| From: | Erik Jones <ejones(at)engineyard(dot)com> |
|---|---|
| To: | Craig Ringer <craig(at)postnewspapers(dot)com(dot)au> |
| Cc: | Bill Moran <wmoran(at)potentialtech(dot)com>, Jasen Betts <jasen(at)xnet(dot)co(dot)nz>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Re: Mapping output from a SEQUENCE into something non-repeating/colliding but random-looking? |
| Date: | 2009-05-03 01:07:08 |
| Message-ID: | AB5B0C2A-4A20-48B8-9054-656878CB6E43@engineyard.com |
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| Lists: | pgsql-general |
On May 1, 2009, at 6:06 AM, Craig Ringer wrote:
<snip>
> What I'm looking for is a function that, given an input within a
> constrained range (say, a 32 bit integer) produces a different output
> within the same range. For any given input, the output should be the
> same each time, and for any given output there should only be one
> input
> that results in that output.
I think you drop the idea of a repeatable mapping you may have some
success with the Knuth (aka Fisher-Yates) shuffle algorithm: http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
Why does anything need to be repeatable when you only need to make
sure that each number is only generated once?
Erik Jones, Database Administrator
Engine Yard
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