add slaacSuffix to unused lib

nix/lib/default.nix

@@ -10,6 +10,8 @@ libO
 
   types = libO.types // lib.importFlakeMod ./types.nix;
 
+  x-banananetwork-unused = lib.importFlakeMod ./unused.nix;
+
   # functions
 
   supportedSystems = builtins.attrNames nixpkgs.legacyPackages;

nix/lib/unused.nix

@@ -0,0 +1,49 @@
+{ lib, ... }@flakeArg:
+# functions I wrote but didn’t end up using
+# feel free to use them & reference them directly
+{
+
+  slaacSuffix =
+    mac:
+    let
+      replaceChars = [
+        " "
+        "."
+        ":"
+        "-"
+      ];
+      rawMac = builtins.replaceStrings replaceChars (map (x: "") replaceChars) (lib.strings.toLower mac);
+      invert7bit = {
+        "0" = "2";
+        "1" = "3";
+        "2" = "0";
+        "3" = "1";
+        "4" = "6";
+        "5" = "7";
+        "6" = "4";
+        "7" = "5";
+        "8" = "a";
+        "9" = "b";
+        "a" = "8";
+        "b" = "9";
+        "c" = "e";
+        "d" = "f";
+        "e" = "c";
+        "f" = "d";
+      };
+      inherit (builtins) substring;
+    in
+    assert builtins.match (lib.strings.replicate 12 "[0-9a-f]") rawMac;
+    builtins.concatStringsSep "" [
+      (substring 0 1 rawMac)
+      (invert7bit.${substring 1 1 rawMac})
+      (substring 2 2 rawMac)
+      ":"
+      (substring 4 2 rawMac)
+      "ff:f0"
+      (substring 6 2 rawMac)
+      ":"
+      (substring 8 4 rawMac)
+    ];
+
+}