diff --git a/default.inc b/default.inc
index 9246837..737e82d 100755
--- a/default.inc
+++ b/default.inc
@@ -28,6 +28,12 @@ containsElement () {
 
 function join_by { local IFS="$1"; shift; echo "$*"; }
 
+IPprefix_by_netmask () { 
+   c=0 x=0$( printf '%o' ${1//./ } )
+   while [ $x -gt 0 ]; do
+       let c+=$((x%2)) 'x>>=1'
+   done
+   echo /$c ; }
 
 if type apt &>/dev/null; then
 	ATYPE="apt"