asp.net三层架构是哪三层（在.Net7中ArraySpan的IndexOf性能优化）

前一段时间.Net源码有关Array下IndexOf性能优化,说是Array,还是跟Span有关,主要是Array下IndexOf和Span下Contains在值类型(int和long),会调用SpanHelp.T.cs文件中的IndexOfValueType方法.这次是使用指令集(向量)优化.

1. 具体的issue: Vectorize SpanHelpers<T>.IndexOf (#60974)

using System; using BenchmarkDotNet.Attributes; using BenchmarkDotNet.Order; namespace CSharpBenchmarks.SpanTest { [MemoryDiagnoser] [DisassemblyDiagnoser(printSource: true)] [Orderer(SummaryOrderPolicy.FastestToSlowest)] public class IndexOfTest { public byte[] bytes = new byte[] { 0, 0, 0, 0, 71, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 71, 0, 1, 0, 0, 0, 0, 1, 1, 0, 2, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0 }; public byte[] searchBytes = new byte[] { 0, 1, 0, 0 }; [Params(1024, 2048)] public int Times { get; set; } [Benchmark] public int SpanIndexOf() { int sum = 0; for (int i = 0; i < Times; i ) { sum = bytes.AsSpan().IndexOf(searchBytes); } return sum; } [Benchmark] public int SpanLastIndexOf() { int sum = 0; for (int i = 0; i < Times; i ) { sum = bytes.AsSpan().LastIndexOf(searchBytes); } return sum; } } }

测试在.Net 7中Array和Span的IndexOf方法性能改进

从测试结果得出:IndexOf在.Net 7上相对.Net 6提升了71%,LastIndexOf在.Net 7上相对.Net 6提升36%(提升没那么多).因为是指令集优化,生成的汇编代码比较多,这里就就不贴了.

我们可以学习IndexOfValueType源码:

internal static unsafe int IndexOfValueType<T>(ref T searchSpace, T value, int length) where T : struct, IEquatable<T> { Debug.Assert(length >= 0); nint index = 0; // Use nint for arithmetic to avoid unnecessary 64->32->64 truncations if (Vector.IsHardwareAccelerated && Vector<T>.IsTypeSupported && (Vector<T>.Count * 2) <= length) { Vector<T> valueVector = new Vector<T>(value); Vector<T> compareVector = default; Vector<T> matchVector = default; if ((uint)length % (uint)Vector<T>.Count != 0) { // Number of elements is not a multiple of Vector<T>.Count, so do one // check and shift only enough for the remaining set to be a multiple // of Vector<T>.Count. compareVector = Unsafe.As<T, Vector<T>>(ref Unsafe.Add(ref searchSpace, index)); matchVector = Vector.Equals(valueVector, compareVector); if (matchVector != Vector<T>.Zero) { goto VectorMatch; } index = length % Vector<T>.Count; length -= length % Vector<T>.Count; } while (length > 0) { compareVector = Unsafe.As<T, Vector<T>>(ref Unsafe.Add(ref searchSpace, index)); matchVector = Vector.Equals(valueVector, compareVector); if (matchVector != Vector<T>.Zero) { goto VectorMatch; } index = Vector<T>.Count; length -= Vector<T>.Count; } goto NotFound; VectorMatch: for (int i = 0; i < Vector<T>.Count; i ) if (compareVector[i].Equals(value)) return (int)(index i); } while (length >= 8) { if (value.Equals(Unsafe.Add(ref searchSpace, index))) goto Found; if (value.Equals(Unsafe.Add(ref searchSpace, index 1))) goto Found1; if (value.Equals(Unsafe.Add(ref searchSpace, index 2))) goto Found2; if (value.Equals(Unsafe.Add(ref searchSpace, index 3))) goto Found3; if (value.Equals(Unsafe.Add(ref searchSpace, index 4))) goto Found4; if (value.Equals(Unsafe.Add(ref searchSpace, index 5))) goto Found5; if (value.Equals(Unsafe.Add(ref searchSpace, index 6))) goto Found6; if (value.Equals(Unsafe.Add(ref searchSpace, index 7))) goto Found7; length -= 8; index = 8; } while (length >= 4) { if (value.Equals(Unsafe.Add(ref searchSpace, index))) goto Found; if (value.Equals(Unsafe.Add(ref searchSpace, index 1))) goto Found1; if (value.Equals(Unsafe.Add(ref searchSpace, index 2))) goto Found2; if (value.Equals(Unsafe.Add(ref searchSpace, index 3))) goto Found3; length -= 4; index = 4; } while (length > 0) { if (value.Equals(Unsafe.Add(ref searchSpace, index))) goto Found; index = 1; length--; } NotFound: return -1; Found: // Workaround for https://github.com/dotnet/runtime/issues/8795 return (int)index; Found1: return (int)(index 1); Found2: return (int)(index 2); Found3: return (int)(index 3); Found4: return (int)(index 4); Found5: return (int)(index 5); Found6: return (int)(index 6); Found7: return (int)(index 7); }

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