[FEA]: `ceil_div` should return the resulting type of its operation

[fbusato]

Is this a duplicate?

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Area

libcu++

Is your feature request related to a problem? Please describe.

currently ceil_div(T, U) always returns the type T, which is not intuitive and bug-prone

Describe the solution you'd like

ceil_div(T, U) should instead return decltype(T{} / U{})

Describe alternatives you've considered

No response

Additional context

No response

[miscco]

I do not believe this is the correct solution.

Due to integer promotion rules this would lead to ceil_div returning int even when both arguments are short.

As always we can use common_type_t if we want to but I am not sure whether this is actually something that is desirable

[fbusato]

we use types that are at least 32-bit 99% of the cases. Smaller types are edge cases.
I don't have any issue of using common_type_t instead of decltype.

On the other hand, std defines all functions with decltype for c++14, e.g. https://en.cppreference.com/w/cpp/utility/functional/divides_void. It would also make sense to follow this.
Second, it is more efficient to return a 32-bit value than cast back and forth from a smaller type.

[fbusato]

@bernhardmgruber What is your opinion? I'm fine with any of them.

[bernhardmgruber]

I don't have a strong opinion either. @gonzalobg designed the original facility IIRC, maybe he wants to chime in.