used_digits.h

 
//          Copyright John McFarlane 2018.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file ../LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)
 
#if !defined(CNL_IMPL_USED_DIGITS_H)
#define CNL_IMPL_USED_DIGITS_H
 
#include "../integer.h"
 
#include <limits>
#include <type_traits>
 
namespace cnl {
    namespace _impl {
 
        // cnl::_impl::used_digits
 
        template<bool IsSigned>
        struct used_digits_signed;
 
        template<>
        struct used_digits_signed<false> {
            template<integer Integer>
            [[nodiscard]] constexpr auto operator()(Integer const& value, int radix) const -> int
            {
                return (value > 0) ? 1 + used_digits_signed<false>{}(value / radix, radix) : 0;
            }
        };
 
        template<>
        struct used_digits_signed<true> {
            template<integer Integer>
            [[nodiscard]] constexpr auto operator()(Integer const& value, int radix) const
            {
                // Most negative number is not exploited;
                // thus negating the result or subtracting it from something else
                // will less likely result in overflow.
                return (value < 0) ? used_digits_signed<false>{}(Integer(-1) - value, radix)
                                   : used_digits_signed<false>{}(value, radix);
            }
        };
 
        template<integer Integer>
        [[nodiscard]] constexpr auto used_digits(
                Integer const& value, int radix = std::numeric_limits<Integer>::radix)
        {
            return used_digits_signed<std::is_signed<Integer>::value>{}(value, radix);
        }
    }
}
 
#endif  // CNL_IMPL_USED_DIGITS_H