pinvoke for RtlDecompressBufferEx in c#

Win10PrefechDecompress.cs

using System.Runtime.InteropServices;

namespace Prefetch.XpressStream
{
    public class Xpress2
    {
//        const ushort COMPRESSION_FORMAT_LZNT1 = 2;
//        const ushort COMPRESSION_FORMAT_XPRESS = 3;
        const ushort CompressionFormatXpressHuff = 4;

        [DllImport("ntdll.dll")]
        private static extern uint RtlGetCompressionWorkSpaceSize(ushort compressionFormat, ref ulong compressBufferWorkSpaceSize, ref ulong compressFragmentWorkSpaceSize);

        [DllImport("ntdll.dll")]
        private static extern uint RtlDecompressBufferEx(ushort compressionFormat, byte[] uncompressedBuffer, int uncompressedBufferSize, byte[] compressedBuffer, int compressedBufferSize, ref int finalUncompressedSize, byte[] workSpace);

        public static byte[] Decompress(byte[] buffer,ulong decompressedSize)
        {
            // our uncompressed data will go here
            var outBuf = new byte[decompressedSize];
            ulong compressBufferWorkSpaceSize = 0;
            ulong compressFragmentWorkSpaceSize = 0;

            //get the size of what our workspace needs to be
            var ret = RtlGetCompressionWorkSpaceSize(CompressionFormatXpressHuff, ref compressBufferWorkSpaceSize, ref compressFragmentWorkSpaceSize);
            if (ret != 0)
            {
                return null;
            }

            var workSpace = new byte[compressFragmentWorkSpaceSize];
            var dstSize = 0;

            ret = RtlDecompressBufferEx(CompressionFormatXpressHuff, outBuf, outBuf.Length, buffer, buffer.Length, ref dstSize, workSpace);
            if (ret == 0)
            {
                return outBuf;
            }

            return null;
        }
     
    }
}

Also available here

https://github.com/EricZimmerman/Prefetch/blob/master/Prefetch/XpressStream/Xpress2.cs