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
15 struct rnd_state {
16 __u32 s1, s2, s3, s4;
17 };
18
19 u32 prandom_u32_state(struct rnd_state *state);
20 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
21 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
22
23 #define prandom_init_once(pcpu_state) \
24 DO_ONCE(prandom_seed_full_state, (pcpu_state))
25
26 /**
27 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
28 * @ep_ro: right open interval endpoint
29 *
30 * Returns a pseudo-random number that is in interval [0, ep_ro). This is
31 * useful when requesting a random index of an array containing ep_ro elements,
32 * for example. The result is somewhat biased when ep_ro is not a power of 2,
33 * so do not use this for cryptographic purposes.
34 *
35 * Returns: pseudo-random number in interval [0, ep_ro)
36 */
prandom_u32_max(u32 ep_ro)37 static inline u32 prandom_u32_max(u32 ep_ro)
38 {
39 if (__builtin_constant_p(ep_ro <= 1U << 8) && ep_ro <= 1U << 8)
40 return (get_random_u8() * ep_ro) >> 8;
41 if (__builtin_constant_p(ep_ro <= 1U << 16) && ep_ro <= 1U << 16)
42 return (get_random_u16() * ep_ro) >> 16;
43 return ((u64)get_random_u32() * ep_ro) >> 32;
44 }
45
46 /*
47 * Handle minimum values for seeds
48 */
__seed(u32 x,u32 m)49 static inline u32 __seed(u32 x, u32 m)
50 {
51 return (x < m) ? x + m : x;
52 }
53
54 /**
55 * prandom_seed_state - set seed for prandom_u32_state().
56 * @state: pointer to state structure to receive the seed.
57 * @seed: arbitrary 64-bit value to use as a seed.
58 */
prandom_seed_state(struct rnd_state * state,u64 seed)59 static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
60 {
61 u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
62
63 state->s1 = __seed(i, 2U);
64 state->s2 = __seed(i, 8U);
65 state->s3 = __seed(i, 16U);
66 state->s4 = __seed(i, 128U);
67 }
68
69 /* Pseudo random number generator from numerical recipes. */
next_pseudo_random32(u32 seed)70 static inline u32 next_pseudo_random32(u32 seed)
71 {
72 return seed * 1664525 + 1013904223;
73 }
74
75 #endif
76
