{pkgs => lib}.genid

2 files changed, 40 insertions, 0 deletions

diff --git a/krebs/4lib/default.nix b/krebs/4lib/default.nix
index 1cabeae2..dfc51bbe 100644
--- a/krebs/4lib/default.nix
+++ b/krebs/4lib/default.nix
@@ -7,6 +7,8 @@ let out = rec {
 
   eq = x: y: x == y;
 
+  mod = x: y: x - y * (x / y);
+
   addName = name: set:
     set // { inherit name; };
 
@@ -17,6 +19,7 @@ let out = rec {
   dir.has-default-nix = path: pathExists (path + "/default.nix");
 
   dns = import ./dns.nix { inherit lib; };
+  genid = import ./genid.nix { lib = lib // out; };
   git = import ./git.nix { lib = lib // out; };
   listset = import ./listset.nix { inherit lib; };
   shell = import ./shell.nix { inherit lib; };
diff --git a/krebs/4lib/genid.nix b/krebs/4lib/genid.nix
new file mode 100644
index 00000000..0aed1d35
--- /dev/null
+++ b/krebs/4lib/genid.nix
@@ -0,0 +1,37 @@
+{ lib, ... }:
+with lib;
+with builtins;
+let out = genid;
+
+  # id = genid s = (hash s + min) % max
+  # min <= genid s < max
+  #
+  # min = 2^24 =   16777216 = 0x001000000
+  # max = 2^32 = 4294967296 = 0x100000000
+  #
+  # id is bigger than UID of nobody and GID of nogroup
+  # see <nixos/modules/misc/ids.nix> and some spare for stuff like lxd.
+  #
+  # :: str -> uint32
+  genid = s: sum16 (addmod16_16777216 (hash s));
+
+  # :: str -> list8 uint4
+  hash = s:
+    map hexint (stringToCharacters (substring 32 8 (hashString "sha1" s)));
+
+  # :: list uint -> uint
+  sum16 = foldl (a: i: a * 16 + i) 0;
+
+  # :: list8 uint4 -> list1 uint8 ++ list6 uint4
+  addmod16_16777216 = x: let
+    a = 16 * head x + head (tail x);
+    d = tail (tail x);
+  in [(mod (a + 1) 256)] ++ d;
+
+  # :: char -> uint4
+  hexint = x: hexvals.${toLower x};
+
+  # :: attrset char uint4
+  hexvals = listToAttrs (imap (i: c: { name = c; value = i - 1; })
+                        (stringToCharacters "0123456789abcdef"));
+in out