Re: NSMapTable with C strings as keys
Re: NSMapTable with C strings as keys
- Subject: Re: NSMapTable with C strings as keys
- From: Greg Parker <email@hidden>
- Date: Tue, 28 May 2013 15:55:48 -0700
On May 28, 2013, at 3:39 PM, Michael Hall <email@hidden> wrote:
> On May 28, 2013, at 5:27 PM, Michael Hall wrote:
>> I thought I saw SHA-1 being used as a general purpose hash function somewhere sort of surprising recently but I'm not remembering exactly where.
>
> Ah, sorry to reply to my own but maybe this was it…
>
> https://news.ycombinator.com/item?id=4036878
> SHA-1is still used in applications such as git as a general purpose hash function.
>
> Not this particular article where I saw it but I recently signed up on git and think I may of seen it's use then.
For this sort of use I expect SHA-1 is chosen in part because it computes a bigger value than a typical hash-table hash. (160 bits for SHA-1 and 256+ for SHA-2, versus 32 or 64 for a typical hash table.)
git in particular wants an ID that is as globally unique as possible so 64 bits is not enough, is computing a small number of hashes so the extra per-hash setup time for a cryptographic hash is less important, and is probably I/O bound anyway so the extra CPU time of a cryptographic hash is less important.
--
Greg Parker email@hidden Runtime Wrangler
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