blob: 26bd7b4856a126a26530dfa6c08a4a121ac0946e [file] [log] [blame]
/*
* Copyright (c) 2017 Intel Corporation
*
* SPDX-License-Identifier: CC0-1.0
*
* Based on code written in 2016 by David Blackman and Sebastiano Vigna
* (vigna@acm.org)
*
* To the extent possible under law, the author has dedicated all copyright
* and related and neighboring rights to this software to the public domain
* worldwide. This software is distributed without any warranty.
*
* See <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
/* This is the successor to xorshift128+. It is the fastest full-period
* generator passing BigCrush without systematic failures, but due to the
* relatively short period it is acceptable only for applications with a
* mild amount of parallelism; otherwise, use a xorshift1024* generator.
*
* Beside passing BigCrush, this generator passes the PractRand test suite
* up to (and included) 16TB, with the exception of binary rank tests, as
* the lowest bit of this generator is an LSFR. The next bit is not an
* LFSR, but in the long run it will fail binary rank tests, too. The
* other bits have no LFSR artifacts.
*
* We suggest to use a sign test to extract a random Boolean value, and
* right shifts to extract subsets of bits.
*
* Note that the generator uses a simulated rotate operation, which most C
* compilers will turn into a single instruction. In Java, you can use
* Long.rotateLeft(). In languages that do not make low-level rotation
* instructions accessible xorshift128+ could be faster.
*
* The state must be seeded so that it is not everywhere zero. If you have
* a 64-bit seed, we suggest to seed a splitmix64 generator and use its
* output to fill s.
*/
#include <init.h>
#include <device.h>
#include <entropy.h>
#include <kernel.h>
static u64_t state[2];
K_SEM_DEFINE(state_sem, 1, 1);
static inline u64_t rotl(const u64_t x, int k)
{
return (x << k) | (x >> (64 - k));
}
static int xoroshiro128_initialize(struct device *dev)
{
dev = device_get_binding(CONFIG_ENTROPY_NAME);
if (!dev) {
return -EINVAL;
}
if (entropy_get_entropy(dev, (uint8_t *)&state, sizeof(state)) < 0) {
return -EINVAL;
}
k_object_access_all_grant(&state_sem);
return 0;
}
static u32_t xoroshiro128_next(void)
{
const u64_t s0 = state[0];
u64_t s1 = state[1];
const u64_t result = s0 + s1;
s1 ^= s0;
state[0] = rotl(s0, 55) ^ s1 ^ (s1 << 14);
state[1] = rotl(s1, 36);
return (u32_t)result;
}
u32_t sys_rand32_get(void)
{
u32_t ret;
if (k_sem_take(&state_sem, K_FOREVER) < 0) {
/* FIXME: with all threads having access to this semaphore,
* it's possible that they can corrupt state_sem in a way
* that k_sem_take will fail. This can be abused to
* generate numbers without using the xoroshiro128+ RNG.
*/
return k_cycle_get_32();
}
ret = xoroshiro128_next();
k_sem_give(&state_sem);
return ret;
}
/* In-tree entropy drivers will initialize in PRE_KERNEL_1; ensure that they're
* initialized properly before initializing ourselves.
*/
SYS_INIT(xoroshiro128_initialize, PRE_KERNEL_2,
CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);