short_string_packer.rb

class ShortStringPacker
  ## Packs a short string into a Fixnum
  # Arguments:
  #   str - String object
  # Returns: a Fixnum object
  def self.pack(str, nb_bits=5)
    res = 0
    str.each_char.with_index do |char, index|
      res = res | ((char.ord - 'a'.ord + 1)  << nb_bits*(str.length-(index+1)))
    end
    res
  end

  ## Unpacks a Fixnum from pack() method into a short string
  # Arguments:
  #   packed - a Fixnum object
  # Returns: a String object
  def self.unpack(packed, nb_bits=5)
    res = ""
    mask = (2 ** nb_bits) - 1
    (0..packed.to_s(2).length-1).step(nb_bits).reverse_each do |i| 
      res += (((packed & (mask << i)) >> i) + 'a'.ord - 1) .chr
    end
    res
  end
end