Re: Fast hash of NSData?
Re: Fast hash of NSData?
- Subject: Re: Fast hash of NSData?
- From: Graham Cox <email@hidden>
- Date: Sun, 01 Dec 2013 21:31:55 +0100
On 1 Dec 2013, at 7:43 pm, Quincey Morris <email@hidden> wrote:
> I doubt I can talk you out of it, but the truth is that you — like every one of the rest of us, because we’ve got human brains — are really, really lousy at intuiting about randomness and probabilities. What we *think* isn’t worth the paper our emails are printed on.
You can talk me out of it by providing a compelling argument :)
I agree that intuition about probability is often wrong - it’s something I’m trying to gently teach my daughter right now (she’s 7). But that’s also why I stopped thinking about it and decided to measure it - I don’t have the knowledge to analyse it mathematically, so I did what I could - throw all my files at it and count the collisions. The answer was 0. That doesn’t mean it’s impossible, but it surely indicates that it’s vanishingly improbable? Our users won’t be throwing their entire hard disks at our app, they might drag in a handful of files at most.
The point of this was to improve performance. It’s not premature optimisation, we’re on our ninth major release, and performance has not so far been a major focus, but some users are pushing the limits and we need to do something for them - I mentioned one particular user file that has come down from 11 minutes to 2 seconds to import, mostly because of considering questions such as these. Besides, it makes for an interesting exchange of ideas, I think.
—Graham
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