// Licensed to the .NET Foundation under one or more agreements. // The .NET Foundation licenses this file to you under the MIT license. using System.Diagnostics; using System.Numerics; using System.Runtime.CompilerServices; using System.Runtime.InteropServices; using System.Runtime.Intrinsics; using System.Runtime.Intrinsics.Arm; using System.Runtime.Intrinsics.Wasm; using System.Runtime.Intrinsics.X86; namespace System.Buffers { /// <summary> /// Provides a set of initialization methods for instances of the <see cref="SearchValues{T}"/> class. /// </summary> /// <remarks> /// SearchValues are optimized for situations where the same set of values is frequently used for searching at runtime. /// </remarks> public static class SearchValues { /// <summary> /// Creates an optimized representation of <paramref name="values"/> used for efficient searching. /// </summary> /// <param name="values">The set of values.</param> /// <returns>The optimized representation of <paramref name="values"/> used for efficient searching.</returns> public static SearchValues<byte> Create(params ReadOnlySpan<byte> values) { if (values.IsEmpty) { return new EmptySearchValues<byte>(); } if (values.Length == 1) { return new Any1SearchValues<byte, byte>(values); } // RangeByteSearchValues is slower than SingleByteSearchValues, but faster than Any2ByteSearchValues if (TryGetSingleRange(values, out byte minInclusive, out byte maxInclusive)) { return new RangeByteSearchValues(minInclusive, maxInclusive); } // Depending on the hardware, UniqueLowNibble can be faster than even range or 2 values. // It's currently consistently faster than 4/5 values on all tested platforms (Arm, Avx2, Avx512). if (values.Length >= 4 && IndexOfAnyAsciiSearcher.CanUseUniqueLowNibbleSearch(values, maxInclusive)) { return new AsciiByteSearchValues<TrueConst>(values); } if (values.Length <= 5) { Debug.Assert(values.Length is 2 or 3 or 4 or 5); return values.Length switch { 2 => new Any2SearchValues<byte, byte>(values), 3 => new Any3SearchValues<byte, byte>(values), 4 => new Any4SearchValues<byte, byte>(values), _ => new Any5SearchValues<byte, byte>(values), }; } if (IndexOfAnyAsciiSearcher.IsVectorizationSupported && maxInclusive < 128) { return new AsciiByteSearchValues<FalseConst>(values); } return new AnyByteSearchValues(values); } /// <summary> /// Creates an optimized representation of <paramref name="values"/> used for efficient searching. /// </summary> /// <param name="values">The set of values.</param> /// <returns>The optimized representation of <paramref name="values"/> used for efficient searching.</returns> public static unsafe SearchValues<char> Create(params ReadOnlySpan<char> values) { if (values.IsEmpty) { return new EmptySearchValues<char>(); } // Vector128<char> isn't valid. Treat the values as shorts instead. ReadOnlySpan<short> shortValues = MemoryMarshal.Cast<char, short>(values); if (values.Length == 1) { char value = values[0]; return PackedSpanHelpers.PackedIndexOfIsSupported && PackedSpanHelpers.CanUsePackedIndexOf(value) ? new Any1CharPackedSearchValues(value) : new Any1SearchValues<char, short>(shortValues); } // RangeCharSearchValues is slower than SingleCharSearchValues, but faster than Any2CharSearchValues if (TryGetSingleRange(values, out char minInclusive, out char maxInclusive)) { return PackedSpanHelpers.PackedIndexOfIsSupported && PackedSpanHelpers.CanUsePackedIndexOf(minInclusive) && PackedSpanHelpers.CanUsePackedIndexOf(maxInclusive) ? new RangeCharSearchValues<TrueConst>(minInclusive, maxInclusive) : new RangeCharSearchValues<FalseConst>(minInclusive, maxInclusive); } if (values.Length == 2) { char value0 = values[0]; char value1 = values[1]; if (PackedSpanHelpers.PackedIndexOfIsSupported && PackedSpanHelpers.CanUsePackedIndexOf(value0) && PackedSpanHelpers.CanUsePackedIndexOf(value1)) { // If the two values are the same ASCII letter with both cases, we can use an approach that // reduces the number of comparisons by masking off the bit that differs between lower and upper case (0x20). // While this most commonly applies to ASCII letters, it also works for other values that differ by 0x20 (e.g. "[{" => "{"). return (value0 ^ value1) == 0x20 ? new Any1CharPackedIgnoreCaseSearchValues((char)Math.Max(value0, value1)) : new Any2CharPackedSearchValues(value0, value1); } return new Any2SearchValues<char, short>(shortValues); } if (values.Length == 3) { char value0 = values[0]; char value1 = values[1]; char value2 = values[2]; return PackedSpanHelpers.PackedIndexOfIsSupported && PackedSpanHelpers.CanUsePackedIndexOf(value0) && PackedSpanHelpers.CanUsePackedIndexOf(value1) && PackedSpanHelpers.CanUsePackedIndexOf(value2) ? new Any3CharPackedSearchValues(value0, value1, value2) : new Any3SearchValues<char, short>(shortValues); } // If the values are sets of 2 ASCII letters with both cases, we can use an approach that // reduces the number of comparisons by masking off the bit that differs between lower and upper case (0x20). // While this most commonly applies to ASCII letters, it also works for other values that differ by 0x20 (e.g. "[]{}" => "{}"). if (IndexOfAnyAsciiSearcher.IsVectorizationSupported && PackedSpanHelpers.PackedIndexOfIsSupported && maxInclusive < 128 && values.Length == 4 && minInclusive > 0) { Span<char> copy = ['\0', '\0', '\0', '\0']; values.CopyTo(copy); copy.Sort(); if ((copy[0] ^ copy[2]) == 0x20 && (copy[1] ^ copy[3]) == 0x20) { // We pick the higher two values (with the 0x20 bit set). "AaBb" => 'a', 'b' return new Any2CharPackedIgnoreCaseSearchValues(copy[2], copy[3]); } } // Depending on the hardware, UniqueLowNibble can be faster than most implementations we currently prefer above. // It's currently consistently faster than 4/5 values or Ascii on all tested platforms (Arm, Avx2, Avx512). if (IndexOfAnyAsciiSearcher.CanUseUniqueLowNibbleSearch(values, maxInclusive)) { return (Ssse3.IsSupported || PackedSimd.IsSupported) && minInclusive == 0 ? new AsciiCharSearchValues<IndexOfAnyAsciiSearcher.Ssse3AndWasmHandleZeroInNeedle, TrueConst>(values) : new AsciiCharSearchValues<IndexOfAnyAsciiSearcher.Default, TrueConst>(values); } // IndexOfAnyAsciiSearcher for chars is slower than Any3CharSearchValues, but faster than Any4SearchValues if (IndexOfAnyAsciiSearcher.IsVectorizationSupported && maxInclusive < 128) { return (Ssse3.IsSupported || PackedSimd.IsSupported) && minInclusive == 0 ? new AsciiCharSearchValues<IndexOfAnyAsciiSearcher.Ssse3AndWasmHandleZeroInNeedle, FalseConst>(values) : new AsciiCharSearchValues<IndexOfAnyAsciiSearcher.Default, FalseConst>(values); } if (values.Length == 4) { return new Any4SearchValues<char, short>(shortValues); } if (values.Length == 5) { return new Any5SearchValues<char, short>(shortValues); } if (IndexOfAnyAsciiSearcher.IsVectorizationSupported && minInclusive < 128) { // If we have both ASCII and non-ASCII characters, use an implementation that // does an optimistic ASCII fast-path and then falls back to the ProbabilisticMap. return (Ssse3.IsSupported || PackedSimd.IsSupported) && minInclusive == 0 ? new ProbabilisticWithAsciiCharSearchValues<IndexOfAnyAsciiSearcher.Ssse3AndWasmHandleZeroInNeedle>(values, maxInclusive) : new ProbabilisticWithAsciiCharSearchValues<IndexOfAnyAsciiSearcher.Default>(values, maxInclusive); } if (ShouldUseProbabilisticMap(values.Length, maxInclusive)) { return new ProbabilisticCharSearchValues(values, maxInclusive); } // This will also match ASCII values when IndexOfAnyAsciiSearcher is not supported. return