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/*
* Copyright (c) 2017 embedded brains GmbH. All rights reserved.
*
* embedded brains GmbH
* Dornierstr. 4
* 82178 Puchheim
* Germany
* <rtems@embedded-brains.de>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
/*
* 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 <unistd.h>
#include <string.h>
#include <rtems/sysinit.h>
#include <rtems/counter.h>
int getentropy(void *ptr, size_t n)
{
uint8_t *dest = ptr;
while (n > 0) {
rtems_counter_ticks ticks;
ticks = rtems_counter_read();
if (n >= sizeof(ticks)) {
memcpy(dest, &ticks, sizeof(ticks));
n -= sizeof(ticks);
dest += sizeof(ticks);
} else {
/*
* Fill the remaining bytes with only the least
* significant byte of the time. That is the byte with
* the most changes.
*/
*dest = ticks & 0xFF;
--n;
++dest;
}
}
return 0;
}
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