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@shirriff shirriff/ac3.py
Created Dec 7, 2017

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Create checksums for an air conditioner remote control
import re
# Each line is 3 bytes of input and the observed 1-byte checksum
data="""\
10100001 10010011 01100011 => 01110111
10100001 10010011 01100100 => 01110001
10100001 10010011 01100101 => 01110000
10100001 10010011 01100110 => 01110010
10100001 10010011 01100111 => 01110011
10100001 10010011 01101000 => 01111001
10100001 10010011 01101001 => 01111000
10100001 10010011 01101010 => 01111010
10100001 10010011 01101011 => 01111011
10100001 10010011 01101100 => 01111110
10100001 10010011 01101101 => 01111111
10100001 10010011 01101110 => 01111100
10100001 10010011 01101111 => 01111101
10100001 10010011 01110001 => 01100100
10100001 10010011 01110010 => 01100110
10100001 10010011 01110011 => 01100111
10100001 10010011 01110100 => 01100001
10100001 10010011 01110101 => 01100000
10100001 10010011 01110111 => 01100011
10100001 10010011 01110111 => 01100011
10100001 10010011 01111000 => 01101001
10100001 10010011 01101000 => 01111001
10100001 00010011 01101000 => 11111001
10100001 00010011 01101100 => 11111110
10100001 10010011 01101100 => 01111110
10100001 10010100 01111110 => 01101011
10100001 10000010 01101100 => 01100000
10100001 10000001 01101100 => 01100011
10100001 10010011 01101100 => 01111110
10100001 10010000 01101100 => 01111100
10100001 10011000 01101100 => 01110100
10100001 10001000 01101100 => 01101100
10100001 10010000 01101100 => 01111100
10100001 10011000 01101100 => 01110100
10100010 00000010 11111111 => 01111110"""
# Reverse bits in 8-bit value
def bitreverse(x):
return int('{:08b}'.format(x)[::-1], 2)
for line in data.split('\n'):
# Create inbytes (byte values) and checksum (bit string) from input line
inbits, checksum = line.split(' => ')
inbytes = [int(x, 2) for x in inbits.split(' ')]
# Compute the result checksum byte
inbytes = map(bitreverse, inbytes)
xorpart = (inbytes[0] ^ inbytes[1] ^ inbytes[2] ^ 0x4) & 0xf
sumpart = (inbytes[0] >> 4) + (inbytes[1] >> 4) + (inbytes[2] >> 4) + (inbytes[2] & 1) + ((inbytes[1] >> 3) & 1) + 1
sumpart = (-sumpart) & 0xf
result = bitreverse((sumpart << 4) | xorpart)
# Check the result and print
if checksum != '{:08b}'.format(result): print '** ERROR **',
print line, '{:08b}'.format(result)
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