summaryrefslogtreecommitdiffstats
path: root/include/linux/random.h
diff options
context:
space:
mode:
Diffstat (limited to 'include/linux/random.h')
-rw-r--r--include/linux/random.h18
1 files changed, 17 insertions, 1 deletions
diff --git a/include/linux/random.h b/include/linux/random.h
index 4002b3df4c8..1cfce0e24db 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -8,7 +8,6 @@
#include <uapi/linux/random.h>
-
extern void add_device_randomness(const void *, unsigned int);
extern void add_input_randomness(unsigned int type, unsigned int code,
unsigned int value);
@@ -38,6 +37,23 @@ struct rnd_state {
u32 prandom_u32_state(struct rnd_state *state);
void prandom_bytes_state(struct rnd_state *state, void *buf, int nbytes);
+/**
+ * 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). Note
+ * that the result depends on PRNG being well distributed in [0, ~0U]
+ * u32 space. Here we use maximally equidistributed combined Tausworthe
+ * generator, that is, prandom_u32(). This is useful when requesting a
+ * random index of an array containing ep_ro elements, for example.
+ *
+ * Returns: pseudo-random number in interval [0, ep_ro)
+ */
+static inline u32 prandom_u32_max(u32 ep_ro)
+{
+ return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
+}
+
/*
* Handle minimum values for seeds
*/