Clean up

Author: EgorBo

src/libraries/Common/src/System/IO/Hashing/NonCryptographicHashAlgorithm.cs

@@ -15,7 +15,7 @@ namespace System.IO.Hashing
     ///   Represents a non-cryptographic hash algorithm.
     /// </summary>
 #if SYSTEM_PRIVATE_CORELIB
-    #pragma warning disable CA1512
+#pragma warning disable CA1512
     internal
 #else
     public

src/libraries/Common/src/System/IO/Hashing/XxHash3.cs

@@ -16,13 +16,12 @@ namespace System.IO.Hashing
     /// For methods that persist the computed numerical hash value as bytes,
     /// the value is written in the Big Endian byte order.
     /// </remarks>
-#if SYSTEM_PRIVATE_CORELIB
-#pragma warning disable CA1512
-    internal
-#else
 #if NET
     [SkipLocalsInit]
 #endif
+#if SYSTEM_PRIVATE_CORELIB
+    internal
+#else
     public
 #endif
     sealed unsafe class XxHash3 : NonCryptographicHashAlgorithm

src/libraries/Common/src/System/IO/Hashing/XxHash64.State.cs

@@ -12,7 +12,7 @@
 
 namespace System.IO.Hashing
 {
-    #if SYSTEM_PRIVATE_CORELIB
+#if SYSTEM_PRIVATE_CORELIB
     internal
 #else
     public

src/libraries/Common/src/System/IO/Hashing/XxHash64.cs

@@ -16,7 +16,6 @@ namespace System.IO.Hashing
     /// the value is written in the Big Endian byte order.
     /// </remarks>
 #if SYSTEM_PRIVATE_CORELIB
-    #pragma warning disable CA1512
     internal
 #else
     public

src/libraries/System.Private.CoreLib/src/System/String.Comparison.cs

@@ -1,12 +1,15 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#if !MONO && (TARGET_AMD64 || TARGET_ARM64)
+#define USE_XXHASH3
+#endif
+
 using System.Buffers;
 using System.Buffers.Binary;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
-using System.IO.Hashing;
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -813,6 +816,16 @@ internal static int GetHashCodeOrdinalIgnoreCase(ReadOnlySpan<char> value)
             return Marvin.ComputeHash32OrdinalIgnoreCase(ref MemoryMarshal.GetReference(value), value.Length /* in chars, not bytes */, (uint)seed, (uint)(seed >> 32));
         }
 
+#if USE_XXHASH3
+#if TARGET_AMD64
+        private const int XxHash3Threshold = 64;
+#else
+        // XxHash3 is less efficient on ARM64 due to the lack of 256/512-bit vectors
+        // We should revisit this if we start using SVE in the hash implementation.
+        private const int XxHash3Threshold = 128;
+#endif
+#endif
+
         // Important GetNonRandomizedHashCode{OrdinalIgnoreCase} notes:
         //
         // Use if and only if 'Denial of Service' attacks are not a concern (i.e. never used for free-form user input),
@@ -832,12 +845,13 @@ internal unsafe int GetNonRandomizedHashCode()
         {
             fixed (char* src = &_firstChar)
             {
-                // TODO-PR: find optimal threshold
-                if (_stringLength >= 64)
+#if USE_XXHASH3
+                if (_stringLength >= XxHash3Threshold)
                 {
                     uint byteLength = (uint)_stringLength * 2; // never overflows
-                    return unchecked((int)XxHash3.NonRandomizedHashToUInt64((byte*)src, byteLength));
+                    return unchecked((int)System.IO.Hashing.XxHash3.NonRandomizedHashToUInt64((byte*)src, byteLength));
                 }
+#endif
 
                 Debug.Assert(src[Length] == '\0', "src[Length] == '\\0'");
                 Debug.Assert(((int)src) % 4 == 0, "Managed string should start at 4 bytes boundary");
@@ -879,6 +893,14 @@ internal static unsafe int GetNonRandomizedHashCode(ReadOnlySpan<char> span)
                 switch (length)
                 {
                     default:
+#if USE_XXHASH3
+                        if (length >= XxHash3Threshold)
+                        {
+                            uint byteLength = (uint)length * 2; // never overflows
+                            return unchecked((int)System.IO.Hashing.XxHash3.NonRandomizedHashToUInt64((byte*)src, byteLength));
+                        }
+#endif
+
                         do
                         {
                             length -= 4;