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 */ 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 */ 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 */ 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. */ 70 static inline u32 next_pseudo_random32(u32 seed) 71 { 72 return seed * 1664525 + 1013904223; 73 } 74 75 #endif 76