking or wrapping around)
  4. Building a String and then using the String classes Hash Code method

What would people recommend and why?

c# algorithm hash hashcode
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1 Answer

-1

If your input hashes are the same size, evenly distributed and not related to each other then an XOR should be OK. Plus it's fast.

The situation I'm suggesting this for is where you want to do

H = hash(A) ^ hash(B); // A and B are different types, so there's no way A == B.

of course, if A and B can be expected to hash to the same value with a reasonable (non-negligible) probability, then you should not use XOR in this way.

answered 2009-10-29T21:57:11.033

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