An implementation of Integer square root (needed when working with very large numbers).

integer-sqrt.rb

# Copyright (c) 2014 Justin W. Smith <justin.w.smith@gmail.com>
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class Integer
  def isqrt
    return 0 if zero?
    return 1 if self == 1
    return nil if self < 0
    x_k = next_x_k = (self >> 1)
    begin
      x_k = next_x_k
      next_x_k = (x_k + self/x_k) >> 1
    end until (x_k - next_x_k) <= 0
    return x_k
  end
end