36 lines
928 B
Python
36 lines
928 B
Python
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import itertools
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from .ntype import BigStream, uint32
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def calculate_crc(self):
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t1 = t2 = t3 = t4 = t5 = t6 = 0xDF26F436
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u32 = 0xFFFFFFFF
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m1 = self.read_bytes(0x1000, 0x100000)
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words = map(uint32.value, zip(m1[0::4], m1[1::4], m1[2::4], m1[3::4]))
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m2 = self.read_bytes(0x750, 0x100)
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words2 = map(uint32.value, zip(m2[0::4], m2[1::4], m2[2::4], m2[3::4]))
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for d, d2 in zip(words, itertools.cycle(words2)):
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# keep t2 and t6 in u32 for comparisons; others can wait to be truncated
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if ((t6 + d) & u32) < t6:
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t4 += 1
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t6 = (t6+d) & u32
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t3 ^= d
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shift = d & 0x1F
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r = ((d << shift) | (d >> (32 - shift)))
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t5 += r
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if t2 > d:
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t2 ^= r & u32
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else:
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t2 ^= t6 ^ d
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t1 += d2 ^ d
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crc0 = (t6 ^ t4 ^ t3) & u32
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crc1 = (t5 ^ t2 ^ t1) & u32
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return uint32.bytes(crc0) + uint32.bytes(crc1)
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