calculate number of bits set in byte

Question

I am interested, which is the optimal way of calculating the number of bits set in byte by this way

template< unsigned char byte > class BITS_SET
{
pub         


        

Answer 1

Using C++17 you can precalculate the lookup table using a constexpr lambda. Easier to reason about the correctness of it rather than a ready copy-pasted table.

#include 

static constexpr auto bitsPerByteTable = [] {
  std::array table{};
  for (decltype(table)::size_type i = 0; i < table.size(); i++) {
    table.at(i) = table.at(i / 2) + (i & 1);
  }
  return table;
}();