c++20/exercise-3-0.hpp

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// ===-- chapter-3/c++20/exercise-3-0.hpp ----------------- -*- C++ -*- --=== //
#ifndef EXERCISE_3_0
#define EXERCISE_3_0
 
#include <cstdint>
 
 
namespace exercise_3_0 {
 
inline namespace cpp20 {
 
consteval uint32_t checked_binary(uint64_t const N)
{
    // Even though "N" is a compile-time construct in consteval functions, it
    // cannot be used in things like static_assert or class template parameters.
    // An ad-hoc way of simulating the static_assert is to throw an exception,
    // which will give a compilation error with the provided string.
    if ((N % 10) > 1) { throw "N is not a binary number"; }
 
    return (N == 0) ? 0 : (N % 10) + (2 * checked_binary(N/10));
}
 
} // inline namespace cpp20
} // namespace exercise_3_0
 
#endif // EXERCISE_3_0