Read documentation for 20 minutes so apologies in advance is some of questions are too obvious. 1) did you consider using something like std::span here? I presume answer is yes, but you do not want to limit library to C++20 onwards. HashAlgorithm( unsigned char const* seed, std::size_t n ); void update( void const* data, std::size_t n ); 2) From what I see there is no way for algorithm to say it only works on aligned data, e.g. to avoid runtime check of data alignment because SIMD instructions? E.g void update_aligned<32>( void const* data, std::size_t n ); Would this be too much complication for too little performance gain(not to mention UB risk)? Not an expert, just know performance was motivation for std::assume_aligned <https://open-std.org/JTC1/SC22/WG21/docs/papers/2018/p1007r1.pdf> 3) I see there is nice trait is_contiguously_hashable trait(padding was one of first things I wondered when reading docs), and also a documentation on how to deal with other types, including when user provides his own hash customization. One thing I would ask regarding design is the following example: std::string a; int b; // not part of the salient state void const* c; friend bool operator==( X const& x1, X const& x2 ) { return x1.a == x2.a && x1.b == x2.b; } template<class Hash, class Flavor> friend void tag_invoke( boost::hash2::hash_append_tag const&, Hash& h, Flavor const& f, X const& v ) { boost::hash2::hash_append(h, f, v.a); boost::hash2::hash_append(h, f, v.b ); } Here both tag_invoke and operator == need to remember to use same fields. Would it be possible to have support so that both hash and operator == can use member function helper that returns tuple of references( to salient fields)? e.g. assume this is my current code and I want to add hash support for it. struct X { int a; short b; short cached_something; constexpr auto repr() const { return std::tie(a,b); } constexpr bool operator == (const X& other) const { return repr() == other.repr(); } }; I know Mp11 has tuple_for_each, but I wonder if it would be nice to have something that makes this idiom easier to use? 4) Paper mentioned is quite old, but if you remember... do you have some feedback paper received at the time? On Mon, Dec 2, 2024 at 8:49 PM Peter Dimov via Boost <boost@lists.boost.org> wrote:
I'd like to request a formal review for the Hash2 library
https://github.com/pdimov/hash2 https://pdimov.github.io/hash2/
(by Christian Mazakas and myself.)
The library implements an extensible framework for implementing hashing algorithms that can support user-defined types. Its structure is largely based on the paper "Types don’t know #" by Howard Hinnant, Vinnie Falco and John Bytheway.
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3980.html
We're looking for a review manager.
Comments and questions are welcome; you don't need to wait for the review.
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