67 lines
1.7 KiB
C#
67 lines
1.7 KiB
C#
using System.Buffers.Binary;
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namespace Fleet.Core;
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/// <summary>LEB128 变长整数（无符号），以及 zigzag 有符号映射。</summary>
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public static class VarInt
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{
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public const int MaxBytes = 10;
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public static ulong ZigZag(long value) => (ulong)((value << 1) ^ (value >> 63));
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public static long UnZigZag(ulong value) => (long)(value >> 1) ^ -(long)(value & 1);
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public static int Write(Span<byte> destination, ulong value)
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{
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int i = 0;
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while (value >= 0x80)
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{
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destination[i++] = (byte)(value | 0x80);
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value >>= 7;
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}
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destination[i++] = (byte)value;
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return i;
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}
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public static void Write(Stream destination, ulong value)
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{
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Span<byte> buffer = stackalloc byte[MaxBytes];
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int n = Write(buffer, value);
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destination.Write(buffer[..n]);
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}
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/// <summary>读取失败（数据被截断或超过 10 字节）时返回 false。</summary>
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public static bool TryRead(ReadOnlySpan<byte> source, out ulong value, out int consumed)
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{
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value = 0;
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consumed = 0;
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int shift = 0;
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while (consumed < source.Length && consumed < MaxBytes)
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{
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byte b = source[consumed++];
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value |= (ulong)(b & 0x7F) << shift;
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if ((b & 0x80) == 0)
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{
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return true;
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}
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shift += 7;
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}
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return false;
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}
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public static bool TryReadUInt32LittleEndian(ReadOnlySpan<byte> source, out uint value)
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{
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if (source.Length < 4)
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{
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value = 0;
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return false;
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}
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value = BinaryPrimitives.ReadUInt32LittleEndian(source);
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return true;
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}
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}
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