class PDF::Reader::Filter::RunLength

def filter(data)
  pos = 0
  out = "".dup
  while pos < data.length
    length = data.getbyte(pos)
    pos += 1
    case
    when length == 128
      break
    when length < 128
      # When the length is < 128, we copy the following length+1 bytes
      # literally.
      out << data[pos, length + 1]
      pos += length
    else
      # When the length is > 128, we copy the next byte (257 - length)
      # times; i.e., "\xFA\x00" ([250, 0]) will expand to
      # "\x00\x00\x00\x00\x00\x00\x00".
      out << data[pos, 1] * (257 - length)
    end
    pos += 1
  end
  Depredict.new(@options).filter(out)
end

def initialize(options = {})
  @options = options
end