Fix BigInteger.Rotate{Left,Right}

[kzrnm]

Fix #112854

• Fixed the logic of RotateRight.
• Fixed a bug that caused incorrect two’s complement computation for negative numbers with the most significant bit set in RotateRight and RotateLeft.

I reused the code from #112632.

Benchmark

Code

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using System.Numerics;

[MemoryDiagnoser(false)]
[HideColumns("Job", "Error", "StdDev", "Median", "RatioSD")]
public class RotateTest
{
    const int shiftSize = (1 << 23) + 13;
    BigInteger positive, negative;

    [GlobalSetup]
    public void Setup()
    {
        var bytes = new byte[1 << 25];
        new Random(227).NextBytes(bytes);
        positive = new BigInteger(bytes, isUnsigned: true);
        negative = -positive;
    }

    [Benchmark] public BigInteger PositiveRotateLeft() => BigInteger.RotateLeft(positive, shiftSize);
    [Benchmark] public BigInteger NegativeRotateLeft() => BigInteger.RotateLeft(negative, shiftSize);

    [Benchmark] public BigInteger PositiveRotateRight() => BigInteger.RotateRight(positive, shiftSize);
    [Benchmark] public BigInteger NegativeRotateRight() => BigInteger.RotateRight(negative, shiftSize);
}

BenchmarkDotNet v0.13.12, Windows 11 (10.0.26100.3194)
13th Gen Intel Core i5-13500, 1 CPU, 20 logical and 14 physical cores
.NET SDK 10.0.100-alpha.1.25077.2
  [Host]     : .NET 10.0.0 (10.0.25.7313), X64 RyuJIT AVX2
  Job-JFZQTT : .NET 10.0.0 (42.42.42.42424), X64 RyuJIT AVX2
  Job-RFISUH : .NET 10.0.0 (42.42.42.42424), X64 RyuJIT AVX2

Method	Toolchain	Mean	Ratio	Gen0	Gen1	Gen2	Allocated	Alloc Ratio
PositiveRotateLeft	\main\corerun.exe	19.15 ms	1.00	156.2500	156.2500	156.2500	33 MB	1.00
PositiveRotateLeft	\pr\corerun.exe	14.10 ms	0.61	218.7500	218.7500	218.7500	32.69 MB	0.99
NegativeRotateLeft	\main\corerun.exe	19.35 ms	1.00	156.2500	156.2500	156.2500	33 MB	1.00
NegativeRotateLeft	\pr\corerun.exe	18.59 ms	0.96	218.7500	218.7500	218.7500	33.25 MB	1.01
PositiveRotateRight	\main\corerun.exe	14.93 ms	1.00	156.2500	156.2500	156.2500	32.5 MB	1.00
PositiveRotateRight	\pr\corerun.exe	14.07 ms	0.94	234.3750	234.3750	234.3750	32.73 MB	1.01
NegativeRotateRight	\main\corerun.exe	16.92 ms	1.00	156.2500	156.2500	156.2500	33 MB	1.00
NegativeRotateRight	\pr\corerun.exe	16.43 ms	0.97	218.7500	218.7500	218.7500	33.25 MB	1.01

[tannergooding]

Can this initially be done as a smaller fix that doesn't rewrite the whole algorithm?

We likely need to backport this fix and a less complex change is more desirable for that, as it reduces risk.

A separate PR that also rewrites it for improved performance just for .NET 10 is fine, just ideally separate from the bug fix.

[kzrnm]

#112878