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
↵
- 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
- if ( (lli)r < 0 ){↵
- r = r + m; y = y
- }↵
- 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
