In order to write a code that enable you to do multiplication and exponentiation in finite field between numbers greater than 2^(64), you have to copy and paste the few lines of important_file.c in your main and outside the main you have to write #include "big_galois_lib.c" (just to inlude the big_galois_lib.c file in your code and to call the functions you want). Then you can compute, for example, multiplication in finite field GF(2^l) between "b" and "c" (both written as arrays of bools), just writing in your main:
bool * a;
a = malloc(l * sizeof(bool));
a = big_galois_mul(b,c, l, poly_irr[l]);
Finally, "a" will be a bool array corresponding to the binary representation of the result of the multiplication.
File example.c is just a short example.