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27 lines
689 B
Python
27 lines
689 B
Python
"""Helper functions."""
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from ctypes import c_ushort
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def calculate_crc16(input_data: bytes) -> int:
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"""Calculate the CRC-16 of a byte string."""
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crc16_tab = []
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crc16_constant = 0xA001
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for i in range(0, 256):
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crc = c_ushort(i).value
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for j in range(0, 8):
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if crc & 0x0001:
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crc = c_ushort(crc >> 1).value ^ crc16_constant
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else:
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crc = c_ushort(crc >> 1).value
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crc16_tab.append(hex(crc))
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crcValue = 0xFFFF
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for c in input_data:
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tmp = crcValue ^ c
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rotated = c_ushort(crcValue >> 8).value
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crcValue = rotated ^ int(crc16_tab[(tmp & 0x00FF)], 0)
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return crcValue
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