google / cityhash

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CityHash128 isn't thorough enough

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What steps will reproduce the problem?
1. CityHash128() all 144-byte strings with 3 bits set
2. check for collisions

What is the expected output? What do you see instead?

0 collisions are expected.  87 collisions are actually seen.  I saw the first 
collision after about 8 million of the keys.  That's the expected collision 
rate for a 46-bit hash, not a 128-bit hash.

(I had a hash of my own last year, AkronHash, that was also a 128-bit hash 
evolved from MurmurHash.  I quickly withdrew it due to similar quality issues.  
My current attempt, SpookyHash, passes this test.)


Original issue reported on code.google.com by bobjenki...@gmail.com on 28 Jul 2011 at 8:00

Thanks Bob!

We will fix this in a future release.

Original comment by gp...@google.com on 31 Aug 2011 at 8:43

  • Changed state: Started
  • Added labels: Priority-High
  • Removed labels: Priority-Medium
Fixed in version 1.0.3.  Thanks again for the bug report!

Original comment by gp...@google.com on 6 Oct 2011 at 9:05

  • Changed state: Fixed