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1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * include/linux/prandom.h
4 *
5 * Include file for the fast pseudo-random 32-bit
6 * generation.
7 */
8#ifndef _LINUX_PRANDOM_H
9#define _LINUX_PRANDOM_H
10
11#include <linux/types.h>
12#include <linux/percpu.h>
13
14u32 prandom_u32(void);
15void prandom_bytes(void *buf, size_t nbytes);
16void prandom_seed(u32 seed);
17void prandom_reseed_late(void);
18
19struct rnd_state {
20 __u32 s1, s2, s3, s4;
21};
22
23DECLARE_PER_CPU(struct rnd_state, net_rand_state);
24
25u32 prandom_u32_state(struct rnd_state *state);
26void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
27void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
28
29#define prandom_init_once(pcpu_state) \
30 DO_ONCE(prandom_seed_full_state, (pcpu_state))
31
32/**
33 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
34 * @ep_ro: right open interval endpoint
35 *
36 * Returns a pseudo-random number that is in interval [0, ep_ro). Note
37 * that the result depends on PRNG being well distributed in [0, ~0U]
38 * u32 space. Here we use maximally equidistributed combined Tausworthe
39 * generator, that is, prandom_u32(). This is useful when requesting a
40 * random index of an array containing ep_ro elements, for example.
41 *
42 * Returns: pseudo-random number in interval [0, ep_ro)
43 */
44static inline u32 prandom_u32_max(u32 ep_ro)
45{
46 return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
47}
48
49/*
50 * Handle minimum values for seeds
51 */
52static inline u32 __seed(u32 x, u32 m)
53{
54 return (x < m) ? x + m : x;
55}
56
57/**
58 * prandom_seed_state - set seed for prandom_u32_state().
59 * @state: pointer to state structure to receive the seed.
60 * @seed: arbitrary 64-bit value to use as a seed.
61 */
62static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
63{
64 u32 i = (seed >> 32) ^ (seed << 10) ^ seed;
65
66 state->s1 = __seed(i, 2U);
67 state->s2 = __seed(i, 8U);
68 state->s3 = __seed(i, 16U);
69 state->s4 = __seed(i, 128U);
70}
71
72/* Pseudo random number generator from numerical recipes. */
73static inline u32 next_pseudo_random32(u32 seed)
74{
75 return seed * 1664525 + 1013904223;
76}
77
78#endif