36 lines
795 B
C++
36 lines
795 B
C++
// SPDX-License-Identifier: GPL-2.0-or-later
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// Copyright The Music Player Daemon Project
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#ifndef MPD_BIT_REVERSE_HXX
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#define MPD_BIT_REVERSE_HXX
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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 uint8_t
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BitReverseMultiplyModulus(uint8_t _in) noexcept
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{
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uint64_t in = _in;
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return uint8_t((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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uint8_t 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 uint8_t
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bit_reverse(uint8_t x) noexcept
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{
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return bit_reverse_table.data[x];
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}
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#endif
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