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/*
* Copyright (C) 2024-2025 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_MWC_H
#define CORE_MWC_H
#include <stdint.h>
#include "core-attribute.h"
/*
* Use modulo reduction, this uses multiplication and shift
* which is normally faster than mask and compare looping.
* 32 bit systems generally don't have 128 unsigned integer
* multiplication support required for 64 bit modulo reduction
* so fast modulo reduction only works for 8, 16, 32 bits for
* these smaller systems.
*/
#define HAVE_FAST_MODULO_REDUCTION
extern void stress_mwc_reseed(void);
extern void stress_mwc_set_seed(const uint32_t w, const uint32_t z);
extern void stress_mwc_get_seed(uint32_t *w, uint32_t *z);
extern void stress_mwc_seed(void);
extern uint8_t stress_mwc1(void);
extern uint8_t stress_mwc8(void);
extern uint16_t stress_mwc16(void);
extern uint32_t stress_mwc32(void);
extern uint64_t stress_mwc64(void);
extern void stress_rndbuf(void *buf, const size_t len);
extern void stress_rndstr(char *str, const size_t len);
#if defined(HAVE_FAST_MODULO_REDUCTION)
/*
* stress_mwc8modn()
* see https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
* return 8 bit non-modulo biased value 1..max (inclusive)
* where max is most probably not a power of 2
*/
static inline uint8_t stress_mwc8modn(const uint8_t max)
{
return (uint8_t)(((uint16_t)stress_mwc8() * (uint16_t)max) >> 8);
}
/*
* stress_mwc16modn()
* see https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
* return 16 bit non-modulo biased value 1..max (inclusive)
*/
static inline uint16_t stress_mwc16modn(const uint16_t max)
{
return (uint16_t)(((uint32_t)stress_mwc16() * (uint32_t)max) >> 16);
}
/*
* stress_mwc32modn()
* see https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
* return 32 bit non-modulo biased value 1..max (inclusive)
*/
static inline uint32_t stress_mwc32modn(const uint32_t max)
{
return (uint32_t)(((uint64_t)stress_mwc32() * (uint64_t)max) >> 32);
}
#else
extern uint8_t stress_mwc8modn(const uint8_t max);
extern uint16_t stress_mwc16modn(const uint16_t max);
extern uint32_t stress_mwc32modn(const uint32_t max);
#endif
#if defined(HAVE_FAST_MODULO_REDUCTION) && \
defined(HAVE_INT128_T)
/*
* stress_mwc64modn()
* see https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction
* return 64 bit non-modulo biased value 1..max (inclusive)
*/
static inline uint64_t stress_mwc64modn(const uint64_t max)
{
return (uint64_t)(((__uint128_t)stress_mwc64() * (__uint128_t)max) >> 64);
}
#else
extern uint64_t stress_mwc64modn(const uint64_t max);
#endif
#endif
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