  o RooStats::HistFactory::PiecewiseInterpolation
  o RooStats::HistFactory::PiecewiseInterpolation

    - Performance optimization: replace chained if() with a switch,
      replace .at() with [] to avoid repeated bounds-checking

    - Remove largs swaths of commented out obsolete code

    - Performance tuning of icode=4 algorithm: avoid unnecessary
      multiplications by contracting these in precalculated constants,
      calculate higher powers of x in terms of previously calculated
      powers, improve internal if() chain to converge faster
      Add comment to NOT touch this code --> this segment of code
      dominates HistFactory CPU performance in many use cases.

tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,kirbyherm/root-r-tools,kirbyherm/root-r-tools,kirbyherm/root-r-tools,tc3t/qoot,kirbyherm/root-r-tools,ffurano/root5,ffurano/root5,ffurano/root5,Dr15Jones/root,Dr15Jones/root,ffurano/root5,tc3t/qoot,Dr15Jones/root,Dr15Jones/root,Dr15Jones/root,tc3t/qoot,kirbyherm/root-r-tools,ffurano/root5,Dr15Jones/root,tc3t/qoot,ffurano/root5,tc3t/qoot,kirbyherm/root-r-tools,tc3t/qoot,ffurano/root5,kirbyherm/root-r-tools,Dr15Jones/root