Array hashing is in Ruby 1.8 mode

[kml]

Different arrays, are hashing very similarly

>> [].hash
=> 0
>> [2].hash
=> 0

MRI's behaviour is different:

>> [].hash
=> 3252255281033687896
>> [2].hash
=> 3208161167426848866

[headius]

We calculate based on array length and hash of the elements, with some bitshifting etc.

Based on MRI's implementation it appears we're missing a few things:

• Murmur calculation of the hash
• Pseudo-random salt (MRI uses rb_ary_hash pointer address)

[Who828]

I can take this up tonight, looks like a nice bug get started.

[Who828]

Here is the change, https://gist.github.com/Who828/056848941c6efee4044e
Let me know if that's what you expected before I send the PR.

[headius]

The PR looks good, but I wonder if we should also add some kind of pseudo-random salt like MRI. Could be a one-shot random number from almost anywhere. Or we could skip it.

@enebo, @tduehr: Yay or nay? Do we need it?

[tduehr]

I think it's a good idea to have one per runtime. I'm not entirely sure the full impact, there may be some issues relating to shared objects between runtimes.

[headius]

#2443 gets us using proper hashing algorithm but does not include salting. I'll file a separate issue for that, since I think we need a bit more discussion about what to use for salt.