Date: Fri, 03 Apr 2026 13:59:18 +0000
> Another thought I had when it comes to std::big_int procedurally is that we may want to walk before we run.
>
> Tiago's P3161R4 has been in the pipeline for a long time, and adds prerequisite functions such as std::mul_wide. Widening multiplication is necessary to implement multi-precision multiplication in std::big_int. Similarly, Daniel Towner provides funnel-shifting in P4010R0, which is necessary to implement multi-precision bit-shifting.
>
I'm not sure operations on std::big_int would be in scope. In the std::mul_wide case the function would need some manner of taking two arrays of limbs (since std::big_int doesn't exist), and then applying a variety of algorithms depending on the bit counts (e.g. Karatsuba, Toom-Cook, etc). P3161R4 reads to me that the goal is to provide thin wrappers around intrinsics rather than implement true arbitrary precision. Having std::add_carry would be convenient, but certainly not show stopping.
Matt
>
> Tiago's P3161R4 has been in the pipeline for a long time, and adds prerequisite functions such as std::mul_wide. Widening multiplication is necessary to implement multi-precision multiplication in std::big_int. Similarly, Daniel Towner provides funnel-shifting in P4010R0, which is necessary to implement multi-precision bit-shifting.
>
I'm not sure operations on std::big_int would be in scope. In the std::mul_wide case the function would need some manner of taking two arrays of limbs (since std::big_int doesn't exist), and then applying a variety of algorithms depending on the bit counts (e.g. Karatsuba, Toom-Cook, etc). P3161R4 reads to me that the goal is to provide thin wrappers around intrinsics rather than implement true arbitrary precision. Having std::add_carry would be convenient, but certainly not show stopping.
Matt
Received on 2026-04-03 13:59:30