Add XxHash128

src/libraries/System.IO.Hashing/ref/System.IO.Hashing.cs

@@ -59,6 +59,19 @@ protected virtual void GetHashAndResetCore(System.Span<byte> destination) { }
         public bool TryGetCurrentHash(System.Span<byte> destination, out int bytesWritten) { throw null; }
         public bool TryGetHashAndReset(System.Span<byte> destination, out int bytesWritten) { throw null; }
     }
+    public sealed partial class XxHash128 : System.IO.Hashing.NonCryptographicHashAlgorithm
+    {
+        public XxHash128() : base (default(int)) { }
+        public XxHash128(long seed) : base (default(int)) { }
+        public override void Append(System.ReadOnlySpan<byte> source) { }
+        protected override void GetCurrentHashCore(System.Span<byte> destination) { }
+        public static byte[] Hash(byte[] source) { throw null; }
+        public static byte[] Hash(byte[] source, long seed) { throw null; }
+        public static byte[] Hash(System.ReadOnlySpan<byte> source, long seed = (long)0) { throw null; }
+        public static int Hash(System.ReadOnlySpan<byte> source, System.Span<byte> destination, long seed = (long)0) { throw null; }
+        public override void Reset() { }
+        public static bool TryHash(System.ReadOnlySpan<byte> source, System.Span<byte> destination, out int bytesWritten, long seed = (long)0) { throw null; }
+    }
     public sealed partial class XxHash3 : System.IO.Hashing.NonCryptographicHashAlgorithm
     {
         public XxHash3() : base (default(int)) { }

src/libraries/System.IO.Hashing/ref/System.IO.Hashing.csproj

@@ -8,6 +8,10 @@
     <Compile Include="System.IO.Hashing.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <Compile Include="System.IO.Hashing.netcoreapp.cs" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
     <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>

src/libraries/System.IO.Hashing/ref/System.IO.Hashing.netcoreapp.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// ------------------------------------------------------------------------------
+// Changes to this file must follow the https://aka.ms/api-review process.
+// ------------------------------------------------------------------------------
+
+namespace System.IO.Hashing
+{
+    public sealed partial class XxHash128 : System.IO.Hashing.NonCryptographicHashAlgorithm
+    {
+        [System.CLSCompliantAttribute(false)]
+        public System.UInt128 GetCurrentHashAsUInt128() { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static System.UInt128 HashToUInt128(System.ReadOnlySpan<byte> source, long seed = 0) { throw null; }
+    }
+}

src/libraries/System.IO.Hashing/src/System.IO.Hashing.csproj

@@ -15,11 +15,13 @@ System.IO.Hashing.XxHash32</PackageDescription>
     <Compile Include="System\IO\Hashing\Crc32.Table.cs" />
     <Compile Include="System\IO\Hashing\Crc64.cs" />
     <Compile Include="System\IO\Hashing\Crc64.Table.cs" />
+    <Compile Include="System\IO\Hashing\XxHash128.cs" />
     <Compile Include="System\IO\Hashing\XxHash3.cs" />
     <Compile Include="System\IO\Hashing\XxHash32.cs" />
     <Compile Include="System\IO\Hashing\XxHash32.State.cs" />
     <Compile Include="System\IO\Hashing\XxHash64.cs" />
     <Compile Include="System\IO\Hashing\XxHash64.State.cs" />
+    <Compile Include="System\IO\Hashing\XxHashShared.cs" />
     <Compile Include="System\IO\Hashing\NonCryptographicHashAlgorithm.cs" />
     <Compile Include="$(CommonPath)System\Numerics\Crc32ReflectedTable.cs">
       <Link>Common\System\Numerics\Crc32ReflectedTable.cs</Link>