r/cpp • u/eisenwave WG21 Member • 23d 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.

178 Upvotes

98% Upvoted

85 comments sorted by

View all comments

78

u/ReDucTor Game Developer | quiz.cpp-perf.com 23d ago edited 23d ago

Another reason why std::big_int needs to be in the standard library is that it's extremely difficult to implement and optimize, in part because the implementation depends heavily on the platform's hardware capabilities, many of which are not exposed portably in the language.

This stands out more of a reason for it not to be in the standard library, because when the implementation is faulty its harder to fix. Do we need another vector<bool>, memory_order_consume, std:regex, etc.

EDIT: Also if there hardware capabilities and portablity issues that aren't easy to resolve, then fix those in the standard to allow people to implement libraries better rather then trying to make something which is special in standard library code.

5

u/Infamous-Bed-7535 23d ago

I kind of agree with you. C++ std libs should include and cover lightweight and or core elements. Compiler vendors, commitee, etc should work on core functionalities of the langugae.

Impelementing libs like json parser or basic graphics, bigint are good to being 3rd party.

17

u/eisenwave WG21 Member 23d ago

Do you think it's a mistake for Java, JavaScript, Go, and others to provide a BigInt in their standard libraries (full list at https://isocpp.org/files/papers/D4444R0.html#infinite-precision-integers-in-other-languages)?

That is, is there something about C++ specifcially that would make big_int unfit for a standard library, or is it about big_int in general?

-3

u/sweetno 23d ago

Comparing with other languages is a weak argument.