Converting from number of IP addresses to a /notation using awk

gistfile1.txt

# easy case where /24 is the smallext allocation  $1 is the number

$ echo 8192 | awk '{print 32-log($1)/log(2)}'
13
$ echo 32 | awk '{print 32-log($1)/log(2)}'
5

# this can be used to convert 1.2.4.0   8192 to 1.2.3.0/19
$ echo 1.2.4.0   8192 | awk '{print $"/"32-log($2)/log(2)}'
1.2.3.0/19