HashCode based on xxHash32 (dotnet#14863)

* HashCode based on xxHash32

Works by maintaining the xxHash32 state variables (v1 -> v4, length) as well as a queue of values that fall outside of the block size (16 bytes/4 ints). The seed is initialized to random bytes.

Further details, unit tests and history: dotnet/corefx#25013

THIRD-PARTY-NOTICES.TXT

@@ -221,3 +221,31 @@ License notice for the Printing Floating-Point Numbers
   3. This notice may not be removed or altered from any source
      distribution.
 ******************************************************************************/
+
+License notice for xxHash
+-------------------------
+
+xxHash Library
+Copyright (c) 2012-2014, Yann Collet
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice, this
+  list of conditions and the following disclaimer in the documentation and/or
+  other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

src/mscorlib/Resources/Strings.resx

@@ -3691,4 +3691,10 @@
   <data name="Memory_OutstandingReferences" xml:space="preserve">
     <value>Release all references before disposing this instance.</value>
   </data>
+  <data name="HashCode_HashCodeNotSupported" xml:space="preserve">
+    <value>HashCode is a mutable struct and should not be compared with other HashCodes. Use ToHashCode to retrieve the computed hash code.</value>
+  </data>
+  <data name="HashCode_EqualityNotSupported" xml:space="preserve">
+    <value>HashCode is a mutable struct and should not be compared with other HashCodes.</value>
+  </data>
 </root>

src/mscorlib/shared/System.Private.CoreLib.Shared.projitems

@@ -159,6 +159,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\UmAlQuraCalendar.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Globalization\UnicodeCategory.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Guid.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\HashCode.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\HResults.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IAsyncResult.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\ICloneable.cs" />