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{ 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; }) hexchars);
in out
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