gistfile1.c

// The function is supposed to return false when 
// x+y overflows unsigned short.
// Does the function do it correctly?
bool  IsValidAddition( unsigned short x, 
                       unsigned short y) {
    if (x+y < x)
         return false;
    return true;
}

During arithmetic operations, the C99 standard states that "if an int can represent all values of the original type, the value is converted to an int; otherwise, it is converted to an unsigned int."

Therefore this will never work to check for overflow.