new BitmapCharSearchValues(values, maxInclusive); static bool ShouldUseProbabilisticMap(int valuesLength, int maxInclusive) { // *Rough estimates*. The current implementation uses 256 bits for the bloom filter. // If the implementation is vectorized we can get away with a decent false positive rate. const int MaxValuesForProbabilisticMap = 256; if (valuesLength > MaxValuesForProbabilisticMap) { // If the number of values is too high, we won't see any benefits from the 'probabilistic' part. return false; } if (Sse41.IsSupported || AdvSimd.Arm64.IsSupported) { // If the probabilistic map is vectorized, we prefer it. return true; } // The probabilistic map is more memory efficient for spare sets, while the bitmap is more efficient for dense sets. int bitmapFootprintBytesEstimate = 64 + (maxInclusive / 8); int probabilisticFootprintBytesEstimate = 128 + (valuesLength * 4); // The bitmap is a bit faster than the perfect hash checks employed by the probabilistic map. // Sacrifice some memory usage for faster lookups. const int AcceptableSizeMultiplier = 2; return AcceptableSizeMultiplier * probabilisticFootprintBytesEstimate < bitmapFootprintBytesEstimate; } } /// <summary> /// Creates an optimized representation of <paramref name="values"/> used for efficient searching. /// </summary> /// <param name="values">The set of values.</param> /// <param name="comparisonType">Specifies whether to use <see cref="StringComparison.Ordinal"/> or <see cref="StringComparison.OrdinalIgnoreCase"/> search semantics.</param> /// <returns>The optimized representation of <paramref name="values"/> used for efficient searching.</returns> /// <remarks>Only <see cref="StringComparison.Ordinal"/> or <see cref="StringComparison.OrdinalIgnoreCase"/> may be used.</remarks> public static SearchValues<string> Create(ReadOnlySpan<string> values, StringComparison comparisonType) { if (comparisonType is not (StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase)) { throw new ArgumentException(SR.Argument_SearchValues_UnsupportedStringComparison, nameof(comparisonType)); } return StringSearchValues.Create(values, ignoreCase: comparisonType == StringComparison.OrdinalIgnoreCase); } private static bool TryGetSingleRange<T>(ReadOnlySpan<T> values, out T minInclusive, out T maxInclusive) where T : struct, INumber<T> { minInclusive = values.Min(); maxInclusive = values.Max(); uint range = uint.CreateChecked(maxInclusive - minInclusive) + 1; if (range > values.Length) { return false; } Span<bool> seenValues = range <= 256 ? stackalloc bool[256] : new bool[range]; seenValues = seenValues.Slice(0, (int)range); seenValues.Clear(); foreach (T value in values) { int offset = int.CreateChecked(value - minInclusive); seenValues[offset] = true; } if (seenValues.Contains(false)) { return false; } return true; } internal interface IRuntimeConst { static abstract bool Value { get; } } internal readonly struct TrueConst : IRuntimeConst { public static bool Value => true; } internal readonly struct FalseConst : IRuntimeConst { public static bool Value => false; } /// <summary> /// Same as <see cref="Vector128.ShuffleNative(Vector128{byte}, Vector128{byte})"/>, except that we guarantee that <see cref="Ssse3.Shuffle(Vector128{byte}, Vector128{byte})"/> is used when available. /// Some logic in <see cref="SearchValues"/> relies on this exact behavior (implicit AND 0xF, and zeroing when the high bit is set). /// </summary> [MethodImpl(MethodImplOptions.AggressiveInlining)] [CompExactlyDependsOn(typeof(Ssse3))] [CompHasFallback] internal static Vector128<byte> ShuffleNativeModified(Vector128<byte> vector, Vector128<byte> indices) { if (Ssse3.IsSupported) { return Ssse3.Shuffle(vector, indices); } return Vector128.Shuffle(vector, indices); } } }