==== algorithms ====
  * ''Binary GCD algorithm''
    * https://en.algorithmica.org/hpc/algorithms/gcd/
      * describes this algorithm in an easy to understand way. It first talks about the ''Euclid's algorithm'' and how ''binary GCD algorithm'' does it better.
    * https://en.wikipedia.org/wiki/Binary_GCD_algorithm
      * The algorithmica link is better than this.
    * also known as ''Stein's algorithm'' or the ''binary Euclidean algorithm''