sh Arithmetic Expansion Is a Power of 2
Example
$ ispow2() { return $((!($1!=0&&($1&$1-1)==0))); }
$ i=0
$ while [ $i -lt 100 ]; do
> if ispow2 $((i=i+1)); then
> echo $i
> fi
> done
1
2
4
8
16
32
64
$1!=0 0 is not a power of 2.
($1&$1-1)==0 Unset the lowest bit. If it was the only bit then the number was a power of 2.
The additional ! was for correcting the value to what the shell expects, which is the opposite of the conventional true/false values
(zero for true and non-zero for false, vs zero for false and non-zero for true).
