Speedup SpanHelpers.IndexOf{Any}(byte, ...) (dotnet/coreclr#22118)

* Speedup SpanHelpers.IndexOf(byte) * 128 * 2 alignment * Move TrailingZeroCountFallback to common SpanHelpers So it can be used by other types than byte * Speedup SpanHelpers.IndexOfAny(byte, ...) * Indent for support flags * More helpers, constency in local names/formatting, feedback * Skip bounds check in software fallback Signed-off-by: dotnet-bot <[email protected]>
Dotnet-GitSync-Bot · Jan 24, 2019 · 2536d86 · 2536d86
1 parent 7d3dc51
commit 2536d86
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diff --git a/netcore/System.Private.CoreLib/shared/System.Private.CoreLib.Shared.projitems b/netcore/System.Private.CoreLib/shared/System.Private.CoreLib.Shared.projitems
@@ -47,6 +47,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\AttributeUsageAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\BadImageFormatException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\BitConverter.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\BitOps.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Boolean.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Buffers\ArrayPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Buffers\ArrayPoolEventSource.cs" />

diff --git a/netcore/System.Private.CoreLib/shared/System/BitOps.cs b/netcore/System.Private.CoreLib/shared/System/BitOps.cs
@@ -0,0 +1,38 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics.X86;
+
+using Internal.Runtime.CompilerServices;
+
+namespace System
+{
+    internal static class BitOps
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int TrailingZeroCount(int matches)
+        {
+            if (Bmi1.IsSupported)
+            {
+                return (int)Bmi1.TrailingZeroCount((uint)matches);
+            }
+            else // Software fallback
+            {
+                // https://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
+                // uint.MaxValue >> 27 is always in range [0 - 31] so we use Unsafe.AddByteOffset to avoid bounds check
+                return Unsafe.AddByteOffset(
+                    ref MemoryMarshal.GetReference(TrailingCountMultiplyDeBruijn),
+                    ((uint)((matches & -matches) * 0x077CB531U)) >> 27);
+            }
+        }
+
+        private static ReadOnlySpan<byte> TrailingCountMultiplyDeBruijn => new byte[32]
+        {
+            0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
+            31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
+        };
+    }
+}