C++ Logo


Advanced search

Re: [std-proposals] Integer overflow arithmetic

From: Jonathan Wakely <cxx_at_[hidden]>
Date: Sat, 17 Feb 2024 14:24:27 +0000
On Sat, 17 Feb 2024 at 13:49, Jan Schultke via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> Please add a rem_wide function to your proposal.
> Double-wide remainders are important for safe modular arithmetic. For
> example, std::linear_congruential_generator is commonly implemented
> using double-wide arithmetic through __int128. However, it would be
> desirable to have a general solution for any integer type.
> Your div_wide function does not cover this use case because it has the
> precondition is_div_wide_defined. A rem_wide function would have a
> wider contract. Only division by zero and the edge case of HUGE / -1
> are problematic, but the remainder always fits into a 64-bit number.

FWIW, for std::linear_congruential_generator the integers involved are
unsigned and the remainder is a compile-time constant that can't be zero,
so neither of those cases is a problem. That doesn't mean it couldn't be
useful in other situations, but isn't needed for

Received on 2024-02-17 14:25:43