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95 lines
3.5 KiB
95 lines
3.5 KiB
using System;
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using System.Diagnostics.CodeAnalysis;
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namespace MediaBrowser.Common
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{
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/// <summary>
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/// Encoding and decoding hex strings.
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/// </summary>
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public static class Hex
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{
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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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/// Gets a 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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internal static ReadOnlySpan<byte> HexLookup => new byte[]
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{
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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 each element of the specified bytes as its hexadecimal string representation.
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/// </summary>
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/// <param name="bytes">An array of bytes.</param>
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/// <param name="lowercase"><c>true</c> to use lowercase hexadecimal characters; otherwise <c>false</c>.</param>
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/// <returns><c>bytes</c> as a hex string.</returns>
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public static string Encode(ReadOnlySpan<byte> bytes, bool lowercase = true)
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{
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var hexChars = lowercase ? HexCharsLower : HexCharsUpper;
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// TODO: use string.Create when it's supports spans
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// Ref: https://github.com/dotnet/corefx/issues/29120
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char[] s = new char[bytes.Length * 2];
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int j = 0;
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for (int i = 0; i < bytes.Length; i++)
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{
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s[j++] = hexChars[bytes[i] >> 4];
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s[j++] = hexChars[bytes[i] & 0x0f];
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}
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return new string(s);
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}
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/// <summary>
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/// Decodes a hex string into bytes.
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/// </summary>
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/// <param name="str">The <see cref="string" />.</param>
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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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if (str.Length == 0)
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{
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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 * 16) | 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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