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45 lines
1.3 KiB
C++
45 lines
1.3 KiB
C++
//
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// BitReverse.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 05/01/2023.
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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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#include "Sizes.hpp"
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#include <array>
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#include <cstdint>
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namespace Numeric {
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/// @returns @c source with the order of its bits reversed. E.g. if @c IntT is @c uint8_t then
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/// the reverse of bit pattern abcd efgh is hgfd dcba.
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template <typename IntT> constexpr IntT bit_reverse(IntT source);
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// The single-byte specialisation uses a lookup table.
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template<> constexpr uint8_t bit_reverse<uint8_t>(uint8_t source) {
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source = uint8_t(((source & 0b1111'0000) >> 4) | ((source & 0b0000'1111) << 4));
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source = uint8_t(((source & 0b1100'1100) >> 2) | ((source & 0b0011'0011) << 2));
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source = uint8_t(((source & 0b1010'1010) >> 1) | ((source & 0b0101'0101) << 1));
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return source;
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}
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// All other versions recursively subdivide.
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template <typename IntT>
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constexpr IntT bit_reverse(const IntT source) {
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static_assert(std::is_same_v<IntT, uint16_t> || std::is_same_v<IntT, uint32_t> || std::is_same_v<IntT, uint64_t>);
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constexpr auto HalfSize = sizeof(IntT) * 4;
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using HalfIntT = uint_t<HalfSize>;
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return IntT(
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IntT(bit_reverse(HalfIntT(source >> HalfSize))) |
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IntT(bit_reverse(HalfIntT(source))) << HalfSize
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);
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}
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}
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