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/**
* Copyright (C) 2015 Kaspar Schleiser <kaspar@schleiser.de>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*
* Code taken from C FAQ (http://c-faq.com/lib/rand.html).
*/
/**
* @ingroup sys_random
* @{
* @file
*
* @brief Simple Park & Miller "minimal standard" PRNG
*
* This file contains a simple Park-Miller pseudo random number generator.
*
* While not very random when considering crypto requirements, this is probably
* random enough anywhere where pseudo-randomness is sufficient, e.g., when
* provided with a sensible seed source, for MAC algorithms.
*
* The implementation is taken from the C FAQ, but modified to use magic number
* division and adapted to RIOT's coding conventions..
*
* @author Kaspar Schleiser <kaspar@schleiser.de>
* @}
*/
#include <stdint.h>
#include "div.h"
#define a 48271
#define m 2147483647
#define q (m / a) /* 44488 */
#define r (m % a) /* 3399 */
static uint32_t _seed = 1;
int rand_minstd(void)
{
uint32_t hi = div_u32_by_44488(_seed);
uint32_t lo = div_u32_mod_44488(_seed);
uint32_t test = (a * lo) - (r * hi);
if(test > 0) {
_seed = test;
}
else {
_seed = test + m;
}
return _seed;
}
uint32_t random_uint32(void)
{
/* minstd as implemented returns only values from 1 to 2147483647,
* so run it two times to get 32bits */
uint16_t A = (rand_minstd() >> 15);
uint16_t B = (rand_minstd() >> 15);
return (((uint32_t)A) << 16) | B;
}
void random_init(uint32_t val)
{
if (!val) {
val = 1;
}
_seed = val;
}
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