[DOC] clarify safety of integer utils

[wence-]

Describe the bug

Noticed while implementing saturating addition for rolling window work.

This is a minor thing, and I think all the usages in libcudf are safe anyway, but...

In integer_utils.hpp we have (for signed integers).

template <typename I>
constexpr I div_rounding_up_safe(std::integral_constant<bool, true>, I dividend, I divisor) noexcept
{
  auto quotient  = dividend / divisor;
  auto remainder = dividend % divisor;
  return quotient + (remainder != 0);
}

This doesn't work for divisor == 0 (OK, fine). It also overflows for divisor == -1 since INT_MIN / -1 is undefined.

I think all the usages in libcudf are for dividing two positive integers, in which case it's probably fine.

[davidwendt]

This is an internal function so there is no binding contract here and 'safe' is a relative term.
Do you have a problem with the name? I don't think it is worth renaming perhaps.
Do you wish for a safer version that checks the conditions you mentioned?
How would you like to see this issue closed?

[wence-]

How would you like to see this issue closed?

Probably just to document these edge cases.