countsetbits problem with lookup table approach, runs in O(1) time

[ggorantala]

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• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.75%. Comparing base (1feceb7) to head (8b19b28).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5573      +/-   ##
============================================
+ Coverage     54.73%   54.75%   +0.01%     
- Complexity     3451     3454       +3     
============================================
  Files           538      538              
  Lines         15574    15583       +9     
  Branches       2959     2961       +2     
============================================
+ Hits           8525     8532       +7     
- Misses         6693     6694       +1     
- Partials        356      357       +1     

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[siriak]

Looks good, thanks!