using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Linq.Expressions;

using System.Numerics;

using System.Reflection;

using System.Runtime.CompilerServices;

​

class Program

{

    const int Iterations = 5_000_000;

​

    static void Main()

    {

        var bitSizes = new[] { 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536 };

​

        Console.WriteLine($"Running {Iterations:N0} iterations per method for each BigInteger size...\n");

        Console.WriteLine($"{"Bits",6} | {"Mask & Cast",12} | {"ToByteArray->BitConv",20} | {"Reflection",10} | {"Compile", 7}");

​

        foreach (int bits in bitSizes)

        {

            BigInteger bigPos = BigInteger.One << (bits - 1); // e.g. 2^(n-1)

            BigInteger bigNeg = -bigPos;

​

            Warmup(bigPos, bigNeg);

​

            // Measure each method

            long acc1 = 0, acc2 = 0, acc3 = 0, acc4 = 0;

​

            var sw1 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc1 += MaskToInt((i & 1) == 0 ? bigPos : bigNeg);

            sw1.Stop();

​

            var sw2 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc2 += ((i & 1) == 0 ? bigPos : bigNeg).ToInt();

            sw2.Stop();

​

            var sw3 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc3 += ((i & 1) == 0 ? bigPos : bigNeg).ToInt32Truncate();

            sw3.Stop();

​

            var sw4 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc4 += ((i & 1) == 0 ? bigPos : bigNeg).ToInt32TruncateCompiled();

            sw4.Stop();

​

            if (acc1 != acc2 || acc1 != acc3 || acc1 != acc4)

            {

                Console.WriteLine($"Error: Results mismatch for {bits} bits!");

                return;

            }

            Console.WriteLine($"{bits,6} | {sw1.ElapsedMilliseconds,12:N0} | {sw2.ElapsedMilliseconds,20:N0} | {sw3.ElapsedMilliseconds,10:N0} | {sw4.ElapsedMilliseconds,7:N0}");

        }

​

        Console.WriteLine("\nDone.");

    }

​

    static void Warmup(BigInteger p, BigInteger n)

    {

        for (int i = 0; i < 1000; i++)

        {

            _ = MaskToInt(p);

            _ = MaskToInt(n);

            _ = p.ToInt();

            _ = n.ToInt();

            _ = p.ToInt32Truncate();

            _ = n.ToInt32Truncate();

            _ = p.ToInt32TruncateCompiled();

            _ = n.ToInt32TruncateCompiled();

        }

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    static int MaskToInt(BigInteger big) => unchecked((int)(uint)(big & uint.MaxValue));

}

​

public static class BigIntegerToByteArrayExtensions

{

    public static int ToInt(this BigInteger big)

    {

        return BitConverter.ToInt32(big.ToByteArray().AsSpan(0, 4));

    }

}

​

public static class BigIntegerExtensions

{

    private static readonly FieldInfo s_signField;

    private static readonly FieldInfo s_bitsField;

​

    static BigIntegerExtensions()

    {

        s_signField = typeof(BigInteger)

            .GetField("_sign", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new Exception("Could not find BigInteger._sign field");

​

        s_bitsField = typeof(BigInteger)

            .GetField("_bits", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new Exception("Could not find BigInteger._bits field");

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static uint ToUInt32Truncate(this BigInteger value)

    {

        if (value.GetBitLength() < 256)

        {

            return BitConverter.ToUInt32(value.ToByteArray().AsSpan(0, 4));

        }

​

        uint[]? magnitude = (uint[]?)s_bitsField.GetValue(value);

        int sign = (int)s_signField.GetValue(value)!;

​

        if (magnitude is null)

        {

            if (sign >= 0)

                return (uint)sign;

​

            unchecked

            {

                uint absSign = (uint)(-sign);

                return (uint)(~absSign + 1);

            }

        }

​

        uint lowWord = magnitude.Length > 0 ? magnitude[0] : 0u;

        return sign > 0 ? lowWord : unchecked((uint)(~lowWord + 1));

