在 c# 中使用 SSE 4.2 crc32 算法？ 可能吗？

Question

I have to calculate crc32 on a lot of files, and also huge files (several GB). I tried several algo found on the web like Damieng or this one , and it works, but it is slow (more than 1 min). I found this benchmark on various crc32 algo and found that sse 4.2 have hardware accelerated crc32 method.

I didn't find anywhere c# code sample to use SSE crc32 code.

1 - Is it possible?

2 - How can I detect if the current cpu is SSE4.2-enabled? (to switch the crc32 method)

(please code sample if possible)

Answer 1

Nowadays we've been spoiled with the System.Runtime.Intrinsics.X86 namespace available in .NET Core 3.0. Here's the full implementation of the CRC32-C algorithm using SSE 4.2:

using System;
using System.Runtime.Intrinsics.X86;
using System.Security.Cryptography;

/// <summary>
/// The hardware implementation of the CRC32-C polynomial 
/// implemented on Intel CPUs supporting SSE4.2.
/// </summary>
public class Crc32HardwareAlgorithm : HashAlgorithm
{
    /// <summary>
    /// the current CRC value, bit-flipped
    /// </summary>
    private uint _crc;

    /// <summary>
    /// We can further optimize the algorithm when X64 is available.
    /// </summary>
    private bool _x64Available;

    /// <summary>
    /// Default constructor
    /// </summary>
    public Crc32HardwareAlgorithm()
    {
        if (!Sse42.IsSupported)
        {
            throw new NotSupportedException("SSE4.2 is not supported");
        }

        _x64Available = Sse42.X64.IsSupported;

        // The size, in bits, of the computed hash code.
        this.HashSizeValue = 32;
        this.Reset();
    }

    /// <summary>When overridden in a derived class, routes data written to the object into the hash algorithm for computing the hash.</summary>
    /// <param name="array">The input to compute the hash code for.</param>
    /// <param name="ibStart">The offset into the byte array from which to begin using data.</param>
    /// <param name="cbSize">The number of bytes in the byte array to use as data.</param>
    protected override void HashCore(byte[] array, int ibStart, int cbSize)
    {
        if (_x64Available)
        {
            while (cbSize >= 8)
            {
                _crc = (uint)Sse42.X64.Crc32(_crc, BitConverter.ToUInt64(array, ibStart));
                ibStart += 8;
                cbSize -= 8;
            }
        }

        while (cbSize > 0)
        {
            _crc = Sse42.Crc32(_crc, array[ibStart]);
            ibStart++;
            cbSize--;
        }
    }

    /// <summary>When overridden in a derived class, finalizes the hash computation after the last data is processed by the cryptographic stream object.</summary>
    /// <returns>The computed hash code.</returns>
    protected override byte[] HashFinal()
    {
        uint outputCrcValue = ~_crc;

        return BitConverter.GetBytes(outputCrcValue);
    }

    /// <summary>Initializes an implementation of the <see cref="T:System.Security.Cryptography.HashAlgorithm"></see> class.</summary>
    public override void Initialize()
    {
        this.Reset();
    }

    private void Reset()
    {
        _crc = uint.MaxValue;
    }
}

Answer 2

I believe Mono allows access to CPU instructions via the Mono.Simd namespace:

http://tirania.org/blog/archive/2008/Nov-03.html

Stackoverflow related question:

Using SSE in c# is it possible?

The Mono code is open source. It looks like you can't just add this to a .NET project to get the benefit though as it appears to need the Mono runtime:

Calling mono c# code from Microsoft .net?

That said, it will work, but it will be software emulated.