lib/math: init subset

Just copied over from Bahaghari lul

lib/default.nix

@@ -17,11 +17,12 @@ pkgs.lib.makeExtensible
     builders = callLib ./builders;
     trivial = callLib ./trivial.nix;
     data = callLib ./data.nix;
+    math = callLib ./math.nix;
     fetchers = callLib ./fetchers;
 
     inherit (self.builders) makeXDGMimeAssociationList
       makeXDGPortalConfiguration makeXDGDesktopEntry;
-    inherit (self.trivial) countAttrs;
+    inherit (self.trivial) countAttrs filterAttrs';
     inherit (self.data) importYAML renderTeraTemplate renderMustacheTemplate;
     inherit (self.fetchers) fetchInternetArchive;
   } // lib.optionalAttrs (builtins ? fetchTree) {

lib/math.nix

@@ -0,0 +1,37 @@
+# Math subset.
+{ pkgs, lib, self }:
+
+rec {
+  /* Returns the absolute value of the given number.
+
+     Example:
+       abs -4
+       => 4
+
+       abs (1 / 5)
+       => 0.2
+  */
+  abs = number:
+    if number < 0 then -(number) else number;
+  /* Exponentiates the given base with the exponent.
+
+     Example:
+       pow 2 3
+       => 8
+
+       pow 6 4
+       => 1296
+  */
+  pow = base: exponent:
+    # Just to be a contrarian, I'll just make this as a tail recursive function
+    # instead lol.
+    let
+      absValue = abs exponent;
+      iter = product: counter: maxCount:
+        if counter > maxCount
+        then product
+        else iter (product * base) (counter + 1) maxCount;
+      value = iter 1 1 absValue;
+    in
+    if exponent < 0 then (1 / value) else value;
+}

tests/lib/default.nix

@@ -20,6 +20,7 @@ in
   builders = callLib ./builders.nix;
   trivial = callLib ./trivial.nix;
   data = callLib ./data;
+  math = callLib ./math.nix;
 
   # Environment-specific subset.
   home-manager = callLib ./home-manager.nix;

tests/lib/math.nix

@@ -0,0 +1,34 @@
+{ pkgs, lib, self }:
+
+
+lib.runTests {
+  testMathAbsoluteValue = {
+    expr = self.math.abs 5493;
+    expected = 5493;
+  };
+
+  testMathAbsoluteValue2 = {
+    expr = self.math.abs (-435354);
+    expected = 435354;
+  };
+
+  testMathPowPositive = {
+    expr = self.math.pow 2 8;
+    expected = 256;
+  };
+
+  testMathPowNegative = {
+    expr = self.math.pow 2.0 (-1);
+    expected = 0.5;
+  };
+
+  testMathPowZero = {
+    expr = self.math.pow 31 0;
+    expected = 1;
+  };
+
+  testsMathPowWithFloat = {
+    expr = self.math.pow 2 7.0;
+    expected = 128.0;
+  };
+}