1 files changed, 124 insertions, 0 deletions
diff --git a/users/sterni/nix/int/default.nix b/users/sterni/nix/int/default.nix
new file mode 100644
index 000000000000..b3157571272f
--- /dev/null
+++ b/users/sterni/nix/int/default.nix
@@ -0,0 +1,124 @@
+{ depot, lib, ... }:
+
+let
+
+  # TODO(sterni): implement nix.float and figure out which of these
+  #               functions can be split out into a common nix.num
+  #               library.
+
+  inherit (depot.users.sterni.nix)
+    string
+    ;
+
+  inherit (builtins)
+    bitOr
+    bitAnd
+    bitXor
+    mul
+    div
+    add
+    sub
+    ;
+
+  abs = i: if i < 0 then -i else i;
+
+  exp = base: pow:
+    if pow > 0
+    then base * (exp base (pow - 1))
+    else if pow < 0
+    then 1.0 / exp base (abs pow)
+    else 1;
+
+  bitShiftR = bit: count:
+    if count == 0
+    then bit
+    else div (bitShiftR bit (count - 1)) 2;
+
+  bitShiftL = bit: count:
+    if count == 0
+    then bit
+    else 2 * (bitShiftL bit (count - 1));
+
+  hexdigits = "0123456789ABCDEF";
+
+  toHex = int:
+    let
+      go = i:
+        if i == 0
+        then ""
+        else go (bitShiftR i 4)
+           + string.charAt (bitAnd i 15) hexdigits;
+      sign = lib.optionalString (int < 0) "-";
+    in
+      if int == 0
+      then "0"
+      else "${sign}${go (abs int)}";
+
+  fromHexMap = builtins.listToAttrs
+    (lib.imap0 (i: c: { name = c; value = i; })
+      (lib.stringToCharacters hexdigits));
+
+  fromHex = literal:
+    let
+      negative = string.charAt 0 literal == "-";
+      start = if negative then 1 else 0;
+      len = builtins.stringLength literal;
+      # reversed list of all digits
+      digits = builtins.genList
+        (i: string.charAt (len - 1 - i) literal)
+        (len - start);
+      parsed = builtins.foldl'
+        (v: d: {
+          val = v.val + (fromHexMap."${d}" * v.mul);
+          mul = v.mul * 16;
+        })
+        { val = 0; mul = 1; } digits;
+    in
+      if negative
+      then -parsed.val
+      else parsed.val;
+
+  # A nix integer is a 64bit signed integer
+  maxBound = 9223372036854775807;
+
+  # fun fact: -9223372036854775808 is the lower bound
+  # for a nix integer (as you would expect), but you can't
+  # use it as an integer literal or you'll be greeted with:
+  # error: invalid integer '9223372036854775808'
+  # This is because all int literals when parsing are
+  # positive, negative "literals" are positive literals
+  # which are preceded by the arithmetric negation operator.
+  minBound = -9223372036854775807 - 1;
+
+  odd = x: bitAnd x 1 == 1;
+  even = x: bitAnd x 1 == 0;
+
+  # div and mod behave like quot and rem in Haskell,
+  # i. e. they truncate towards 0
+  mod = a: b: let res = a / b; in a - (res * b);
+
+  inRange = a: b: x: x >= a && x <= b;
+
+in {
+  inherit
+    maxBound
+    minBound
+    abs
+    exp
+    odd
+    even
+    add
+    sub
+    mul
+    div
+    mod
+    bitShiftR
+    bitShiftL
+    bitOr
+    bitAnd
+    bitXor
+    toHex
+    fromHex
+    inRange
+    ;
+}