Dart should provide a way of combining hashes

[blois]

Basically if one overloads operator == they should also overload hashCode and generate a 'good' hash, but Dart doesn't offer any utilities to do so. This means that many users will generate hashes with poor distributions.

The JS string class internally uses http://en.wikipedia.org/wiki/Jenkins_hash_function, it would be great if there were a public API for this.

[lrhn]

Removed Type-Defect label.
Added Type-Enhancement label.

[lrhn]

How about something like:

class JenkinsHasher {
  int _hash = 0;

  void add(int value) {
    _hash += value;
    _hash += _hash << 10;
    _hash ^= _hash >> 6;
  }
  int get hash {
    int hash = _hash;
    hash += (hash << 3);
    hash ^= (hash >> 11);
    hash += (hash << 15);
    return hash;
  }
}

Then you can use it as:
  var hash = (new JenkinsHash()..add(foo.hashCode)..add(bar.hashCode)).hash;

?

[blois]

That looks decent.

We currently have something close to this at:
https://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/sdk/lib/html/html_common/jenkins_smi_hash.dart

My understanding is that the masking in the above is needed for performance.

---

cc @rakudrama.

[jmesserly]

for the curious, the jenkins_smi_hash moved and is now at sdk/lib/math. Still private though.

[DartBot]

This comment was originally written by @chalin

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Any progress on this? I agree with blois's original concern, and the comment in the source file

class _JenkinsSmiHash {
// TODO(11617): This class should be optimized and standardized elsewhere.

[DartBot]

This comment was originally written by davidm...@google.com

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FYI it's now part of Quiver:

https://github.com/google/quiver-dart/blob/master/lib/src/core/hash.dart

[DartBot]

This comment was originally written by @chalin

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Nice. Then maybe this issue should be closed?

[blois]

We have to have this code in dart: libraries for other uses, requiring that a package version be used just adds additional app bloat. Would prefer to keep this issue open, though the presence of Quiver probably lessens the criticality of it.

[jmesserly]

+1, we can't (currently) use quiver even in many of our packages (the ones in SVN)

[stereotype441]

@floitschG Thanks--I failed to notice the duplicate issue when I filed #25553.

Given that this issue is "priority-unassigned" and has been open for 2.5 years, what is the likelihood of it getting addressed soon? As I noted in #25553, an upcoming IntelliJ feature would benefit from it, so it would be nice if we could get to it soon.

It seems like it would be a pretty simple matter of renaming a class and adding some documentation. Would it be helpful if I submitted a CL for review?