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/* SPDX-License-Identifier: GPL-2.0 */
/*
* include/linux/prandom.h
*
* Include file for the fast pseudo-random 32-bit
* generation.
*/
#ifndef _LINUX_PRANDOM_H
#define _LINUX_PRANDOM_H
#include <linux/types.h>
#include <linux/percpu.h>
#include <linux/random.h>
struct rnd_state {
__u32 s1, s2, s3, s4;
};
u32 prandom_u32_state(struct rnd_state *state);
void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
#define prandom_init_once(pcpu_state) \
DO_ONCE(prandom_seed_full_state, (pcpu_state))
/**
* prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
* @ep_ro: right open interval endpoint
*
* Returns a pseudo-random number that is in interval [0, ep_ro). This is
* useful when requesting a random index of an array containing ep_ro elements,
* for example. The result is somewhat biased when ep_ro is not a power of 2,
* so do not use this for cryptographic purposes.
*
* Returns: pseudo-random number in interval [0, ep_ro)
*/
static inline u32 prandom_u32_max(u32 ep_ro)
{
if (__builtin_constant_p(ep_ro <= 1U << 8) && ep_ro <= 1U << 8)
return (get_random_u8() * ep_ro) >> 8;
if (__builtin_constant_p(ep_ro <= 1U << 16) && ep_ro <= 1U << 16)
return (get_random_u16() * ep_ro) >> 16;
return ((u64)get_random_u32() * ep_ro) >> 32;
}
/*
* Handle minimum values for seeds
*/
static inline u32 __seed(u32 x, u32 m)
{
return (x < m) ? x + m : x;
}
/**
* prandom_seed_state - set seed for prandom_u32_state().
* @state: pointer to state structure to receive the seed.
* @seed: arbitrary 64-bit value to use as a seed.
*/
static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
{
u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
state->s1 = __seed(i, 2U);
state->s2 = __seed(i, 8U);
state->s3 = __seed(i, 16U);
state->s4 = __seed(i, 128U);
}
/* Pseudo random number generator from numerical recipes. */
static inline u32 next_pseudo_random32(u32 seed)
{
return seed * 1664525 + 1013904223;
}
#endif
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