128-bit data type in C#

Question

In which data type can I store a 128-bit data in c#?

For example

dataType bit128 = 340282366920938463463374607431768211455;

What will be the datatype?

Answer 1

You should consider using BigInteger

https://learn.microsoft.com/en-us/dotnet/api/system.numerics.biginteger?redirectedfrom=MSDN&view=net-6.0

The BigInteger type is an immutable type that represents an arbitrarily large integer whose value in theory has no upper or lower bounds."

string positiveString = "91389681247993671255432112000000";
string negativeString = "-90315837410896312071002088037140000";
BigInteger posBigInt = 0;
BigInteger negBigInt = 0;

try {
   posBigInt = BigInteger.Parse(positiveString);
   Console.WriteLine(posBigInt);
}
catch (FormatException)
{
   Console.WriteLine("Unable to convert the string '{0}' to a BigInteger value.",
                     positiveString);
}

if (BigInteger.TryParse(negativeString, out negBigInt))
  Console.WriteLine(negBigInt);
else
   Console.WriteLine("Unable to convert the string '{0}' to a BigInteger value.",
                      negativeString);

// The example displays the following output:
//   9.1389681247993671255432112E+31
//   -9.0315837410896312071002088037E+34

Answer 2

If you have .NET Core 7.0 Preview 5 or newer than you can simply use System.Int128 or System.UInt128

They were implemented in Add support for Int128 and UInt128 data types

For some reason .NET 7 Preview 5 announcement didn't include those types, but in the upcoming .NET 7 Preview 6 announcement there'll also be Int128Converter and UInt128Converter for the new types in Preview 5

They didn't have C# support yet though, just like System.Half, so you'll have to use Int128 explicitly instead of using a native C# keyword