| Message ID | 1378298247-29364-2-git-send-email-dborkman@redhat.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 2013-09-04 at 14:37 +0200, Daniel Borkmann wrote: > We have implemented the same function over and over, so introduce > generic helpers that unify these implementations in order to migrate > such code to use them. Make the API similarly to randomize_range() > for consistency. prandom_u32_range() generates numbers in [start, end] > interval and prandom_u32_max() generates numbers in [0, end] interval. I think these helpers can in many cases cause poorer compiler generated object code. > +/** > + * prandom_u32_range - return a random number in interval [start, end] > + * @start: lower interval endpoint > + * @end: higher interval endpoint > + * > + * Returns a number that is in the given interval: > + * > + * [...... <range> .....] > + * start end > + * > + * Callers need to make sure that start <= end. Note that the result > + * depends on PRNG being well distributed in [0, ~0U] space. Here we > + * use maximally equidistributed combined Tausworthe generator. > + */ > +static inline u32 prandom_u32_range(u32 start, u32 end) > +{ > + return (u32)(((u64) prandom_u32() * (end + 1 - start)) >> 32) + start; > +} This is effectively: return (prandom_u32() % (end - start)) + start; and if start and end are constant, gcc can optimize the division by constant to a 32 bit multiply/shift/add. I think if you add __builtin_constant_p tests for start and end and expand the code a little you can still get the optimizations done. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/random.h b/include/linux/random.h index 3b9377d..17c91c2 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); @@ -32,6 +31,36 @@ void prandom_seed(u32 seed); u32 prandom_u32_state(struct rnd_state *); void prandom_bytes_state(struct rnd_state *state, void *buf, int nbytes); +/** + * prandom_u32_range - return a random number in interval [start, end] + * @start: lower interval endpoint + * @end: higher interval endpoint + * + * Returns a number that is in the given interval: + * + * [...... <range> .....] + * start end + * + * Callers need to make sure that start <= end. Note that the result + * depends on PRNG being well distributed in [0, ~0U] space. Here we + * use maximally equidistributed combined Tausworthe generator. + */ +static inline u32 prandom_u32_range(u32 start, u32 end) +{ + return (u32)(((u64) prandom_u32() * (end + 1 - start)) >> 32) + start; +} + +/** + * prandom_u32_max - return a random number in interval [0, max] + * @max: higher interval endpoint + * + * Returns a number that is in interval [0, end]. + */ +static inline u32 prandom_u32_max(u32 end) +{ + return prandom_u32_range(0, end); +} + /* * Handle minimum values for seeds */
We have implemented the same function over and over, so introduce generic helpers that unify these implementations in order to migrate such code to use them. Make the API similarly to randomize_range() for consistency. prandom_u32_range() generates numbers in [start, end] interval and prandom_u32_max() generates numbers in [0, end] interval. Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Joe Perches <joe@perches.com> Cc: linux-kernel@vger.kernel.org --- include/linux/random.h | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-)