feat(users/sterni/nix): add sternis nix lib r/2257

What you see here is mostly the fallout of me implementing a correct
urlencode implementation in nix for Profpatsch's blog implementation
(although they'll probably keep it at arm's length).

Where I want to go from here:

* Extend this library towards general purpose nix™, mainly by
  implementing missing interfaces which you'd still have to use
  <nixpkgs/lib> for right now. Reexposing parts of <nixpkgs/lib>
  with better naming is fine for now, at some point I'd contemplate
  making this depend on nothing outside of depot, maybe even itself
  (should be easy we only use yants for an easily replaceable check).

* Improve error messages possibly by carefully reintroducing yants. I
  originally typed essentially everything using yants, but turns out
  this can a) be dangerous when stuff you are handling throws because
  type checking means evaluating and b) has a incredible performance
  cost in some cases.

* Reexpose builtins with better naming and slightly wrapped so they
  don't unrecoverably throw in cases where a null or something would
  suffice.

Change-Id: I33ab08ca4e62dbc16b86c66c653935686e6b0e79
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2541
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: Profpatsch <mail@profpatsch.de>
Tested-by: BuildkiteCI

1 files changed, 121 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..cd46fe7864d1
--- /dev/null
+++ b/users/sterni/nix/int/default.nix
@@ -0,0 +1,121 @@
+{ 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);
+
+in {
+  inherit
+    maxBound
+    minBound
+    abs
+    exp
+    odd
+    even
+    add
+    sub
+    mul
+    div
+    mod
+    bitShiftR
+    bitShiftL
+    bitOr
+    bitAnd
+    bitXor
+    toHex
+    fromHex
+    ;
+}