Re: Optimization techniques, C++ numeric representations

On 27/04/2019 23:01, Hans Aberg wrote:
> On 2019-04-25 17:46, Martin Ward wrote:
>> If signed overflow was given a defined
>> behaviour (such as the two's complement result), then compilers for
>> CPUs which do not implement two's complement operations would have to
>> generate less efficient code (but does anyone still make such a CPU?).
>
> All C++ compilers use two's complement, and as of C++20, that is
> required, cf. [1], "Range of values". It is required for int32_t etc in
> C++11 [2] and C99 [3].
>
> 1. https://en.cppreference.com/w/cpp/language/types
> 2. https://en.cppreference.com/w/cpp/types/integer
> 3. https://en.cppreference.com/w/c/types/integer
> [I realize that if you look very hard, you can still find a few legacy
> machines that are not pure two's complement and do not have 8-bit byte
> addressing.  But these days, so what. -John]


Note, however, that this applies only to the representation of the
types. C++20 will /not/ require two's complement wrapping on signed
integer overflow - this will remain undefined behaviour. (And, as
always, compilers are free to define it if they want.)

Return to the comp.compilers page.
Search the comp.compilers archives again.