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>
15 /* Deprecated: use get_random_u32 instead. */
16 static inline u32 prandom_u32(void)
18 return get_random_u32();
21 /* Deprecated: use get_random_bytes instead. */
22 static inline void prandom_bytes(void *buf, size_t nbytes)
24 return get_random_bytes(buf, nbytes);
31 u32 prandom_u32_state(struct rnd_state *state);
32 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
33 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
35 #define prandom_init_once(pcpu_state) \
36 DO_ONCE(prandom_seed_full_state, (pcpu_state))
39 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
40 * @ep_ro: right open interval endpoint
42 * Returns a pseudo-random number that is in interval [0, ep_ro). This is
43 * useful when requesting a random index of an array containing ep_ro elements,
44 * for example. The result is somewhat biased when ep_ro is not a power of 2,
45 * so do not use this for cryptographic purposes.
47 * Returns: pseudo-random number in interval [0, ep_ro)
49 static inline u32 prandom_u32_max(u32 ep_ro)
51 if (__builtin_constant_p(ep_ro <= 1U << 8) && ep_ro <= 1U << 8)
52 return (get_random_u8() * ep_ro) >> 8;
53 if (__builtin_constant_p(ep_ro <= 1U << 16) && ep_ro <= 1U << 16)
54 return (get_random_u16() * ep_ro) >> 16;
55 return ((u64)get_random_u32() * ep_ro) >> 32;
59 * Handle minimum values for seeds
61 static inline u32 __seed(u32 x, u32 m)
63 return (x < m) ? x + m : x;
67 * prandom_seed_state - set seed for prandom_u32_state().
68 * @state: pointer to state structure to receive the seed.
69 * @seed: arbitrary 64-bit value to use as a seed.
71 static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
73 u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
75 state->s1 = __seed(i, 2U);
76 state->s2 = __seed(i, 8U);
77 state->s3 = __seed(i, 16U);
78 state->s4 = __seed(i, 128U);
81 /* Pseudo random number generator from numerical recipes. */
82 static inline u32 next_pseudo_random32(u32 seed)
84 return seed * 1664525 + 1013904223;