CLK/Numeric/NumericCoder.hpp

//
//  NumericCoder.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 17/01/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#ifndef NumericCoder_hpp
#define NumericCoder_hpp

namespace Numeric {

/// Stores and retrieves an arbitrary number of fields into an int with arbitrary modulos.
///
/// E.g. NumericEncoder<8, 3, 14> establishes an encoder and decoder for three fields,
/// the first is modulo 8, the second is modulo 3, the third is modulo 14.
///
/// NumericEncoder<8, 3, 14>::encode<2>(v, 9) will mutate v so that the third field
/// (i.e. field 2) has value 9.
template <int... Sizes> class NumericCoder {
	public:
		/// Modifies @c target to hold @c value at @c index.
		template <int index> static void encode(int &target, int value) {
			static_assert(index < sizeof...(Sizes), "Index must be within range");
			NumericEncoder<Sizes...>::template encode<index, 0, 1>(target, value);
		}
		/// @returns The value from @c source at @c index.
		template <int index> static int decode(int source) {
			static_assert(index < sizeof...(Sizes), "Index must be within range");
			return NumericDecoder<Sizes...>::template decode<index, 0, 1>(source);
		}

	private:

		template <int size, int... Tail>
		struct NumericEncoder {
			template <int index, int i, int divider> static void encode(int &target, int value) {
				if constexpr (i == index) {
					const int suffix = target % divider;
					target /= divider;
					target -= target % size;
					target += value % size;
					target *= divider;
					target += suffix;
				} else {
					NumericEncoder<Tail...>::template encode<index, i+1, divider*size>(target, value);
				}
			}
		};

		template <int size, int... Tail>
		struct NumericDecoder {
			template <int index, int i, int divider> static int decode(int source) {
				if constexpr (i == index) {
					return (source / divider) % size;
				} else {
					return NumericDecoder<Tail...>::template decode<index, i+1, divider*size>(source);
				}
			}
		};
};

}

#endif /* NumericCoder_hpp */