Comparing fractions using pointers program in C efficient method

How to compare 2 fractions that are stored in pointer instances? consider the below code:

struct frac {
 int num;
 int denom;
};

We need to implement : fr_equal(a,b) returns true if *a is equal to *b.

bool fr_equal(const struct frac *a, const struct frac *b);

I am facing difficulties in this, my code is as below:

bool fr_equal(const struct frac *a, const struct frac *b) {

    if ( (*a).num != 0 && (*b).num !=0)
    {
        int x = (*a).num;
        int y = (*a).denom;
        int m = (*b).num;
        int n = (*b).denom;

        if (x==m && y==n )
            return true;

        if (x%y==0)
            y=y/x;
        else
            return false;
    }
    else
    {
        return false;
    }
}

My code is incomplete, as I haven't understood how to proceed and what all cases to consider. I could have 4 cases but its too long.

Can anyone tell me a short and efficient way of doing this

Thanks!