How does this work?

• llui mul_mod(llui a, llui b, llui m){
• llui y = (llui)((float64)a*(float64)b/m+(float64)1/2);
• y = y * m;
• llui x = a * b;
• llui r = x-y;
• if ( (lli)r < 0 ){
• r = r + m; y = y-1;
• }
• return r;
• }

For example if we do c = (a+b)%m;

What if a+b itself causes the overflow that is a+b is larger than the size of typeof a or b.

Doesn’t x in the above code cause overflow that is a*b is larger than a size of llui.

Here llui means long long unsigned int and lli means long long int and float64 stands for long double