mirror of https://github.com/TomHarte/CLK.git
60 lines
1.4 KiB
C++
60 lines
1.4 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 <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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struct ReverseTable {
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static constexpr std::array<uint8_t, 256> reverse_table() {
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std::array<uint8_t, 256> map{};
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for(std::size_t c = 0; c < 256; ++c) {
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map[c] = uint8_t(
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((c & 0x80) >> 7) |
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((c & 0x40) >> 5) |
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((c & 0x20) >> 3) |
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((c & 0x10) >> 1) |
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((c & 0x08) << 1) |
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((c & 0x04) << 3) |
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((c & 0x02) << 5) |
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((c & 0x01) << 7)
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);
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}
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return map;
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}
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};
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const std::array<uint8_t, 256> map = ReverseTable::reverse_table();
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return map[source];
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}
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// All other versions just call the byte-level reverse the appropriate number of times.
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template <typename IntT> constexpr IntT bit_reverse(IntT source) {
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IntT result;
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uint8_t *src = reinterpret_cast<uint8_t *>(&source);
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uint8_t *dest = reinterpret_cast<uint8_t *>(&result) + sizeof(result) - 1;
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for(size_t c = 0; c < sizeof(source); c++) {
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*dest = bit_reverse(*src);
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++src;
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--dest;
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}
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return result;
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}
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}
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