Is there any reason that the destination IP address and port number are used in hashing before the source IP address and port number? As mentioned in the beginning of the data structure, you can find...

Is there any reason that the destination IP address and port number are used in hashing before the source IP address and port number?

As mentioned in the beginning of the data structure, you can find another implementation of token bucket in act_police.c . Explain how the token bucket is implemented for that policer.