This sass extension utilises the Greated Common Divisor (gcd) algorithm to reduce duplicate styles, especially when making your own grid system.

gcd_sass_extension.rb

#!/usr/bin/env ruby

# To implement extension, run this command in a shell:
#   $ sass -i -r ./gcd_sass_extension.rb
# Or require it in compass config
#   require './gcd_sass_extension'
module Sass::Script::Functions

  # 
  # Uses the 'greatest common divisor' algorithm to work out if a fraction
  # (represented by the method arguments) can be simplified further. Which is 
  # useful for batch generation of unique fractions without duplicates (.e.g
  # 1/2 and 2/4, etc.), such as grid system class names.
  # 
  # @param num_1 [Integer] The numerator of the fraction
  # @param num_1 [Integer] The denominator of the fraction
  # 
  # @return [Integer] The greatest common divisor, divide both numerator
  #                   and denominator by this to find the simplified fraction
  def gcd num_1, num_2
    num_1 = num_1.value if num_1.respond_to?(:value)
    num_2 = num_2.value if num_2.respond_to?(:value)

    if num_2 == 0
      Sass::Script::Number.new num_1
    else
      gcd num_2, num_1%num_2
    end
  end
  declare :gcd, :args => [:number, :number]

end