Joseph Doherty
49 lines
1.7 KiB
C#
49 lines
1.7 KiB
C#
namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus;
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/// <summary>
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/// CRC-16/MODBUS helper: reflected polynomial <c>0xA001</c>, initial value <c>0xFFFF</c>.
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/// On the wire the CRC is appended low byte first, high byte second — <see cref="Append"/>
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/// does that; <see cref="Compute"/> just returns the 16-bit value. Byte-stream-agnostic:
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/// no socket or framing knowledge lives here.
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/// </summary>
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public static class ModbusCrc
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{
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/// <summary>Computes the CRC-16/MODBUS checksum over <paramref name="data"/>.</summary>
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/// <param name="data">The bytes to checksum (e.g. the RTU frame minus the trailing CRC).</param>
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/// <returns>The 16-bit CRC value.</returns>
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public static ushort Compute(ReadOnlySpan<byte> data)
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{
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ushort crc = 0xFFFF;
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foreach (var b in data)
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{
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crc ^= b;
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for (var i = 0; i < 8; i++)
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{
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var carry = (crc & 0x0001) != 0;
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crc >>= 1;
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if (carry)
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{
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crc ^= 0xA001;
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}
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}
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}
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return crc;
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}
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/// <summary>
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/// Returns <paramref name="body"/> with its CRC-16/MODBUS appended, low byte first.
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/// </summary>
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/// <param name="body">The frame body to checksum.</param>
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/// <returns>A new array: <paramref name="body"/> followed by <c>[crc & 0xFF, crc >> 8]</c>.</returns>
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public static byte[] Append(ReadOnlySpan<byte> body)
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{
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var crc = Compute(body);
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var result = new byte[body.Length + 2];
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body.CopyTo(result);
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result[^2] = (byte)(crc & 0xFF);
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result[^1] = (byte)(crc >> 8);
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return result;
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}
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}
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