class FakeFS::File

def extract_binmode(opts, fmode)
  textmode = opts[:textmode]
  unless textmode.nil?
    raise ArgumentError, "textmode specified twice" if fmode & FMODE_TEXTMODE != 0
    raise ArgumentError, "both textmode and binmode specified" if fmode & FMODE_BINMODE != 0
    # yep, false has no effect here, but still causes ArgumentError
    fmode |= FMODE_TEXTMODE if textmode
  end
  binmode = opts[:binmode]
  unless binmode.nil?
    raise ArgumentError, "binmode specified twice" if fmode & FMODE_BINMODE != 0
    raise ArgumentError, "both textmode and binmode specified" if fmode & FMODE_TEXTMODE != 0
    fmode |= FMODE_BINMODE if binmode
  end
  if fmode & FMODE_BINMODE != 0 && fmode & FMODE_TEXTMODE != 0
    raise ArgumentError, "both textmode and binmode specified"
  end
  fmode
end