/****************************************************************************
 * include/nuttx/lib/xorshift128.h
 *
 *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
 *   Author: David S. Alessio
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/* This random number generator is simple, fast and portable.
 *      Ref:  https://en.wikipedia.org/wiki/Xorshift
 */

#ifndef __INCLUDE_NUTTX_LIB_XORSHIFT128_H
#define __INCLUDE_NUTTX_LIB_XORSHIFT128_H

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* Default XorShift128 state initializer */

#define XORSHIFT128_INITIALIZER { 97, 101, 97 << 17, 101 << 25 }

/****************************************************************************
 * Public Types
 ****************************************************************************/

/* Provides the state of the XorShift128 PRNG */

struct xorshift128_state_s
{
  uint32_t x;
  uint32_t y;
  uint32_t z;
  uint32_t w;
};

/****************************************************************************
 * Public Function Prototypes
 ****************************************************************************/

#ifdef __cplusplus
#define EXTERN extern "C"
extern "C"
{
#else
#define EXTERN extern
#endif

/****************************************************************************
 * Name: xorshift128
 *
 * Description:
 *   Generate one 32-bit pseudo-random number.
 *
 *   NOTE: Because the PRNG state is passed as a parameter, this function is
 *   fully re-entrant and may be called from an interrupt handler.
 *
 *   The downside to this is that users of the PRNG might not get as much
 *   entropy as if it were a common state structure.
 *
 * Input Parameters:
 *   state - The current XorShift128 state.
 *
 * Returned Value:
 *   The generated pseudo-random number
 *
 ****************************************************************************/

uint32_t xorshift128(FAR struct xorshift128_state_s *state);

#undef EXTERN
#ifdef __cplusplus
}
#endif

#endif /* __INCLUDE_NUTTX_LIB_XORSHIFT128_H */