rfc1924

# Takes an IPv6 address as argument
# and encodes it as described in RFC1924.

export LC_ALL=C
export POSIXLY_CORRECT=1
unset BC_ENV_ARGS
unset BC_LINE_LENGTH

d0='0' d10='A' d20='K' d30='U' d40='e' d50='o' d60='y' d70='+' d80='`'
d1='1' d11='B' d21='L' d31='V' d41='f' d51='p' d61='z' d71='-' d81='{'
d2='2' d12='C' d22='M' d32='W' d42='g' d52='q' d62='!' d72=';' d82='|'
d3='3' d13='D' d23='N' d33='X' d43='h' d53='r' d63='#' d73='<' d83='}'
d4='4' d14='E' d24='O' d34='Y' d44='i' d54='s' d64='$' d74='=' d84='~'
d5='5' d15='F' d25='P' d35='Z' d45='j' d55='t' d65='%' d75='>'
d6='6' d16='G' d26='Q' d36='a' d46='k' d56='u' d66='&' d76='?'
d7='7' d17='H' d27='R' d37='b' d47='l' d57='v' d67='(' d77='@'
d8='8' d18='I' d28='S' d38='c' d48='m' d58='w' d68=')' d78='^'
d9='9' d19='J' d29='T' d39='d' d49='n' d59='x' d69='*' d79='_'

bad_address() {
	printf 'invalid address: %s\n' "$addr"
	exit 1
} >&2

addr=$1

case $addr in
*.* )
	tail=${addr##*:}
	head=${addr%"$tail"}

	case $tail in
	'' | *[!0-9.]* )
		bad_address ;;
	.* | *..* | *. | *.*.*.*.* )
		bad_address ;;
	*[!.][!.][!.][!.]* )
		bad_address ;;
	*.*.*.* ) ;;
	* )
		bad_address
	esac

	tail16=$(
		IFS=.
		for d in $tail; do
			if test $d -gt 255; then
				bad_address
			fi

			printf '%02X' $d
		done
	)
	addr=$head${tail16%????}:${tail16#????}
esac

case $addr in
'' | *[!0-9A-Fa-f:]* )
	bad_address ;;
*:::* | *::*::* | *:*:*:*:*:*:*:*:* )
	bad_address ;;
*[!:][!:][!:][!:][!:]* )
	bad_address ;;
*::* ) ;;
*[!:]*:*:*:*:*:*:*:*[!:]* ) ;;
* )
	bad_address
esac

case $addr in
*::* )
	case $addr in
	:: )
		addr=0${addr}0 ;;
	::* )
		addr=0$addr ;;
	*:: )
		addr=${addr}0
	esac

	head=${addr%%::*}
	tail=${addr#"$head":}

	while true; do
		case $head$tail in
		*:*:*:*:*:*:*:* )
			break ;;
		* )
			tail=:0$tail
		esac
	done

	addr=$head$tail
esac

addr16=$(
	IFS=:
	for d in $addr; do
		printf '%04X' 0x$d
	done
)

rem85=$(bc <<eof
ibase = 16
q = $addr16
ibase = A
for (i = 0; i < 20; i++) {
	r = q % 85
	q -= r
	q /= 85
	r
}
eof
)

addr85=
for d in $rem85; do
	eval "addr85=\$(printf '%c' \$d$d)\$addr85"
done

printf '%s\n' "$addr85"

# vim: ft=sh