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