text: /****************************************************************************
   * libc/misc/lib_xorshift.c
   *
   *   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
   */
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <sys/types.h>
  #include <stdint.h>
  #include <assert.h>
  
  #include <nuttx/lib/xorshift128.h>
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * 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)
  {
    uint32_t t;
  
    DEBUGASSERT(state != NULL);
  
    t        = state->x;
    t       ^= t << 11;
    t       ^= t >> 8;
  
    state->x = state->y;
    state->y = state->z;
    state->z = state->w;
  
    state->w ^= state->w >> 19;
    state->w ^= t;
  
    return state->w;
  }
  