56 lines
1.8 KiB
C#
56 lines
1.8 KiB
C#
namespace ActivityPub.Utils;
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/// <summary>
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/// Helper class for converting numbers to and from Base36 strings
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/// https://stackoverflow.com/a/35004409
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/// </summary>
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public class Base36
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{
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private static readonly char[] BaseChars =
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"0123456789abcdefghijklmnopqrstuvwxyz".ToCharArray();
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private static readonly Dictionary<char, int> CharValues = BaseChars
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.Select((c, i) => new { Char = c, Index = i })
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.ToDictionary(c => c.Char, c => c.Index);
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/// <summary>
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/// Convert a long to a Base36 string
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/// </summary>
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/// <param name="value">The number to convert</param>
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/// <returns>A string representing the number in Base36</returns>
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public static string ToString(long value)
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{
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long targetBase = BaseChars.Length;
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// Determine exact number of characters to use.
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char[] buffer = new char[Math.Max(
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(int)Math.Ceiling(Math.Log(value + 1, targetBase)), 1)];
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var i = buffer.Length;
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do
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{
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buffer[--i] = BaseChars[value % targetBase];
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value = value / targetBase;
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}
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while (value > 0);
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return new string(buffer, i, buffer.Length - i);
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}
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/// <summary>
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/// Converts a Base64 string back into a number
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/// </summary>
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/// <param name="number">The string to convert</param>
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/// <returns>The number resulting from converting the string</returns>
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public static long FromString(string number)
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{
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char[] chrs = number.ToLower().ToCharArray();
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int m = chrs.Length - 1;
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int n = BaseChars.Length, x;
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long result = 0;
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for (int i = 0; i < chrs.Length; i++)
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{
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x = CharValues[chrs[i]];
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result += x * (long)Math.Pow(n, m--);
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}
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return result;
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}
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}
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