The algorithm is as follows, provided that `data` is the list of the 20 first bytes, in the same order they arrived in.
<br /> def checksum(data):
“”“Compute and return the checksum as an int.”“”
# group the data by word, little-endian
data_list = []
for t in range(10):
data_list.append( data2*t + (data2*t+1<<8) )
# compute the checksum on 32 bits
chk32 = 0
for d in data_list:
chk32 = (chk32 << 1) + d
# return a value wrapped around on 15bits, and truncated to still fit into 15 bits
checksum = (chk32 & 0x7FFF) + ( chk32 >> 15 ) # wrap around to fit into 15 bits
checksum = checksum & 0x7FFF # truncate to 15 bits
return int( checksum )
<br />