Re: Hash support for arrays - Mailing list pgsql-hackers

From marcin mank
Subject Re: Hash support for arrays
Date
Msg-id AANLkTindyRFhaB-dbtFHhbBst8c+U9Gd0Q0rbLZao4MZ@mail.gmail.com
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In response to Hash support for arrays  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Hash support for arrays
List pgsql-hackers
On Sat, Oct 30, 2010 at 6:21 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> 3. To hash, apply the element type's hash function to each array
> element.  Combine these values by rotating the accumulator left
> one bit at each step and xor'ing in the next element's hash value.
>
> Thoughts?  In particular, is anyone aware of a better method
> for combining the element hash values?
>

This would make the hash the same for arrays with elements 32 apart swapped.

This is what boost does:
http://www.systomath.com/include/Boost-1_34/doc/html/boost/hash_combine.html

Greetings


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