bahaghari/lib: simplify math.remainder

Indeed I'm too dumb for mathematics. :p

Also, now the remainder implementation is double-checked with Python 3's
math.remainder() function.

subprojects/bahaghari/lib/math.nix

@@ -253,8 +253,8 @@ rec {
       floor (difference + 0.5) * nearest;
 
   /* Similar to the nixpkgs' `trivial.mod` but retain the decimal values. This
-     is just an approximation from ECMAScript's implementation of the modulo
-     operator (%) which is more like a remainder operator.
+     is just an approximation from ECMAScript's implementation of the remainder
+     operator.
 
      Type: remainder :: Number -> Number -> Number
 
@@ -274,20 +274,11 @@ rec {
        remainder (-54) (-4)
        => -2
   */
-  remainder = base: number:
+  remainder = dividend: divisor:
     let
-      base' = abs base;
-      number' = abs number;
-      difference = number' * ((floor (base' / number')) + 1);
-
-      result = abs (number' - (difference - base'));
+      quotient = dividend / divisor;
     in
-      if number' > base'
-      then base
-      else
-        if base < 0
-        then -(result)
-        else result;
+      dividend - ((floor quotient) * divisor);
 
   /* Adds all of the given items on the list starting from a sum of zero.
 

subprojects/bahaghari/tests/lib/math.nix

@@ -268,22 +268,22 @@ lib.runTests {
     expected = 0.5;
   };
 
-  testMathRemainderBothPositive = {
+  testMathRemainderPositiveOperands = {
     expr = self.math.remainder 54.5 20.5;
     expected = 13.5;
   };
 
-  testMathRemainderNegativeBase = {
+  testMathRemainderNegativeDividend = {
     expr = self.math.remainder (-54.5) 20.5;
-    expected = -13.5;
+    expected = 7;
   };
 
-  testMathRemainderNegativeNumber = {
+  testMathRemainderNegativeDivisor = {
     expr = self.math.remainder 54.5 (-20.5);
-    expected = 13.5;
+    expected = -7;
   };
 
-  testMathRemainderBothNegatives = {
+  testMathRemainderNegativeOperands = {
     expr = self.math.remainder (-54.5) (-20.5);
     expected = -13.5;
   };