41 lines
1.1 KiB
C#
41 lines
1.1 KiB
C#
using System.Runtime.InteropServices;
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using System.Security.Cryptography;
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namespace Just.Core;
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public enum GuidV8Entropy { Strong, Weak }
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public static class GuidV8
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{
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[Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static Guid NewGuid(GuidV8Entropy entropy = GuidV8Entropy.Strong) => NewGuid(DateTime.UtcNow, entropy);
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[Pure]
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public static Guid NewGuid(DateTime dateTime, GuidV8Entropy entropy = GuidV8Entropy.Strong)
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{
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var epoch = dateTime.Subtract(DateTime.UnixEpoch);
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var timestamp = epoch.Ticks / (TimeSpan.TicksPerMillisecond / 10);
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Span<byte> ts = stackalloc byte[8];
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MemoryMarshal.Write(ts, timestamp);
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Span<byte> bytes = stackalloc byte[16];
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ts[0..2].CopyTo(bytes[4..6]);
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ts[2..6].CopyTo(bytes[..4]);
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if (entropy == GuidV8Entropy.Strong)
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{
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RandomNumberGenerator.Fill(bytes[6..]);
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}
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else
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{
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Random.Shared.NextBytes(bytes[6..]);
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}
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bytes[7] = (byte)((bytes[7] & 0x0F) | 0x80);
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return new Guid(bytes);
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}
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}
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