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 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); 18 19 struct rnd_state { 20 __u32 s1, s2, s3, s4; 21 }; 22 23 DECLARE_PER_CPU(struct rnd_state, net_rand_state); 24 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); 28 29 #define prandom_init_once(pcpu_state) \ 30 DO_ONCE(prandom_seed_full_state, (pcpu_state)) 31 32 /** 33 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro) 34 * @ep_ro: right open interval endpoint 35 * 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. 41 * 42 * Returns: pseudo-random number in interval [0, ep_ro) 43 */ 44 static inline u32 prandom_u32_max(u32 ep_ro) 45 { 46 return (u32)(((u64) prandom_u32() * ep_ro) >> 32); 47 } 48 49 /* 50 * Handle minimum values for seeds 51 */ 52 static inline u32 __seed(u32 x, u32 m) 53 { 54 return (x < m) ? x + m : x; 55 } 56 57 /** 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. 61 */ 62 static inline void prandom_seed_state(struct rnd_state *state, u64 seed) 63 { 64 u32 i = (seed >> 32) ^ (seed << 10) ^ seed; 65 66 state->s1 = __seed(i, 2U); 67 state->s2 = __seed(i, 8U); 68 state->s3 = __seed(i, 16U); 69 state->s4 = __seed(i, 128U); 70 } 71 72 /* Pseudo random number generator from numerical recipes. */ 73 static inline u32 next_pseudo_random32(u32 seed) 74 { 75 return seed * 1664525 + 1013904223; 76 } 77 78 #endif 79