Re: Fast hash of NSData?
Re: Fast hash of NSData?
- Subject: Re: Fast hash of NSData?
- From: Kyle Sluder <email@hidden>
- Date: Fri, 29 Nov 2013 12:36:30 -0800
> On Nov 29, 2013, at 11:58 AM, Graham Cox <email@hidden> wrote:
>
> Another general question.
>
> Does anyone have a quick-and-dirty (but functional) way to hash NSData? I’m currently using SHA-1 but it’s quite slow. All I need is a way to determine whether one block of data is identical to another or not - but every bit counts.
Just for the sake of the list, though I'm certain you're aware of this yourself: you can't use a hash function to check for equality unless it is a perfect hash function. You can use it to reduce the number of comparisons per candidate, but you'll always wind up doing at least O(M+N) comparisons (where M is the size of your input and N is the length of your hash output).
Often, it's better to improve the data structure before trying a different hash function. It's much easier to reason about how to improve a solution in terms of algorithm analysis of your data structure rather than it is to perform an empirical analysis of a specific hash function's collision-to-speed tradeoffs.
Long way of saying: what's the actual problem you're trying to solve? Maybe a hash table is a poor fit.
--Kyle Sluder
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