IPAddr#in6_addr

# File tmp/rubies/ruby-3.3.0/lib/ipaddr.rb, line 668
def in6_addr(left)
  case left
  when RE_IPV6ADDRLIKE_FULL
    if $2
      addr = in_addr($~[2,4])
      left = $1 + ':'
    else
      addr = 0
    end
    right = ''
  when RE_IPV6ADDRLIKE_COMPRESSED
    if $4
      left.count(':') <= 6 or raise InvalidAddressError, "invalid address: #{@addr}"
      addr = in_addr($~[4,4])
      left = $1
      right = $3 + '0:0'
    else
      left.count(':') <= ($1.empty? || $2.empty? ? 8 : 7) or
        raise InvalidAddressError, "invalid address: #{@addr}"
      left = $1
      right = $2
      addr = 0
    end
  else
    raise InvalidAddressError, "invalid address: #{@addr}"
  end
  l = left.split(':')
  r = right.split(':')
  rest = 8 - l.size - r.size
  if rest < 0
    return nil
  end
  (l + Array.new(rest, '0') + r).inject(0) { |i, s|
    i << 16 | s.hex
  } | addr
end