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75 lines
2.2 KiB
C++
75 lines
2.2 KiB
C++
//
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// NumericCoder.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 17/01/2023.
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// Copyright © 2023 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace Numeric {
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/// Stores and retrieves an arbitrary number of fields into an int with arbitrary modulos.
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///
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/// E.g. NumericCoder<8, 3, 14> establishes an encoder and decoder for three fields,
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/// the first is modulo 8, the second is modulo 3, the third is modulo 14.
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///
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/// NumericCoder<8, 3, 14>::encode<2>(v, 9) will mutate v so that the third field
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/// (i.e. field 2) has value 9.
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///
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/// The first given field will occupy the least significant part of the target int; e.g.
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/// a NumericCoder<3, 4, 6> with ::encode<0>(v, 2), ::encode<1>(v, 1) and
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/// ::encode<2>(v, 5) will have a final value of:
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///
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/// [value] 2 +
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/// [value] 1 * [product of previous field sizes] 3 +
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/// 5 * 12
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/// = 65
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///
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template <int... Sizes> class NumericCoder {
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public:
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/// Modifies @c target to hold @c value at @c index.
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template <int index> static void encode(int &target, int value) {
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static_assert(index < sizeof...(Sizes), "Index must be within range");
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NumericEncoder<Sizes...>::template encode<index>(target, value);
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}
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/// @returns The value from @c source at @c index.
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template <int index> static int decode(int source) {
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static_assert(index < sizeof...(Sizes), "Index must be within range");
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return NumericDecoder<Sizes...>::template decode<index>(source);
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}
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private:
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template <int size, int... Tail>
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struct NumericEncoder {
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template <int index, int i = 0, int divider = 1> static void encode(int &target, int value) {
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if constexpr (i == index) {
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const int suffix = target % divider;
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target /= divider;
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target -= target % size;
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target += value % size;
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target *= divider;
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target += suffix;
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} else {
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NumericEncoder<Tail...>::template encode<index, i+1, divider*size>(target, value);
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}
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}
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};
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template <int size, int... Tail>
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struct NumericDecoder {
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template <int index, int i = 0, int divider = 1> static int decode(int source) {
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if constexpr (i == index) {
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return (source / divider) % size;
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} else {
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return NumericDecoder<Tail...>::template decode<index, i+1, divider*size>(source);
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}
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}
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};
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};
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}
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