1 /* SPDX-License-Identifier: GPL-2.0 */
3 * include/linux/prandom.h
5 * Include file for the fast pseudo-random 32-bit
8 #ifndef _LINUX_PRANDOM_H
9 #define _LINUX_PRANDOM_H
11 #include <linux/types.h>
12 #include <linux/percpu.h>
14 u32 prandom_u32(void);
15 void prandom_bytes(void *buf, size_t nbytes);
16 void prandom_seed(u32 seed);
17 void prandom_reseed_late(void);
23 DECLARE_PER_CPU(struct rnd_state, net_rand_state);
25 u32 prandom_u32_state(struct rnd_state *state);
26 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
27 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
29 #define prandom_init_once(pcpu_state) \
30 DO_ONCE(prandom_seed_full_state, (pcpu_state))
33 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
34 * @ep_ro: right open interval endpoint
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.
42 * Returns: pseudo-random number in interval [0, ep_ro)
44 static inline u32 prandom_u32_max(u32 ep_ro)
46 return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
50 * Handle minimum values for seeds
52 static inline u32 __seed(u32 x, u32 m)
54 return (x < m) ? x + m : x;
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.
62 static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
64 u32 i = (seed >> 32) ^ (seed << 10) ^ seed;
66 state->s1 = __seed(i, 2U);
67 state->s2 = __seed(i, 8U);
68 state->s3 = __seed(i, 16U);
69 state->s4 = __seed(i, 128U);
72 /* Pseudo random number generator from numerical recipes. */
73 static inline u32 next_pseudo_random32(u32 seed)
75 return seed * 1664525 + 1013904223;