Need simple firewall function

[wang20150419]

Such as:
      The configuration file is rewritten as:

table {
       # If no port is specified the port of the incoming listener is used
       example.com 192.0.2.10 | 166.111.8.0/24,58.48.0.0/13
       example.net 192.0.2.20
}

Indicates that only addresses from 166.111.8.0/24 and 58.48.0.0/13 can access example.com.

I am a C programmer. Where can I modify this source code to achieve this function? Can you give me some tips?