References
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   * Donald E. Knuth, "The Art of Computer Programming", vol 2,
     "Seminumerical Algorithms", 2nd edition, Addison-Wesley, 1981.

   * John D. Lipson, "Elements of Algebra and Algebraic Computing", The
     Benjamin Cummings Publishing Company Inc, 1981.

   * Richard M. Stallman, "Using and Porting GCC", Free Software
     Foundation, 1995.

   * Peter L. Montgomery, "Modular Multiplication Without Trial
     Division", in Mathematics of Computation, volume 44, number 170,
     April 1985.

   * Torbjorn Granlund and Peter L. Montgomery, "Division by Invariant
     Integers using Multiplication", in Proceedings of the SIGPLAN
     PLDI'94 Conference, June 1994.

   * Tudor Jebelean, "An algorithm for exact division", Journal of
     Symbolic Computation, v. 15, 1993, pp. 169-180.

   * Kenneth Weber, "The accelerated integer GCD algorithm", ACM
     Transactions on Mathematical Software, v. 21 (March), 1995, pp.
     111-122.