Re: Fast hash of NSData?
Re: Fast hash of NSData?
- Subject: Re: Fast hash of NSData?
- From: Scott Ribe <email@hidden>
- Date: Fri, 29 Nov 2013 19:26:11 -0700
On Nov 29, 2013, at 12:58 PM, 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. It doesn’t need to be of crypto-standard, but SHA-1 was convenient. Note that this can’t be the same as simply seeing whether one object is the same as another - I really do need to know if two different objects hold the same data bytes, and to derive a short, unique value that can be used as a key.
>
> I’ve previously written my own quick-and-dirty hash that was basically a weighted sum of the bytes, modulo some number, but it turned out to have collisions more often than I expected, so SHA-1 was then used to fix that problem. Now it’s causing quite a noticeable performance hit in some cases.
I recently (last week, no kidding) investigated this question, and went with murmur hash.
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