Question

I’d like to do an unsigned shift in C++. Here’s my example code. The problem with it is it isn’t generic. This code is completely wrong. It will not work on longs and it wont work on smaller types like char. I tried (unsigned T) but that is a syntax error. How might i make this generic without specialization?

#include <cassert>
template<class T>
T unsigned_shift(const T&t, int s) { return ((unsigned int)t)>>s; }
int main()
{
    assert(unsigned_shift(-1, 2)==(-1u>>2));
    assert(unsigned_shift((char)-1, 2)==64);
}

Answer 1

If you can use Boost, the type_traits library has the make_unsigned template that would fit your needs perfectly.

#include <boost/type_traits/make_unsigned.hpp>

template<class T>
T unsigned_shift(const T&t, unsigned int s)
{
    return ((make_unsigned<T>::type)t)>>s;
}

(I changed the type of s to unsigned int because the operation of the shift operators is undefined for negative values of the second operand – see §5.8 ¶1)