Ruby has build-in bignumber calculator as described at:
https://sites.google.com/site/gyakuhikiruby/home/shu-zhi
I wrote Bignumber class to implement bignumbers PLUS and MULTIPLE for Ruby without using Ruby build-in bignumber.
Use naive algorithm
Use Karatsuba
algorithm from
http://www.geeksforgeeks.org/divide-and-conquer-set-2-karatsuba-algorithm-for-fast-multiplication/
cd `path-to-Bignumbercalculator`
ruby sample.rb
Optimize code