Re: Formal review request for Hash2

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2024-12-05 22:08:23

On 12/6/24 00:59, Ivan Matek wrote:
> 
> 
> On Thu, Dec 5, 2024 at 10:53 PM Andrey Semashev via Boost
> <boost_at_[hidden] <mailto:boost_at_[hidden]>> wrote:
> 
>     Technically, it doesn't need to be size to separate the two fields. You
>     can use any kind of separator, including a fixed one (i.e. not depending
>     on either of the fields it separates). I.e. instead of this:
> 
>     Â  "ab" | 2 | "c" | 1
> 
>     you could have this:
> 
>     Â  "ab" | separator_t{} | "c" | separator_t{}
> 
>     An empty sequence could simply be hashed as separator_t{}.
> 
>     The question is how separator_t would hash and whether it could be made
>     any faster than just hashing the size. I suppose, it could be smaller
>     (e.g. 1 byte of data instead of sizeof(size_t)), but I'm not sure if
>     that would mean anything in terms of performance.
> 
> As far as I understand that will not work. Assume separator is char 'x'Â 
> although it does not really matter what the value is, it is just for
> ease of writing. 
> 
> now 
> "a" | "xc"
> hashes same 
> as 
> "ax" | "c"
> because both produce axxc

Yes, you're right.