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Make decode even faster
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parent
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commit
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@ -1,5 +1,5 @@
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using System;
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using System.Globalization;
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using System.Diagnostics.CodeAnalysis;
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namespace MediaBrowser.Common
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{
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@ -11,6 +11,23 @@ namespace MediaBrowser.Common
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internal const string HexCharsLower = "0123456789abcdef";
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internal const string HexCharsUpper = "0123456789ABCDEF";
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internal const int LastHexSymbol = 0x66; // 102: f
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/// <summary>
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/// Map from an ASCII char to its hex value shifted,
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/// e.g. <c>b</c> -> 11. 0xFF means it's not a hex symbol.
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/// </summary>
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/// <value></value>
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internal static ReadOnlySpan<byte> HexLookup => new byte[] {
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
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};
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/// <summary>
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/// Encodes <c>bytes</c> as a hex string.
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/// </summary>
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@ -41,17 +58,37 @@ namespace MediaBrowser.Common
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/// <returns>The decoded bytes.</returns>
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public static byte[] Decode(ReadOnlySpan<char> str)
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{
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byte[] bytes = new byte[str.Length / 2];
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int j = 0;
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for (int i = 0; i < str.Length; i += 2)
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if (str.Length == 0)
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{
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bytes[j++] = byte.Parse(
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str.Slice(i, 2),
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NumberStyles.HexNumber,
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CultureInfo.InvariantCulture);
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return Array.Empty<byte>();
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}
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var unHex = HexLookup;
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int byteLen = str.Length / 2;
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byte[] bytes = new byte[byteLen];
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int i = 0;
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for (int j = 0; j < byteLen; j++)
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{
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byte a;
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byte b;
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if (str[i] > LastHexSymbol
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|| (a = unHex[str[i++]]) == 0xFF
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|| str[i] > LastHexSymbol
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|| (b = unHex[str[i++]]) == 0xFF)
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{
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ThrowArgumentException(nameof(str));
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break; // Unreachable
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}
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bytes[j] = (byte)((a << 4) | b);
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}
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return bytes;
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}
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[DoesNotReturn]
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private static void ThrowArgumentException(string paramName)
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=> throw new ArgumentException("Character is not a hex symbol.", paramName);
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}
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}
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@ -9,10 +9,13 @@ namespace Jellyfin.Common.Benches
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[MemoryDiagnoser]
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public class HexDecodeBenches
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{
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private const int N = 1000000;
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private readonly string data;
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[Params(0, 10, 100, 1000, 10000, 1000000)]
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public int N { get; set; }
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public HexDecodeBenches()
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private string data;
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[GlobalSetup]
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public void GlobalSetup()
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{
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var tmp = new byte[N];
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new Random(42).NextBytes(tmp);
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