jellyfin-server/MediaBrowser.Common/Hex.cs
2019-11-01 17:52:29 +01:00

95 lines
3.4 KiB
C#

using System;
using System.Diagnostics.CodeAnalysis;
namespace MediaBrowser.Common
{
/// <summary>
/// Encoding and decoding hex strings.
/// </summary>
public static class Hex
{
internal const string HexCharsLower = "0123456789abcdef";
internal const string HexCharsUpper = "0123456789ABCDEF";
internal const int LastHexSymbol = 0x66; // 102: f
/// <summary>
/// Map from an ASCII char to its hex value shifted,
/// e.g. <c>b</c> -> 11. 0xFF means it's not a hex symbol.
/// </summary>
/// <value></value>
internal static ReadOnlySpan<byte> HexLookup => new byte[] {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
};
/// <summary>
/// Encodes <c>bytes</c> as a hex string.
/// </summary>
/// <param name="bytes"></param>
/// <param name="lowercase"></param>
/// <returns><c>bytes</c> as a hex string.</returns>
public static string Encode(ReadOnlySpan<byte> bytes, bool lowercase = true)
{
var hexChars = lowercase ? HexCharsLower : HexCharsUpper;
// TODO: use string.Create when it's supports spans
// Ref: https://github.com/dotnet/corefx/issues/29120
char[] s = new char[bytes.Length * 2];
int j = 0;
for (int i = 0; i < bytes.Length; i++)
{
s[j++] = hexChars[bytes[i] >> 4];
s[j++] = hexChars[bytes[i] & 0x0f];
}
return new string(s);
}
/// <summary>
/// Decodes a hex string into bytes.
/// </summary>
/// <param name="str">The <see cref="string" />.</param>
/// <returns>The decoded bytes.</returns>
public static byte[] Decode(ReadOnlySpan<char> str)
{
if (str.Length == 0)
{
return Array.Empty<byte>();
}
var unHex = HexLookup;
int byteLen = str.Length / 2;
byte[] bytes = new byte[byteLen];
int i = 0;
for (int j = 0; j < byteLen; j++)
{
byte a;
byte b;
if (str[i] > LastHexSymbol
|| (a = unHex[str[i++]]) == 0xFF
|| str[i] > LastHexSymbol
|| (b = unHex[str[i++]]) == 0xFF)
{
ThrowArgumentException(nameof(str));
break; // Unreachable
}
bytes[j] = (byte)((a * 16) | b);
}
return bytes;
}
[DoesNotReturn]
private static void ThrowArgumentException(string paramName)
=> throw new ArgumentException("Character is not a hex symbol.", paramName);
}
}