3 ms·

Can many hashes be combined quickly in a uniform way? This is another benefit of `<`, it composes.

• masklinn 4y ago
  > Can many hashes be combined quickly in a uniform way? The XOR operator?
  • sicp-enjoyer 4y ago
    If you do that 10 times for all members of your struct, do you get good uniformly distributed keys? This post doesn't think so: https://stackoverflow.com/questions/5889238/why-is-xor-the-default-way-to-combine-hashes https://stackoverflow.com/questions/5889238/why-is-xor-the-d...
    • int_19h 4y ago
      XOR is a bad way to do it, but there are ones that work much better that are described in answers to that post, and it's what other languages use in similar situations (e.g. tuples in Python and C#): https://github.com/python/cpython/blob/71db5dbcd714b2e1297c43538188dd69715feb9a/Objects/tupleobject.c#L318-L342 https://github.com/python/cpython/blob/71db5dbcd714b2e1297c4...
      • sicp-enjoyer 4y ago
        Yes, and eventually you start computing another hash of the buffer of the concatenated members. I'm not saying it can't be done, I'm just comparing it with recursive memberwise comparison.
  • gpderetta 4y ago
    All pairs of {x,y} with x==y or hash(x)==hash(y) would hash to the same value (0). That's seems suboptimal.