align port range to 2^n start and 2^n-1 size for smallest n

rangealign.sh

#!/bin/bash
# align port range to 2^n start and 2^n-1 size for smallest n
# call: rangealign.sh a-b

a=${1%-*}
b=${1##*-}
dist=$((b-a))
n=2
while [ $dist -ge $((2**n)) ]; do
	((++n));
done
n2=$((2**n))

start=$((a - a % (2**n)))
while [ $((start + 2**n - 1)) -lt $b ]; do
	# echo "$dist $n $((2**n)) $start-$(($start + 2**n - 1)) ($a-$b)"
	((++n))
	start=$((a - a % (2**n)))
done

# echo "$dist $n $((2**n)) $start-$(($start + 2**n - 1)) ($a-$b)"
echo "$start-$(($start + 2**n - 1))"