Floating Point Arithmetic in C#

Question

Hello,

I saw a video tutorial who made in 2014. I wrote the same code in Visual Studio 2022 with C# 10 and I have a true output. but in this movie output is false.
Does have any change occur in floating-point calculation between 2014 and 2022 in .NET?

using System;  
  
namespace ConsoleApp1  
{  
    public class Program  
    {  
        public static void Main(string[] args)  
        {  
            float x = 5.05f;  
            float y = 0.95f;  
  
            Console.WriteLine(x + y);  
            Console.WriteLine("x + y == 6?" + (x + y == 6.0f)); // in video (made in 2014) is false but in C# 10 is true.  
        }  
    }  
}  

Answer 1

In addition to the x86 and x64, the .NET version
seems to be important.

Comparing floating point numbers for equality has always
been discouraged, and there are many references which
explain why and how to correctly handle such
requirements.

https://floating-point-gui.de/errors/comparison/

https://stackoverflow.com/questions/4915462/how-should-i-do-floating-point-comparison

Single.Equals Method
https://learn.microsoft.com/en-us/dotnet/api/system.single.equals?view=net-6.0

"The Equals method should be used with caution,
because two apparently equivalent values can be
unequal due to the differing precision of the
two values. The following example reports that
the Single value .3333 and the Single returned
by dividing 1 by 3 are unequal."

...

"Rather than comparing for equality, one recommended
technique involves defining an acceptable margin of
difference between two values (such as .01% of one
of the values). If the absolute value of the
difference between the two values is less than
or equal to that margin, the difference is likely
to be due to differences in precision and, therefore,
the values are likely to be equal. The following
example uses this technique to compare .33333 and 1/3,
the two Single values that the previous code example
found to be unequal."

...

"The precision of floating-point numbers beyond the
documented precision is specific to the implementation
and version of the .NET Framework. Consequently, a
comparison of two particular numbers might change between
versions of the .NET Framework because the precision of
the numbers' internal representation might change."

• Wayne

Answer 2

The result may depend on the hardware the test is run on. For performance, c# decided that if the hardware used higher precision, then it would accept the results. Originally extra casting code was used, but optimization may remove this code. The jit compiler is more aggressive.

This means depending on optimization you will get different for the same code in different parts of the program.

This is all ok because the spec allows using higher precision then the data type specifies.

Answer 3

In .NET 5, both x86 and x64 generate true.
In .NET 4.7, x86 generate false and x64 generate true.

In addition to the x86 and x64, the .NET version seems to be important.