remove undefined bahavior

[phlptp]

change the checked_multiply function to not use undefined behavior to check for potential undefined behavior and wrapping.

See Issue #289

[codecov]

Codecov Report

Merging #290 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #290   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     12           
  Lines        2887   2894    +7     
=====================================
+ Hits         2887   2894    +7

Impacted Files	Coverage Δ
include/CLI/Validators.hpp	100% <100%> (ø)	⬆️

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[himikof]

I would like to point out that while the intent of this change is correct, the implementation fails in an edge case:

assert(checked_multiply(2, std::numeric_limits<int>::min() / 2));

I would suggest the following change, which should work for both signed and unsigned types (the second branch is never called for them):

    if (a > 0 == b > 0) {
        if ((std::numeric_limits<T>::max)() / absval(a) < absval(b))
          return false;
    }
    else {
        if ((std::numeric_limits<T>::min)() / absval(a) > -absval(b))
            return false;
    }

[henryiii]

@phlptp, will you add the test and fix from @himikof, or should I?

[phlptp]

I won't be able to get to it until tomorrow morning, if you want to wait I can do it then, otherwise go ahead. My one concern was the possibility of unused code warnings for the unsigned types.

[henryiii]

That's sooner than I could do it; I'm edging out a little time during the CoDaS-HEP workshop to catch up a little. Won't start having larger chunks of time till next week or so.

[phlptp]

I think this is ready to go now. with the additions recommended by @himikof