mirror of https://github.com/m-labs/artiq.git
36 lines
1.1 KiB
Python
36 lines
1.1 KiB
Python
class CRC:
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"""Generic and simple table driven CRC calculator.
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This implementation is:
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* MSB first data
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* "un-reversed" full polynomial (i.e. starts with 0x1)
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* no initial complement
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* no final complement
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Handle any variation on those details outside this class.
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>>> r = CRC(0x1814141AB)(b"123456789") # crc-32q
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>>> assert r == 0x3010BF7F, hex(r)
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"""
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def __init__(self, poly, data_width=8):
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self.poly = poly
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self.crc_width = poly.bit_length() - 1
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self.data_width = data_width
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self._table = [self._one(i << self.crc_width - data_width)
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for i in range(1 << data_width)]
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def _one(self, i):
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for j in range(self.data_width):
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i <<= 1
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if i & 1 << self.crc_width:
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i ^= self.poly
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return i
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def __call__(self, msg, crc=0):
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for data in msg:
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p = data ^ crc >> self.crc_width - self.data_width
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q = crc << self.data_width & (1 << self.crc_width) - 1
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crc = self._table[p] ^ q
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return crc
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