Added function cidr2mask in .zshrc

.zshrc

@@ -16,6 +16,43 @@ gbranch() {
     echo -e "$(git branch "$@")"
 }
 
+mask2cidr() {
+    local mask=$1
+
+    # In RFC 4632 netmasks there's no "255." after a non-255 byte in the mask
+    local left_stripped_mask=${mask##*255.}
+    local len_mask=${#mask}
+    local len_left_stripped_mask=${#left_stripped_mask}
+
+    local conversion_table=0^^^128^192^224^240^248^252^254^
+    local number_of_bits_stripped=$((($len_mask - $len_left_stripped_mask) * 2))
+    local signifacant_octet=${left_stripped_mask%%.*}
+
+    local right_stripped_conversion_table=${conversion_table%%$signifacant_octet*}
+    local len_right_stripped_conversion_table=${#right_stripped_conversion_table}
+    local number_of_bits_from_conversion_table=$((len_right_stripped_conversion_table / 4))
+    echo $(($number_of_bits_stripped + $number_of_bits_from_conversion_table))
+}
+
+cidr2mask() {
+    local i mask=""
+    local full_octets=$(($1 / 8))
+    local partial_octet=$(($1 % 8))
+
+    for ((i = 0; i < 4; i += 1)); do
+        if [ $i -lt $full_octets ]; then
+            mask+=255
+        elif [ $i -eq $full_octets ]; then
+            mask+=$((256 - 2 ** (8 - $partial_octet)))
+        else
+            mask+=0
+        fi
+        test $i -lt 3 && mask+=.
+    done
+
+    echo $mask
+}
+
 [ -f /etc/gentoo-release ] && export ZSH="/usr/share/zsh/site-contrib/oh-my-zsh"
 [ -f /etc/centos-release ] && export ZSH="$HOME/.oh-my-zsh"
 [ -f /etc/debian_version ] && export ZSH="$HOME/.oh-my-zsh"