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 
prandom_u32(void)15 static inline u32 prandom_u32(void)
16 {
17 	return get_random_u32();
18 }
19 
prandom_bytes(void * buf,size_t nbytes)20 static inline void prandom_bytes(void *buf, size_t nbytes)
21 {
22 	return get_random_bytes(buf, nbytes);
23 }
24 
25 struct rnd_state {
26 	__u32 s1, s2, s3, s4;
27 };
28 
29 u32 prandom_u32_state(struct rnd_state *state);
30 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
31 void 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  */
prandom_u32_max(u32 ep_ro)48 static 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  */
__seed(u32 x,u32 m)56 static 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  */
prandom_seed_state(struct rnd_state * state,u64 seed)66 static 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. */
next_pseudo_random32(u32 seed)77 static inline u32 next_pseudo_random32(u32 seed)
78 {
79 	return seed * 1664525 + 1013904223;
80 }
81 
82 #endif
83