79 lines
2.2 KiB
Python
79 lines
2.2 KiB
Python
custom_crc_table = {}
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def generate_crc32_table(_poly):
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global custom_crc_table
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for i in range(256):
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c = i << 24
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for j in range(8):
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c = (c << 1) ^ _poly if (c & 0x80000000) else c << 1
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custom_crc_table[i] = c & 0xffffffff
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def crc32_stm(bytes_arr):
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length = len(bytes_arr)
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crc = 0xffffffff
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k = 0
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while length >= 4:
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v = ((bytes_arr[k] << 24) & 0xFF000000) | ((bytes_arr[k+1] << 16) & 0xFF0000) | \
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((bytes_arr[k+2] << 8) & 0xFF00) | (bytes_arr[k+3] & 0xFF)
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crc = ((crc << 8) & 0xffffffff) ^ custom_crc_table[0xFF & ((crc >> 24) ^ v)]
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crc = ((crc << 8) & 0xffffffff) ^ custom_crc_table[0xFF & ((crc >> 24) ^ (v >> 8))]
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crc = ((crc << 8) & 0xffffffff) ^ custom_crc_table[0xFF & ((crc >> 24) ^ (v >> 16))]
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crc = ((crc << 8) & 0xffffffff) ^ custom_crc_table[0xFF & ((crc >> 24) ^ (v >> 24))]
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k += 4
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length -= 4
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if length > 0:
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v = 0
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for i in range(length):
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v |= (bytes_arr[k+i] << 24-i*8)
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if length == 1:
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v &= 0xFF000000
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elif length == 2:
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v &= 0xFFFF0000
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elif length == 3:
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v &= 0xFFFFFF00
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crc = (( crc << 8 ) & 0xffffffff) ^ custom_crc_table[0xFF & ( (crc >> 24) ^ (v ) )];
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crc = (( crc << 8 ) & 0xffffffff) ^ custom_crc_table[0xFF & ( (crc >> 24) ^ (v >> 8) )];
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crc = (( crc << 8 ) & 0xffffffff) ^ custom_crc_table[0xFF & ( (crc >> 24) ^ (v >> 16) )];
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crc = (( crc << 8 ) & 0xffffffff) ^ custom_crc_table[0xFF & ( (crc >> 24) ^ (v >> 24) )];
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return crc
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poly = 0x04C11DB7
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buf = bytes(reversed([1, 2, 3, 4]))
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generate_crc32_table(poly)
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print(hex(crc32_stm(bytearray(buf))))
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from crccheck import crc
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import struct
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def rev_bits_in_word(w):
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return sum( ((w>>i)&1) << (31-i) for i in range(32) )
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import zlib
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def crc32stm(inbytes):
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crc32 = crc.Crc32.calc(inbytes)^0xffffffff
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#crc32 = zlib.crc32(inbytes)^0xffffffff
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crc32 = rev_bits_in_word(crc32)
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return crc32
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#data = [0x80,0x40,0xc0,0x20]
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data = [0x00, 0, 0, 0x80, 0, 0, 0, 0x80]
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print(hex(crc32stm(bytes(data))))
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print(hex(zlib.crc32(bytes([0, 0, 0, 1]))^0xffffffff))
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