/in/foo.cc: In function 'int main()':
/in/foo.cc:33:12: warning: iteration 8 invokes undefined behavior [-Waggressive-loop-optimizations]
    f[x+mx[i]][y+my[i]]=1;
        ~~~~^
/in/foo.cc:3:33: note: within this loop
 #define rep(i,a,b) for(int i=a;i<=b;i++)
                                  
/in/foo.cc:32:8:
    rep(i,1,9)
        ~~~~~                     
/in/foo.cc:32:4: note: in expansion of macro 'rep'
    rep(i,1,9)
    ^~~