Changes

The algorithm is as follows, provided that `data` is the list of the 20 first bytes, in the same order they arrived in.

   “”“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 )

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