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get_random_u32_below()

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Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-06-27 19:45:40 -04:00
parent cfa816bf3f
commit 619c99de4b
1 changed files with 24 additions and 0 deletions
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24
include/linux/random.h
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@ -9,6 +9,7 @@
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/bug.h>
#include <linux/log2.h>
#ifdef SYS_getrandom
static inline int getrandom(void *buf, size_t buflen, unsigned int flags)
@ -40,7 +41,30 @@ static inline type get_random_##type(void) \
get_random_type(int);
get_random_type(long);
get_random_type(u8);
get_random_type(u16);
get_random_type(u32);
get_random_type(u64);
static inline u32 get_random_u32_below(u32 ceil)
{
if (ceil <= 1)
return 0;
for (;;) {
if (ceil <= 1U << 8) {
u32 mult = ceil * get_random_u8();
if (likely(is_power_of_2(ceil) || (u8)mult >= (1U << 8) % ceil))
return mult >> 8;
} else if (ceil <= 1U << 16) {
u32 mult = ceil * get_random_u16();
if (likely(is_power_of_2(ceil) || (u16)mult >= (1U << 16) % ceil))
return mult >> 16;
} else {
u64 mult = (u64)ceil * get_random_u32();
if (likely(is_power_of_2(ceil) || (u32)mult >= -ceil % ceil))
return mult >> 32;
}
}
}
#endif /* _LINUX_RANDOM_H */