bscco.rb

# Caculate the BSCCO checksum for a file
# Usage: `$ ruby bscco.rb your_file.txt`
# Based on the algorithm description in https://www.elexon.co.uk/wp-content/uploads/2013/11/bscp533_appx_a_v17.0.pdf
def bscco(file)
  lines_except_last = File.read(file).lines[0..-2]

  lines_as_bytes = lines_except_last
    .map(&:chomp)
    .map(&:bytes)
    .map do |line_bytes|
      unless (remainder = line_bytes.length % 4) == 0
        # pad with 0s so it is a multiple of 4
        line_bytes += [0] * (4 - remainder)
      end
      line_bytes
    end

  file_contents = lines_as_bytes.flatten.to_a

  num_chars = file_contents.length

  checksum = file_contents.each_slice(4).inject(0) do |chk, cur_bytes|
    current_word = cur_bytes.inject(0) { |initial, cur_byte| (initial << 8) + cur_byte }
    chk ^ current_word
  end

  checksum
end

file_path = ARGV.shift

checksum = bscco(file_path)

puts "#{file_path} #{checksum}"