Hex <--> Binary

Implementation of API Proposal for dotnet/runtime#17837

API Proposal

namespace System
{
    // NEW type
    [Flags]
    public enum HexFormattingOptions
    {
        None = 0,
        InsertLineBreaks = 1,
        Lowercase = 2
    }

    // NEW methods on EXISTING type
    public static class Convert
    {
        // Decode from chars
        public static byte[] FromHexCharArray(char[] inArray, int offset, int length) => throw null;
        public static bool TryFromHexChars(ReadOnlySpan<char> chars, Span<byte> bytes, out int bytesWritten) => throw null;

        // Decode from strings
        public static byte[] FromHexString(string s) => throw null;
        public static byte[] FromHexString(ReadOnlySpan<char> chars) => throw null;
        public static bool TryFromHexString(string s, Span<byte> bytes, out int bytesWritten) => throw null;

        // Encode to chars
        public static int ToHexCharArray(byte[] inArray, int offsetIn, int length, char[] outArray, int offsetOut, HexFormattingOptions options = default) => throw null;
        public static bool TryToHexChars(ReadOnlySpan<byte> bytes, Span<char> chars, out int charsWritten, HexFormattingOptions options = default) => throw null;

        // Encode to strings
        public static string ToHexString(byte[] inArray, HexFormattingOptions options = default) => throw null;
        public static string ToHexString(byte[] inArray, int offset, int length, HexFormattingOptions options = default) => throw null;
        public static string ToHexString(ReadOnlySpan<byte> bytes, HexFormattingOptions options = default) => throw null;
    }
}

namespace System.Buffers.Text
{
    // NEW type
    public static class Hex
    {
        // Decode
        public static OperationStatus DecodeFromUtf8(ReadOnlySpan<byte> utf8, Span<byte> bytes, out int bytesConsumed, out int bytesWritten, bool isFinalBlock = true) => throw null;
        public static OperationStatus DecodeFromUtf8InPlace(Span<byte> buffer, out int bytesWritten) => throw null;
        
        // Encode
        public static OperationStatus EncodeToUtf8(ReadOnlySpan<byte> bytes, Span<byte> utf8, out int bytesConsumed, out int bytesWritten, bool isFinalBlock = true) => throw null;
        public static OperationStatus EncodeToUtf8InPlace(Span<byte> buffer, int dataLength, out int bytesWritten) => throw null;
    }
}

Performance characteristics

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.207 (2004/?/20H1)
Intel Core i7-9750H CPU 2.60GHz, 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=5.0.100-preview.2.20176.6

Method	Job	DataSize	Mean	Error	StdDev
DecodeUtf16	AVX2	32	18.535 ns	0.0736 ns	0.0615 ns
DecodeUtf16	SSE2	32	28.495 ns	0.5772 ns	0.6647 ns
DecodeUtf16	SSE4.1	32	22.267 ns	0.4771 ns	0.7568 ns
DecodeUtf16	SSSE3	32	22.629 ns	0.1030 ns	0.0860 ns
DecodeUtf16	Scalar	32	36.456 ns	0.2476 ns	0.2316 ns
DecodeUtf16	AVX2	2048	147.228 ns	0.7159 ns	0.5978 ns
DecodeUtf16	SSE2	2048	413.381 ns	1.5861 ns	1.4836 ns
DecodeUtf16	SSE4.1	2048	295.134 ns	5.8257 ns	5.1644 ns
DecodeUtf16	SSSE3	2048	319.053 ns	2.6398 ns	2.3401 ns
DecodeUtf16	Scalar	2048	1,913.189 ns	11.4772 ns	10.7358 ns
DecodeUtf8	AVX2	32	14.601 ns	0.1075 ns	0.0897 ns
DecodeUtf8	SSE2	32	17.503 ns	0.3222 ns	0.3013 ns
DecodeUtf8	SSE4.1	32	13.611 ns	0.0723 ns	0.0641 ns
DecodeUtf8	SSSE3	32	13.762 ns	0.2694 ns	0.2520 ns
DecodeUtf8	Scalar	32	22.227 ns	0.1324 ns	0.1239 ns
DecodeUtf8	AVX2	2048	112.673 ns	0.5130 ns	0.4799 ns
DecodeUtf8	SSE2	2048	371.773 ns	1.4891 ns	1.2434 ns
DecodeUtf8	SSE4.1	2048	247.388 ns	2.9746 ns	2.4839 ns
DecodeUtf8	SSSE3	2048	278.068 ns	1.3503 ns	1.1276 ns
DecodeUtf8	Scalar	2048	1,197.137 ns	4.7857 ns	4.4765 ns
EncodeUtf16	AVX2	32	5.391 ns	0.0482 ns	0.0403 ns
EncodeUtf16	SSE2	32	5.656 ns	0.0372 ns	0.0348 ns
EncodeUtf16	SSE4.1	32	5.553 ns	0.0556 ns	0.0464 ns
EncodeUtf16	SSSE3	32	5.608 ns	0.1093 ns	0.1301 ns
EncodeUtf16	Scalar	32	5.675 ns	0.0409 ns	0.0363 ns
EncodeUtf16	AVX2	2048	5.403 ns	0.0431 ns	0.0337 ns
EncodeUtf16	SSE2	2048	5.500 ns	0.0299 ns	0.0279 ns
EncodeUtf16	SSE4.1	2048	5.300 ns	0.0326 ns	0.0305 ns
EncodeUtf16	SSSE3	2048	5.313 ns	0.0171 ns	0.0151 ns
EncodeUtf16	Scalar	2048	5.372 ns	0.0287 ns	0.0254 ns
EncodeUtf8	AVX2	32	8.222 ns	0.0639 ns	0.0598 ns
EncodeUtf8	SSE2	32	9.779 ns	0.0476 ns	0.0397 ns
EncodeUtf8	SSE4.1	32	7.681 ns	0.0730 ns	0.0683 ns
EncodeUtf8	SSSE3	32	7.763 ns	0.0984 ns	0.0821 ns
EncodeUtf8	Scalar	32	23.286 ns	0.1478 ns	0.1234 ns
EncodeUtf8	AVX2	2048	50.853 ns	0.4674 ns	0.3903 ns
EncodeUtf8	SSE2	2048	98.637 ns	0.5082 ns	0.4505 ns
EncodeUtf8	SSE4.1	2048	65.998 ns	0.3181 ns	0.2820 ns
EncodeUtf8	SSSE3	2048	73.602 ns	0.4883 ns	0.4329 ns
EncodeUtf8	Scalar	2048	487.154 ns	1.9383 ns	1.8131 ns