Add comment for Double_One_Div_LongMaxValue

ICSharpCode.Decompiler.Tests/TestCases/Pretty/WellKnownConstants.cs

@@ -46,8 +46,12 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		public const long LongMaxValue = long.MaxValue;
 		public const long LongMinValue = long.MinValue;
 
+		// This constant is (1 / (double)long.MaxValue). Note that the (double) cast involves
+		// loss of precision: long.MaxValue is rounded up to (long.MaxValue+1), which is a power of two.
+		// The division then is exact, resulting in the double 0x3c00000000000000.
+		// When trying to represent this as a fraction, we get (long.MaxValue+1) as divisor, which
+		// does not fit type long, but compares equals to long.MaxValue due to the long->double conversion.
 		public const double Double_One_Div_LongMaxValue = 1.0842021724855044E-19;
-		public const double Double_One_Div_LongMaxValue_NextDouble = 1.0842021724855047E-19;
 
 		public const float FloatZero = 0f;
 		public const float FloatMinusZero = -0f;