123 lines
3.2 KiB
C
123 lines
3.2 KiB
C
/*
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* Copyright (c) 2017 Intel Corporation
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*
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* SPDX-License-Identifier: CC0-1.0
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*
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* Based on code written in 2016 by David Blackman and Sebastiano Vigna
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* (vigna@acm.org)
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*
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* To the extent possible under law, the author has dedicated all copyright
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* and related and neighboring rights to this software to the public domain
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* worldwide. This software is distributed without any warranty.
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*
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* See <http://creativecommons.org/publicdomain/zero/1.0/>.
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*/
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/* This is the successor to xorshift128+. It is the fastest full-period
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* generator passing BigCrush without systematic failures, but due to the
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* relatively short period it is acceptable only for applications with a
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* mild amount of parallelism; otherwise, use a xorshift1024* generator.
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*
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* Beside passing BigCrush, this generator passes the PractRand test suite
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* up to (and included) 16TB, with the exception of binary rank tests, as
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* the lowest bit of this generator is an LSFR. The next bit is not an
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* LFSR, but in the long run it will fail binary rank tests, too. The
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* other bits have no LFSR artifacts.
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*
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* We suggest to use a sign test to extract a random Boolean value, and
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* right shifts to extract subsets of bits.
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*
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* Note that the generator uses a simulated rotate operation, which most C
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* compilers will turn into a single instruction. In Java, you can use
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* Long.rotateLeft(). In languages that do not make low-level rotation
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* instructions accessible xorshift128+ could be faster.
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*
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* The state must be seeded so that it is not everywhere zero. If you have
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* a 64-bit seed, we suggest to seed a splitmix64 generator and use its
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* output to fill s.
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*/
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#include <init.h>
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#include <device.h>
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#include <drivers/entropy.h>
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#include <kernel.h>
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#include <string.h>
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static uint64_t state[2];
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static inline uint64_t rotl(const uint64_t x, int k)
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{
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return (x << k) | (x >> (64 - k));
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}
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static int xoroshiro128_initialize(struct device *dev)
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{
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dev = device_get_binding(DT_CHOSEN_ZEPHYR_ENTROPY_LABEL);
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if (!dev) {
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return -EINVAL;
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}
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int32_t rc = entropy_get_entropy_isr(dev, (uint8_t *)&state,
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sizeof(state), ENTROPY_BUSYWAIT);
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if (rc == -ENOTSUP) {
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/* Driver does not provide an ISR-specific API, assume it can
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* be called from ISR context
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*/
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rc = entropy_get_entropy(dev, (uint8_t *)&state, sizeof(state));
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}
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if (rc < 0) {
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return -EINVAL;
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}
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return 0;
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}
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static uint32_t xoroshiro128_next(void)
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{
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const uint64_t s0 = state[0];
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uint64_t s1 = state[1];
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const uint64_t result = s0 + s1;
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s1 ^= s0;
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state[0] = rotl(s0, 55) ^ s1 ^ (s1 << 14);
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state[1] = rotl(s1, 36);
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return (uint32_t)result;
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}
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uint32_t sys_rand32_get(void)
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{
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uint32_t ret;
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ret = xoroshiro128_next();
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return ret;
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}
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void sys_rand_get(void *dst, size_t outlen)
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{
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uint32_t ret;
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uint32_t blocksize = 4;
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uint32_t len = 0;
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uint32_t *udst = (uint32_t *)dst;
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while (len < outlen) {
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ret = xoroshiro128_next();
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if ((outlen-len) < sizeof(ret)) {
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blocksize = len;
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(void)memcpy(udst, &ret, blocksize);
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} else {
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(*udst++) = ret;
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}
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len += blocksize;
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}
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}
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/* In-tree entropy drivers will initialize in PRE_KERNEL_1; ensure that they're
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* initialized properly before initializing ourselves.
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*/
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SYS_INIT(xoroshiro128_initialize, PRE_KERNEL_2,
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CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);
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