34 lines
836 B
C++
34 lines
836 B
C++
// SPDX-License-Identifier: GPL-2.0-or-later
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// Copyright The Music Player Daemon Project
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#pragma once
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#include <cstddef>
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#include <cstdint>
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/**
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* @see http://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64BitsDiv
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*/
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constexpr std::byte
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BitReverseMultiplyModulus(std::byte _in) noexcept
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{
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uint64_t in = static_cast<uint64_t>(_in);
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return static_cast<std::byte>((in * 0x0202020202ULL & 0x010884422010ULL) % 1023);
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}
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/* in order to avoid including <array> in this header, this `struct`
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is a workaround for GenerateBitReverseTable() being able to return
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the plain array */
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struct BitReverseTable {
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std::byte data[256];
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};
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extern const BitReverseTable bit_reverse_table;
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[[gnu::const]]
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static inline std::byte
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BitReverse(std::byte x) noexcept
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{
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return bit_reverse_table.data[static_cast<std::size_t>(x)];
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}
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