[CALCITE-1071] Improve hash functions

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.7.0
• Assignee: Julian Hyde
• Reporter: Julian Hyde
• Created: 29/Jan/16 20:25
• Updated: 22/Mar/16 01:18
• Resolved: 03/Feb/16 05:10

Description

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.