crypto_math.rb

module CryptoMath
  refine Fixnum do
    def factorial
      (1..self).reduce(:*) || 1
    end
  end

  refine String do
    def binary_op(other)
      throw :mismatchedStringLengths unless self.length == other.length
      other_a = other.unpack("U*")
      self.unpack("U*").map.with_index do |s, i|
        yield s, other_a[i]
      end.pack("U*")
    end

    def ^(other)
      binary_op(other) {|a, b| a^b}
    end

    def &(other)
      binary_op(other) {|a, b| a&b}
    end

    def |(other)
      binary_op(other) {|a, b| a|b}
    end

    # Returns string as an array of ascii numbers in binary
    def to_bi_a
      self.chars.map {|c| c.ord.to_s(2)}
    end

    # copied from: https://github.com/emonti/rbkb/blob/a6d35c0fd785bae135034502b1d07ed626aebde5/lib/rbkb/extends/string.rb#L163
    def entropy
      e = 0
      sz = self.bytesize.to_f
      b = self.bytes
      0.upto(255) do |i|
        x = b.count(i)/sz
        if x > 0
          e += - x * (Math.log(x)/Math.log(2))
        end
      end
      e
    end
  end
end