RFR: 8314258: checked_cast doesn't properly check some cases [v2]

[Stefan Karlsson]

On Mon, 9 Feb 2026 21:27:18 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Please review this addition of the `integer_cast` utility.
>> 
>> Details in first comment, to avoid email spamming from automatic messages.
>> 
>> Testing: mach5 tier1-5 with `checked_cast` for integral types changed to call
>> the new `integer_cast`.  Addition of `integer_cast` includes gtests.
>
> Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:
> 
>   more testing

I've reviewed the integerCast code but not the tests. I'm having a hard time parsing this code:

    // signed => signed.  Range check with one comparison.
    using U = std::make_unsigned_t<From>;
    U ufrom = static_cast<U>(from);
    constexpr U umin = static_cast<U>(std::numeric_limits<To>::min());
    constexpr U umax = static_cast<U>(std::numeric_limits<To>::max());
    // The "usual" single-compare range check formulation would be
    //   (U)(from - min) <= (U)(max - min)
    // but that has UB overflows (both actual and potential).
    // Converting to U earlier is equivalent but avoids UB overflows.
    return (ufrom - umin) <= (umax - umin);

Is it important to have "Range check with one comparison" or could two comparisons make for clearer code? Could the compiler optimize two comparisons into one?

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PR Review: https://git.openjdk.org/jdk/pull/29582#pullrequestreview-3796733467