Implementing a join algorithm in Postgres

I have written a C program which reads from 3 files(Each file is table having 2 columns and thousands of rows).The program is used to join those 3 tables and the algorithm which I have written will work only for those 3 files. Now I want to test this program for postgres. Can someone tell me how to do that, where should I include this program so that I can successfully implement that program in postgres.

Thank you.

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