Tc Filter - Port Ranges Calculate Mask Value

i,

I need to support port ranges in tc filter rules.

I know how to formulate the rule but , I am not able to understand how
to calculate the mask value to segregate the port values that lie
within a perticular range .

I got the following sample

"tc filter add dev eth1 parent 1:1 protocol ip prio 10 u32 match ip
sport 0x1ae0 0x1ff0 flowid 1:10 This rule will match all ports from
6880 to 6895. "

This rule correctly matches port range from 6880 to 6895. But I am
unable to figure out , how the mask value 0x1ff0 has been calculated.

I am picking up port ranges from GUI. So the range can be any and I
need to calculte mask value so as to find out which ports lie within
the entered range.

Suppose user has entered the port range as 10 -20. Then what should be
the mask value corresponding to this range.

Please if you have any link, clue or reference material , do share it.

Thanking You
Anshul Makkar

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