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/* SPDX-License-Identifier: BSD-2-Clause */
/*
* Copyright (c) 2017 embedded brains GmbH. All rights reserved.
*
* 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.
*
* 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.
*/
/*
* ATTENTION: THIS IS A VERY LIMITED ENTROPY SOURCE.
*
* This implementation uses a time-based value for it's entropy. The only thing
* that makes it random are interrupts from external sources. Don't use it if
* you need for example a strong crypto.
*/
#include <sys/param.h>
#include <unistd.h>
#include <string.h>
#include <rtems/bsd.h>
#include <rtems/counter.h>
#include <rtems/sysinit.h>
static uint32_t state;
int getentropy(void *ptr, size_t n)
{
uint8_t *dest = ptr;
state ^= rtems_counter_read();
state *= 25169206;
state += 1679610226;
while (n > 0) {
size_t m;
m = MIN(n, sizeof(state));
memcpy(dest, &state, m);
n -= m;
dest += m;
state *= 85236167;
state += 30557471;
}
return 0;
}
static void getentropy_init(void)
{
struct bintime bt;
rtems_bsd_bintime(&bt);
state = (uint32_t) bt.frac;
state ^= (uint32_t) (bt.frac >> 32);
state ^= (uint32_t) bt.sec;
state ^= (uint32_t) (bt.sec >> 32);
}
RTEMS_SYSINIT_ITEM(
getentropy_init,
RTEMS_SYSINIT_DEVICE_DRIVERS,
RTEMS_SYSINIT_ORDER_LAST_BUT_5
);
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