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>
13 #include <linux/random.h>
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);
23 #define prandom_init_once(pcpu_state) \
24 DO_ONCE(prandom_seed_full_state, (pcpu_state))
27 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
28 * @ep_ro: right open interval endpoint
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.
35 * Returns: pseudo-random number in interval [0, ep_ro)
37 static inline u32 prandom_u32_max(u32 ep_ro)
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;
47 * Handle minimum values for seeds
49 static inline u32 __seed(u32 x, u32 m)
51 return (x < m) ? x + m : x;
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.
59 static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
61 u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
63 state->s1 = __seed(i, 2U);
64 state->s2 = __seed(i, 8U);
65 state->s3 = __seed(i, 16U);
66 state->s4 = __seed(i, 128U);
69 /* Pseudo random number generator from numerical recipes. */
70 static inline u32 next_pseudo_random32(u32 seed)
72 return seed * 1664525 + 1013904223;