Re: [hash2] Question about cryptographic guarantees of hash_append_unordered_range

From: Peter Dimov (pdimov_at_[hidden])
Date: 2024-12-08 20:32:46

Ion Gaztañaga wrote:
> El 08/12/2024 a las 21:04, Ion Gaztañaga via Boost escribió:
> > El 08/12/2024 a las 20:49, Vinnie Falco via Boost escribió:
> >> On Sun, Dec 8, 2024 at 11:44 AM Peter Dimov via Boost
> >> <boost_at_[hidden]>
> >> wrote:
> >>
> >>> Matt Borland is considering proposing boost::uint128_t to Core, but
> >>> that would mean depending on Core.
> >>>
> >>
> >> Would it be better to make this its own library? More fine-grained
> >> libraries could have appeal to Boost users.
> >
> > I wouldn't like to add another dependency to the library users.
> >
> > Wouldn't be acceptable to take all the bits from the hash, treat the
> > hash as an array 64 bit or 32 bits hashes and apply something like
> > hash_combine or similar to each element so that we combine big hashes
> > preserving all bits from result_type?
> >
> > This would also scale to 512 bit or bigger hashes.
> 
> Auto-replying...
> 
> Just realized that the operation must be commutative so hash_combine would
> not work. Maybe just adding those individual hashes could do the trick.

I suppose I can just add the individual uint64_t[] values without carry, instead of
emulating a full-featured uint128_t or uint256_t.