Merge pull request #23 from dmytro-sheyko/master

Fixes #22: Comparison when one of the denominators is negative and both numbers are positive

Author: tompazourek

src/Rationals/Comparisons.cs

@@ -66,12 +66,9 @@ public int CompareTo(Rational other)
         {
             if (Sign == other.Sign)
             {
-                if (Sign >= 0)
-                    return (Numerator * other.Denominator).CompareTo(other.Numerator * Denominator);
-
-                return
-                    -BigInteger.Abs(Numerator * other.Denominator)
-                        .CompareTo(BigInteger.Abs(other.Numerator * Denominator));
+                BigInteger adjDenominator = BigInteger.Abs(Denominator) * other.Denominator.Sign;
+                BigInteger adjOtherDenominator = BigInteger.Abs(other.Denominator) * Denominator.Sign;
+                return (Numerator * adjOtherDenominator).CompareTo(other.Numerator * adjDenominator);
             }
 
             if (Sign > other.Sign)

tests/Rationals.Tests/ComparisonsTests.cs

@@ -60,6 +60,27 @@ public void Comparisons2()
             Assert.True(b <= a);
         }
 
+        [Fact]
+        public void ComparisonsNegativeDenominator()
+        {
+            // arrange
+            var a = new Rational(3);
+            var b = new Rational(-4, -1);
+
+            // assert
+            Assert.Equal(-1, a.CompareTo(b));
+            Assert.False(a > b);
+            Assert.False(a >= b);
+            Assert.True(a < b);
+            Assert.True(a <= b);
+
+            Assert.Equal(+1, b.CompareTo(a));
+            Assert.True(b > a);
+            Assert.True(b >= a);
+            Assert.False(b < a);
+            Assert.False(b <= a);
+        }
+
         [Fact]
         public void Equality1()
         {