95 lines
3.3 KiB
C
95 lines
3.3 KiB
C
/****************************************************************************
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* libc/misc/lib_xorshift.c
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Author: David S. Alessio
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/* This random number generator is simple, fast and portable.
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* Ref: https://en.wikipedia.org/wiki/Xorshift
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*/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <stdint.h>
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#include <assert.h>
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#include <nuttx/lib/xorshift128.h>
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: xorshift128
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*
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* Description:
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* Generate one 32-bit pseudo-random number.
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*
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* NOTE: Because the PRNG state is passed as a parameter, this function is
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* fully re-entrant and may be called from an interrupt handler.
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*
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* The downside to this is that users of the PRNG might not get as much
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* entropy as if it were a common state structure.
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*
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* Input Parameters:
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* state - The current XorShift128 state.
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*
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* Returned Value:
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* The generated pseudo-random number
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*
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****************************************************************************/
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uint32_t xorshift128(FAR struct xorshift128_state_s *state)
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{
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uint32_t t;
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DEBUGASSERT(state != NULL);
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t = state->x;
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t ^= t << 11;
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t ^= t >> 8;
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state->x = state->y;
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state->y = state->z;
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state->z = state->w;
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state->w ^= state->w >> 19;
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state->w ^= t;
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return state->w;
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}
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