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# Author: Paul Goins
# License (this module only): PUBLIC DOMAIN
import sys
def get_bits(message):
"""Yields bits of message in MSB to LSB order"""
for char in message:
byte = ord(char)
for i in xrange(7, -1, -1):
yield ((byte >> i) & 0x1)
def bit_by_bit(message, poly=0x04c11db7, width=32, init=0):
reg = init
#print "MESSAGE:", repr(message)
#print "BITS:", list(get_bits(message))
message += chr(0)*(width/8) # Pad message for CRC width
#print "MESSAGE:", repr(message)
#print "BITS:", list(get_bits(message))
for bit in get_bits(message):
# Shift new bit in
reg = (reg << 1) | bit
# Handle and track register overflow
do_xor = ((reg & 0x100000000) != 0)
reg &= 0xFFFFFFFF
# In case of overflow, perform xor
if do_xor:
reg ^= poly
#print "REG: {0:08X}".format(reg)
return reg
def direct_table_with_padding(message):
return 0
def direct_table(message):
return 0
def main():
message = "123456789"
for method in bit_by_bit, direct_table_with_padding, direct_table:
crc = method(message)
print "{0:50s}: {1:08X}".format(str(method), crc)
if __name__ == "__main__":
sys.exit(main())
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