[jira] [Created] (CALCITE-1071) Improve hash functions

["Julian Hyde (JIRA)" <ji...@apache.org>]

Julian Hyde created CALCITE-1071:
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             Summary: Improve hash functions
                 Key: CALCITE-1071
                 URL: https://issues.apache.org/jira/browse/CALCITE-1071
             Project: Calcite
          Issue Type: Bug
            Reporter: Julian Hyde
            Assignee: Julian Hyde


There are hash functions in Utilities.hash and Util.hash and spread throughout the code, e.g. in ColumnMetaData and ClassDeclaration (search for uses of Object.hashCode).

Suggested improvements:
* Some multiply by 37; I'm not sure that all CPUs can multiply by 37 in one instruction; switch to a mersenne prime (2 ^ n - 1).
* Util.hash uses shift and xor. Change that to multiply by a prime.
* Lists should continue to multiply by 31 to be consistent with java.util.List.
* Deprecate Util.hash methods and use Utilities.hash instead.

Changing hash functions may cause some test output to change; be prepared for that.



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