BigInteger.TryParse incorrectly parses "80000000" from hex as -4294967295

[rjmholt]

Description

From PowerShell/PowerShell#15587.

Possibly related to #50385?

However, in this case this behaviour represents a regression from .NET 6 preview 5.

Repro:

using System;
using System.Diagnostics;
using System.Globalization;
using System.Numerics;
using System.Runtime.InteropServices;

namespace repro
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($".NET: '{RuntimeInformation.FrameworkDescription}'");

            string numStr = args.Length > 0
                ? args[0]
                : "80000000";

            BigInteger.TryParse(numStr, NumberStyles.AllowHexSpecifier, NumberFormatInfo.InvariantInfo, out BigInteger bi);

            Console.WriteLine($"Expected: '{numStr}'");
            Console.WriteLine($"Actual: '{bi.ToString("X")}'");

            Debug.Assert(bi.ToString("X") == numStr);
        }
    }
}

Configuration

x64 Windows PC:

OS Name:                   Microsoft Windows 10 Pro
OS Version:                10.0.19043 N/A Build 19043

> dotnet version
6.0.100-preview.5.21302.13

Regression?

This previously worked in .NET 6 preview 4.

Other information

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-numerics
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

From PowerShell/PowerShell#15587.

Possibly related to #50385?

However, in this case this behaviour represents a regression from .NET 6 preview 5.

Repro:

using System;
using System.Diagnostics;
using System.Globalization;
using System.Numerics;
using System.Runtime.InteropServices;

namespace repro
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($".NET: '{RuntimeInformation.FrameworkDescription}'");

            string numStr = args.Length > 0
                ? args[0]
                : "80000000";

            BigInteger.TryParse(numStr, NumberStyles.AllowHexSpecifier, NumberFormatInfo.InvariantInfo, out BigInteger bi);

            Console.WriteLine($"Expected: '{numStr}'");
            Console.WriteLine($"Actual: '{bi.ToString("X")}'");

            Debug.Assert(bi.ToString("X") == numStr);
        }
    }
}

Configuration

x64 Windows PC:

OS Name:                   Microsoft Windows 10 Pro
OS Version:                10.0.19043 N/A Build 19043

> dotnet version
6.0.100-preview.5.21302.13

Regression?

This previously worked in .NET 6 preview 4.

Other information

Author:	rjmholt
Assignees:	-
Labels:	area-System.Numerics, untriaged
Milestone:	-

[rjmholt]

Looks like this was fixed in #54262.