Editing WoW:StringHash/Analysis (section)

== Bit distribution test ==
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This test measures how many times each bit is 1 for a given set of inputs. The target value is for each bit to be 1 50% of the time, and 0 50% of the time, though there will obviously be deviations from this, which are expected and accepted, up to a certain point.

In this test, we feed each hash the same set of inputs: 10000 random strings consisting of "aaaaaaaaa" followed by 15 random bytes.

The results show the absolute difference between 50% and the result, i.e. 49.4 and 50.6 will both be reported as "0.6". Only differences of 0.5% or greater are shown (0.5% is in no way a ceiling of the expected difference; it just cuts down on the amount of output).


=== Inputs 0-255 ===
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{|
|-
||Java||StringHash 
|- valign=top
|
   2: 0.8%
   4: 0.6%
   9: 0.6%
  11: 0.5%
  13: 0.5%
  14: 0.5%
  15: 1.0%
  17: 1.1%
  20: 0.5%
  21: 0.9%
  23: 0.8%
  25: 0.9%
  28: 0.6%
  31: 0.7%
  32: 1.2%
|
   2: 0.5%
   3: 0.5%
   7: 0.7%
  12: 0.6%
  15: 0.9%
  16: 1.0%
  17: 0.9%
  20: 0.7%
  21: 1.1%
  25: 0.6%
  29: 0.8%
  30: 0.6%
  31: 0.7%
|}


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=== Inputs 32-127 ===
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{|
|- 
||Java||StringHash
|- valign=top
|
   2: 0.9%
   7: 0.7%
   8: 0.6%
   9: 0.7%
  10: 0.6%
  11: 0.6%
  12: 1.5%
  15: 0.8%
  16: 0.5%
  18: 0.7%
  22: 0.8%
  27: 0.5%
  29: 0.5%
  30: 0.6%
  32: 0.5%
|
   1: 1.0%
   3: 0.5%
   6: 0.8%
  14: 0.6%
  19: 0.5%
  23: 0.5%
  25: 0.7%
  28: 0.5%
|}


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=== Result analysis ===
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Both algorithms perform roughly as expected. With these samples, StringHash performs a little bit better, but that is to be expected as it mixes more bits; either way, the differences are not really meaningful. The test only attempts to evaluate if all possible result bits are used efficiently without unexpected "holes" in the output.

A more thorough test would attempt to find biases in different sets of bits, but that is really more meaningful for [[wikipedia:PRNG|PRNG]] testing and [[wikipedia:cryptographic hash function|secure hashes]] than it is for this type of light string hash.


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