lib/net.sh: add net_netmask_to_prefix

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/net.sh b/lib/net.sh
new file mode 100644
index 0000000..518c955
--- /dev/null
+++ b/lib/net.sh
@@ -0,0 +1,9 @@
+net_netmask_to_prefix() {(
+  binaryNetmask=$(echo $1 | sed 's/^/obase=2;/;s/\./;/g' | bc | tr -d \\n)
+  binaryPrefix=$(echo $binaryNetmask | sed -n 's/^\(1*\)0*$/\1/p')
+  if ! echo $binaryPrefix | grep -q .; then
+    echo $0: bad netmask: $netmask >&2
+    exit 4
+  fi
+  printf %s $binaryPrefix | tr -d 0 | wc -c
+)}