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27 lines
648 B
Python
27 lines
648 B
Python
"""
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coax.parity
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~~~~~~~~~~~
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Single byte parity computation
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"""
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# From http://p-nand-q.com/python/algorithms/math/bit-parity.html
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def _parallel_swar(i):
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i = i - ((i >> 1) & 0x55555555)
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i = (i & 0x33333333) + ((i >> 2) & 0x33333333)
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i = (((i + (i >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24
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return int(i % 2)
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_PARITY_LOOKUP = [_parallel_swar(i) for i in range(256)]
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def even_parity(byte):
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"""Compute even parity"""
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if byte < 0 or byte > 255:
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raise ValueError('Input must be between 0 and 255')
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return _PARITY_LOOKUP[byte]
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def odd_parity(byte):
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"""Compute odd parity"""
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return int(not even_parity(byte))
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