policy.h

 
//          Copyright John McFarlane 2019.
// 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_ELASTIC_TAG_POLICY_H)
#define CNL_IMPL_ELASTIC_TAG_POLICY_H
 
#include "../custom_operator/op.h"
 
#include <algorithm>
 
namespace cnl {
    namespace _impl {
        template<binary_arithmetic_op Operation, int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy;
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::add_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits = std::max(LhsDigits, RhsDigits) + 1;
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::subtract_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits =
                    std::max(LhsDigits, RhsDigits) + (LhsIsSigned | RhsIsSigned);
            static constexpr bool is_signed = true;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::multiply_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr auto contribution(int operand_digits)
            {
                return operand_digits == 1 ? 0 : operand_digits;
            }
            static constexpr int digits = std::max(1, contribution(LhsDigits) + contribution(RhsDigits));
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::divide_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits = LhsDigits;
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::modulo_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits = std::min(LhsDigits, RhsDigits);
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::bitwise_or_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits = std::max(LhsDigits, RhsDigits);
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::bitwise_and_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits = std::min(LhsDigits, RhsDigits);
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
 
        template<int LhsDigits, bool LhsIsSigned, int RhsDigits, bool RhsIsSigned>
        struct policy<_impl::bitwise_xor_op, LhsDigits, LhsIsSigned, RhsDigits, RhsIsSigned> {
            static constexpr int digits = std::max(LhsDigits, RhsDigits);
            static constexpr bool is_signed = LhsIsSigned || RhsIsSigned;
        };
    }
}
 
#endif  // CNL_IMPL_ELASTIC_TAG_POLICY_H