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#include <linux/random.h>
14
15static inline u32 prandom_u32(void)
16{
17 return get_random_u32();
18}
19
20static inline void prandom_bytes(void *buf, size_t nbytes)
21{
22 return get_random_bytes(buf, nbytes);
23}
24
25struct rnd_state {
26 __u32 s1, s2, s3, s4;
27};
28
29u32 prandom_u32_state(struct rnd_state *state);
30void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
31void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
32
33#define prandom_init_once(pcpu_state) \
34 DO_ONCE(prandom_seed_full_state, (pcpu_state))
35
36/**
37 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
38 * @ep_ro: right open interval endpoint
39 *
40 * Returns a pseudo-random number that is in interval [0, ep_ro). Note
41 * that the result depends on PRNG being well distributed in [0, ~0U]
42 * u32 space. Here we use maximally equidistributed combined Tausworthe
43 * generator, that is, prandom_u32(). This is useful when requesting a
44 * random index of an array containing ep_ro elements, for example.
45 *
46 * Returns: pseudo-random number in interval [0, ep_ro)
47 */
48static inline u32 prandom_u32_max(u32 ep_ro)
49{
50 return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
51}
52
53/*
54 * Handle minimum values for seeds
55 */
56static inline u32 __seed(u32 x, u32 m)
57{
58 return (x < m) ? x + m : x;
59}
60
61/**
62 * prandom_seed_state - set seed for prandom_u32_state().
63 * @state: pointer to state structure to receive the seed.
64 * @seed: arbitrary 64-bit value to use as a seed.
65 */
66static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
67{
68 u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
69
70 state->s1 = __seed(i, 2U);
71 state->s2 = __seed(i, 8U);
72 state->s3 = __seed(i, 16U);
73 state->s4 = __seed(i, 128U);
74}
75
76/* Pseudo random number generator from numerical recipes. */
77static inline u32 next_pseudo_random32(u32 seed)
78{
79 return seed * 1664525 + 1013904223;
80}
81
82#endif
83

source code of linux/include/linux/prandom.h