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static int ToInt32Truncate(this BigInteger value)

    {

        uint u = value.ToUInt32Truncate();

        return unchecked((int)u);

    }

}

​

public static class BigIntegerCompiledAccess

{

    public static readonly Func<BigInteger, int> GetSign;

    public static readonly Func<BigInteger, uint[]?> GetBits;

​

    static BigIntegerCompiledAccess()

    {

        // Expression: (BigInteger x) => x._sign

        var param = Expression.Parameter(typeof(BigInteger), "x");

​

        var signField = typeof(BigInteger)

            .GetField("_sign", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new InvalidOperationException("Field '_sign' not found");

​

        var bitsField = typeof(BigInteger)

            .GetField("_bits", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new InvalidOperationException("Field '_bits' not found");

​

        GetSign = Expression.Lambda<Func<BigInteger, int>>(

            Expression.Field(param, signField), param).Compile();

​

        GetBits = Expression.Lambda<Func<BigInteger, uint[]?>>(

            Expression.Field(param, bitsField), param).Compile();

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static uint ToUInt32TruncateCompiled(this BigInteger value)

    {

        if (value.IsZero) return 0u;

​

        int sign = BigIntegerCompiledAccess.GetSign(value);

        uint[]? magnitude = BigIntegerCompiledAccess.GetBits(value);

​

        if (magnitude is null)

        {

            if (sign >= 0) return (uint)sign;

            unchecked

            {

                uint absSign = (uint)(-sign);

                return (uint)(~absSign + 1);

            }

        }

​

        uint lowWord = magnitude.Length > 0 ? magnitude[0] : 0u;

        return sign > 0 ? lowWord : unchecked((uint)(~lowWord + 1));

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static int ToInt32TruncateCompiled(this BigInteger value)

    {

        return unchecked((int)value.ToUInt32TruncateCompiled());

    }

}using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Linq.Expressions;

using System.Numerics;

using System.Reflection;

using System.Runtime.CompilerServices;

​

class Program

{

    const int Iterations = 5_000_000;

​

    static void Main()

    {

        var bitSizes = new[] { 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536 };

​

        Console.WriteLine($"Running {Iterations:N0} iterations per method for each BigInteger size...\n");

        Console.WriteLine($"{"Bits",6} | {"Mask & Cast",12} | {"ToByteArray->BitConv",20} | {"Reflection",10} | {"Compile", 7}");

​

        foreach (int bits in bitSizes)

        {

            BigInteger bigPos = BigInteger.One << (bits - 1); // e.g. 2^(n-1)

            BigInteger bigNeg = -bigPos;

​

            Warmup(bigPos, bigNeg);

​

            // Measure each method

            long acc1 = 0, acc2 = 0, acc3 = 0, acc4 = 0;

​

            var sw1 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc1 += MaskToInt((i & 1) == 0 ? bigPos : bigNeg);

            sw1.Stop();

​

            var sw2 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc2 += ((i & 1) == 0 ? bigPos : bigNeg).ToInt();

            sw2.Stop();

​

            var sw3 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc3 += ((i & 1) == 0 ? bigPos : bigNeg).ToInt32Truncate();

            sw3.Stop();

​

            var sw4 = Stopwatch.StartNew();

            for (int i = 0; i < Iterations; i++)

                acc4 += ((i & 1) == 0 ? bigPos : bigNeg).ToInt32TruncateCompiled();

            sw4.Stop();

​

            if (acc1 != acc2 || acc1 != acc3 || acc1 != acc4)

            {

                Console.WriteLine($"Error: Results mismatch for {bits} bits!");

                return;

            }

            Console.WriteLine($"{bits,6} | {sw1.ElapsedMilliseconds,12:N0} | {sw2.ElapsedMilliseconds,20:N0} | {sw3.ElapsedMilliseconds,10:N0} | {sw4.ElapsedMilliseconds,7:N0}");

        }

​

        Console.WriteLine("\nDone.");

