https://issues.dlang.org/show_bug.cgi?id=20260

          Issue ID: 20260
           Summary: CustomFloat with 0 precision/exponentWidth
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: minor
          Priority: P1
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: dlang@croco-puzzle.com

Both cases should be caught by template-constraint:

unittest
{
    auto a = CustomFloat!(0, 7)(0.0);
    auto b = CustomFloat!(7, 0)(0.0);
}

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