C++ - How to left/right circular shift a bitset?

Question

Let's say I have a std::bitset<28> called left28. I'm looking to left circular shift left28.

After doing some searching, I came across std::rotl (C++20) but it doesn't seem to play nice with bitset, so I have no idea how I'm going to pull this off.

Answer 1

You can implement a left circular shift by combining right shifts with left shifts.

template<size_t N>
std::bitset<N> rotl( std::bitset<N> const& bits, unsigned count )
{
             count %= N;  // Limit count to range [0,N)
             return bits << count | bits >> (N - count);
// The shifted bits ^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^ The wrapped bits
}

Note that unlike std::rotl, the count in this example is unsigned.

If you would like it to be signed, like an int, write a matching rotr and have each function call the other when count is negative.