Fix for negative feet/inch parsing (#674)

* Fix for negative feet/inch parsing

Author: tmilnthorp

UnitsNet.Tests/CustomCode/LengthTests.FeetInches.cs

@@ -41,6 +41,17 @@ public void FeetInchesRoundTrip()
         [InlineData("1′1″", 1.08333333)] // Without space
         [InlineData("1 ft 1 in", 1.08333333)]
         [InlineData("1ft 1in", 1.08333333)]
+        [InlineData("-1'", -1)] // Feet only
+        [InlineData("-1′", -1)] // Feet only
+        [InlineData("-1\"", -0.08333333)] // Inches only
+        [InlineData("-1″", -0.08333333)] // Inches only
+        [InlineData("-1' 1\"", -1.08333333)] // Normal form
+        [InlineData("-1′ 1″", -1.08333333)] // Normal form
+        [InlineData(" -1′ 1″ ", -1.08333333)] // Normal form, requires trimming
+        [InlineData("-1'1\"", -1.08333333)] // Without space
+        [InlineData("-1′1″", -1.08333333)] // Without space
+        [InlineData("-1 ft 1 in", -1.08333333)]
+        [InlineData("-1ft 1in", -1.08333333)]
         public void TryParseFeetInches(string str, double expectedFeet)
         {
             Assert.True(Length.TryParseFeetInches(str, out Length result));

UnitsNet/CustomCode/Quantities/Length.extra.cs

@@ -98,7 +98,7 @@ public static bool TryParseFeetInches([CanBeNull] string str, out Length result,
             if (TryParse(feetGroup.Value, formatProvider, out Length feet) &&
                 TryParse(inchesGroup.Value, formatProvider, out Length inches))
             {
-                result = feet + inches;
+                result = feet.Value >= 0 ? feet + inches : feet - inches;
                 return true;
             }