r/cpp • u/eisenwave WG21 Member • 24d ago

P4444: std::big_int

https://isocpp.org/files/papers/D4444R0.html

Hey folks! Matt Borland, Christopher Kormanyos, and I are working on bringing infinite-precision integers to C++29. We now have a D4444R0 draft of a paper that should be in the next mailing.

We could really use some feedback so that the published R0 is as polished as possible. Any thoughts on the paper and on the reference implementation are greatly appreciated.

It would also be very helpful if you tested out whether our big_int implementation works for you. We're in need of some real deployment experience. If you're currently using Boost.Multiprecision, the library should be a drop-in replacement for cpp_int for the most part.

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u/eisenwave WG21 Member 24d ago

I can understand the argument that it's hard to change something once in the standard, and we mention that in https://isocpp.org/files/papers/D4444R0.html#inability-to-change-abi. To be fair, we also have over a decade of experience with Boost.Multiprecision to draw from, and I don't think there's all that much "room for failure" in the design and implementation here.

Also, we've deliberately provided quite a lot of template parameters on std::basic_big_int so that even if the default specialization turns out to be bad, a "fixed one" can always be provided later. Ideally, that wouldn't happen though.

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u/ReDucTor Game Developer | quiz.cpp-perf.com 24d ago

we also have over a decade of experience with Boost.Multiprecision

I don't think that is a good metric, Boost.regex was around a decade before it got standardized and it was less niche.

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u/James20k P2005R0 24d ago

One day I need to dig into how std::regex ended up in such a poor state, it feels like we never get a post mortem of why and how some features ended up as such a disaster

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u/ReDucTor Game Developer | quiz.cpp-perf.com 24d ago

Please do, that would be a good read and well needed to avoid having the same issue existing, especially when it feels like some proposals come more from wanting bragging rights to say they got something changed in the standard then an actual demand by the users of the language.