52 lines
1.5 KiB
C++
52 lines
1.5 KiB
C++
/*
|
|
* Copyright 2003-2021 The Music Player Daemon Project
|
|
* http://www.musicpd.org
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation; either version 2 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License along
|
|
* with this program; if not, write to the Free Software Foundation, Inc.,
|
|
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
|
|
*/
|
|
|
|
#ifndef MPD_BIT_REVERSE_HXX
|
|
#define MPD_BIT_REVERSE_HXX
|
|
|
|
#include <cstdint>
|
|
|
|
/**
|
|
* @see http://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64BitsDiv
|
|
*/
|
|
constexpr uint8_t
|
|
BitReverseMultiplyModulus(uint8_t _in) noexcept
|
|
{
|
|
uint64_t in = _in;
|
|
return uint8_t((in * 0x0202020202ULL & 0x010884422010ULL) % 1023);
|
|
}
|
|
|
|
/* in order to avoid including <array> in this header, this `struct`
|
|
is a workaround for GenerateBitReverseTable() being able to return
|
|
the plain array */
|
|
struct BitReverseTable {
|
|
uint8_t data[256];
|
|
};
|
|
|
|
extern const BitReverseTable bit_reverse_table;
|
|
|
|
[[gnu::const]]
|
|
static inline uint8_t
|
|
bit_reverse(uint8_t x) noexcept
|
|
{
|
|
return bit_reverse_table.data[x];
|
|
}
|
|
|
|
#endif
|