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