    }

​

    static void Warmup(BigInteger p, BigInteger n)

    {

        for (int i = 0; i < 1000; i++)

        {

            _ = MaskToInt(p);

            _ = MaskToInt(n);

            _ = p.ToInt();

            _ = n.ToInt();

            _ = p.ToInt32Truncate();

            _ = n.ToInt32Truncate();

            _ = p.ToInt32TruncateCompiled();

            _ = n.ToInt32TruncateCompiled();

        }

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    static int MaskToInt(BigInteger big) => unchecked((int)(uint)(big & uint.MaxValue));

}

​

public static class BigIntegerToByteArrayExtensions

{

    public static int ToInt(this BigInteger big)

    {

        return BitConverter.ToInt32(big.ToByteArray().AsSpan(0, 4));

    }

}

​

public static class BigIntegerExtensions

{

    private static readonly FieldInfo s_signField;

    private static readonly FieldInfo s_bitsField;

​

    static BigIntegerExtensions()

    {

        s_signField = typeof(BigInteger)

            .GetField("_sign", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new Exception("Could not find BigInteger._sign field");

​

        s_bitsField = typeof(BigInteger)

            .GetField("_bits", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new Exception("Could not find BigInteger._bits field");

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static uint ToUInt32Truncate(this BigInteger value)

    {

        if (value.GetBitLength() < 256)

        {

            return BitConverter.ToUInt32(value.ToByteArray().AsSpan(0, 4));

        }

​

        uint[]? magnitude = (uint[]?)s_bitsField.GetValue(value);

        int sign = (int)s_signField.GetValue(value)!;

​

        if (magnitude is null)

        {

            if (sign >= 0)

                return (uint)sign;

​

            unchecked

            {

                uint absSign = (uint)(-sign);

                return (uint)(~absSign + 1);

            }

        }

​

        uint lowWord = magnitude.Length > 0 ? magnitude[0] : 0u;

        return sign > 0 ? lowWord : unchecked((uint)(~lowWord + 1));

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static int ToInt32Truncate(this BigInteger value)

    {

        uint u = value.ToUInt32Truncate();

        return unchecked((int)u);

    }

}

​

public static class BigIntegerCompiledAccess

{

    public static readonly Func<BigInteger, int> GetSign;

    public static readonly Func<BigInteger, uint[]?> GetBits;

​

    static BigIntegerCompiledAccess()

    {

        // Expression: (BigInteger x) => x._sign

        var param = Expression.Parameter(typeof(BigInteger), "x");

​

        var signField = typeof(BigInteger)

            .GetField("_sign", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new InvalidOperationException("Field '_sign' not found");

​

        var bitsField = typeof(BigInteger)

            .GetField("_bits", BindingFlags.NonPublic | BindingFlags.Instance)

            ?? throw new InvalidOperationException("Field '_bits' not found");

​

        GetSign = Expression.Lambda<Func<BigInteger, int>>(

            Expression.Field(param, signField), param).Compile();

​

        GetBits = Expression.Lambda<Func<BigInteger, uint[]?>>(

            Expression.Field(param, bitsField), param).Compile();

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static uint ToUInt32TruncateCompiled(this BigInteger value)

    {

        if (value.IsZero) return 0u;

​

        int sign = BigIntegerCompiledAccess.GetSign(value);

        uint[]? magnitude = BigIntegerCompiledAccess.GetBits(value);

​

        if (magnitude is null)

        {

            if (sign >= 0) return (uint)sign;

            unchecked

            {

                uint absSign = (uint)(-sign);

                return (uint)(~absSign + 1);

            }

        }

​

        uint lowWord = magnitude.Length > 0 ? magnitude[0] : 0u;

        return sign > 0 ? lowWord : unchecked((uint)(~lowWord + 1));

    }

​

    [MethodImpl(MethodImplOptions.AggressiveInlining)]

    public static int ToInt32TruncateCompiled(this BigInteger value)

    {

        return unchecked((int)value.ToUInt32TruncateCompiled());

    }

}