$6$

last string digit is even

divides by $3$

$8$

Version $1$

is the last string digit even $(0,2,4,6,8)$

divide by $2($convert to number, divide, return to string$)$

is the new value even

divide by $2($convert to number, divide, return to string$)$

is the new value even

version $2$

look at last bit, is it $0$

bit shift left

is the last bit $0?$

bit shift left

is the last bit $0?$

version $3$

are the last $3$ bits $000--$ this masks the last $3$ bits $($ not$($ bit & $7))$

$9$

version $1$

is if divisible by $3($see above$)$

divide by $3$

is the new result divisible by $3$

version $2$

using the algorithm for divide by $3,$ test to see if the final single digit string is $0$ or $9$