c++ - Multiplying __int64's -

can explain me (in detail) how multiply 2 __int64 objs , check if result fit in __int64.

note: not use compiler or processor dependent routines.

not assuming a , b positive:

__int64 a,b; //... __int64  tmp_result = abs(a) * abs(b) ; if (     ( && b ) &&     (      ( tmp_result < abs(a) || tmp_result < abs(b) ) ||      ( tmp_result / abs(a) != abs(b)) ||      ( == type_min && b != 1) ||      ( b == type_min && != 1)     )    )    std::cout << "overflow"; __int64 result = * b; 

edit: adding corner cases code.

edit: in opinion ( && * b / != b) enough.