Gem::Package::TarHeader.oct_or_256based

# File tmp/rubies/ruby-3.0.5/lib/rubygems/package/tar_header.rb, line 132
def self.oct_or_256based(str)
  # \x80 flags a positive 256-based number
  # \ff flags a negative 256-based number
  # In case we have a match, parse it as a signed binary value
  # in big-endian order, except that the high-order bit is ignored.
  return str.unpack('N2').last if str =~ /\A[\x80\xff]/n
  strict_oct(str)
end