core-bitops.h

/*
 * Copyright (C) 2022-2023 Colin Ian King.
 *
 * 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 CORE_BITOPS_H
#define CORE_BITOPS_H

/*
 *  stress_reverse64
 *	generic fast-ish 64 bit reverse
 */
static inline uint64_t stress_reverse64(register uint64_t x)
{
#if defined(HAVE_BUILTIN_BITREVERSE)
	return __builtin_bitreverse64(x);
#else
	x = (((x & 0xaaaaaaaaaaaaaaaaULL) >> 1)  | ((x & 0x5555555555555555ULL) << 1));
	x = (((x & 0xccccccccccccccccULL) >> 2)  | ((x & 0x3333333333333333ULL) << 2));
	x = (((x & 0xf0f0f0f0f0f0f0f0ULL) >> 4)  | ((x & 0x0f0f0f0f0f0f0f0fULL) << 4));
	x = (((x & 0xff00ff00ff00ff00ULL) >> 8)  | ((x & 0x00ff00ff00ff00ffULL) << 8));
	x = (((x & 0xffff0000ffff0000ULL) >> 16) | ((x & 0x0000ffff0000ffffULL) << 16));
	return ((x >> 32) | (x << 32));
#endif
}

/*
 *  stress_reverse32
 *	generic fast-ish 32 bit reverse
 */
static inline uint32_t stress_reverse32(register uint32_t x)
{
#if defined(HAVE_BUILTIN_BITREVERSE)
	return __builtin_bitreverse32(x);
#else
	x = (((x & 0xaaaaaaaaUL) >> 1)  | ((x & 0x55555555UL) << 1));
	x = (((x & 0xccccccccUL) >> 2)  | ((x & 0x33333333UL) << 2));
	x = (((x & 0xf0f0f0f0UL) >> 4)  | ((x & 0x0f0f0f0fUL) << 4));
	x = (((x & 0xff00ff00UL) >> 8)  | ((x & 0x00ff00ffUL) << 8));
	x = (((x & 0xffff0000UL) >> 16) | ((x & 0x0000ffffUL) << 16));
	return x;
#endif
}

/*
 *  stress_reverse16
 *	generic fast-ish 16 bit reverse
 */
static inline uint16_t stress_reverse16(register uint16_t x)
{
#if defined(HAVE_BUILTIN_BITREVERSE)
	return __builtin_bitreverse16(x);
#else
	x = (((x & 0xaaaaUL) >> 1)  | ((x & 0x5555UL) << 1));
	x = (((x & 0xccccUL) >> 2)  | ((x & 0x3333UL) << 2));
	x = (((x & 0xf0f0UL) >> 4)  | ((x & 0x0f0fUL) << 4));
	x = (((x & 0xff00UL) >> 8)  | ((x & 0x00ffUL) << 8));
	return x;
#endif
}

/*
 *  stress_reverse8
 *	generic fast-ish 8 bit reverse
 */
static inline uint8_t stress_reverse8(register uint8_t x)
{
#if defined(HAVE_BUILTIN_BITREVERSE)
	return __builtin_bitreverse8(x);
#else
	x = (((x & 0xaaUL) >> 1)  | ((x & 0x55UL) << 1));
	x = (((x & 0xccUL) >> 2)  | ((x & 0x33UL) << 2));
	x = (((x & 0xf0UL) >> 4)  | ((x & 0x0fUL) << 4));
	return x;
#endif
}

#endif