The PIE code and other applications can benefit from having a fast way to get a random floating point value. This new function is equivalent to drand() in the standard library.
Signed-off-by: Stephen Hemminger <step...@networkplumber.org> Acked-by: Ray Kinsella <m...@ashoe.eu> --- app/test/test_rand_perf.c | 7 +++++++ doc/guides/rel_notes/release_22_07.rst | 5 +++++ lib/eal/common/rte_random.c | 19 +++++++++++++++++++ lib/eal/include/rte_random.h | 18 ++++++++++++++++++ lib/eal/version.map | 1 + 5 files changed, 50 insertions(+) diff --git a/app/test/test_rand_perf.c b/app/test/test_rand_perf.c index fe797ebfa1ca..26fb1d9a586e 100644 --- a/app/test/test_rand_perf.c +++ b/app/test/test_rand_perf.c @@ -20,6 +20,7 @@ static volatile uint64_t vsum; enum rand_type { rand_type_64, + rand_type_float, rand_type_bounded_best_case, rand_type_bounded_worst_case }; @@ -30,6 +31,8 @@ rand_type_desc(enum rand_type rand_type) switch (rand_type) { case rand_type_64: return "Full 64-bit [rte_rand()]"; + case rand_type_float: + return "Floating point [rte_drand()]"; case rand_type_bounded_best_case: return "Bounded average best-case [rte_rand_max()]"; case rand_type_bounded_worst_case: @@ -55,6 +58,9 @@ test_rand_perf_type(enum rand_type rand_type) case rand_type_64: sum += rte_rand(); break; + case rand_type_float: + sum += 1000. * rte_drand(); + break; case rand_type_bounded_best_case: sum += rte_rand_max(BEST_CASE_BOUND); break; @@ -83,6 +89,7 @@ test_rand_perf(void) printf("Pseudo-random number generation latencies:\n"); test_rand_perf_type(rand_type_64); + test_rand_perf_type(rand_type_float); test_rand_perf_type(rand_type_bounded_best_case); test_rand_perf_type(rand_type_bounded_worst_case); diff --git a/doc/guides/rel_notes/release_22_07.rst b/doc/guides/rel_notes/release_22_07.rst index e49cacecefd4..b131ea577226 100644 --- a/doc/guides/rel_notes/release_22_07.rst +++ b/doc/guides/rel_notes/release_22_07.rst @@ -104,6 +104,11 @@ New Features * ``RTE_EVENT_QUEUE_ATTR_WEIGHT`` * ``RTE_EVENT_QUEUE_ATTR_AFFINITY`` +* ** Added function get random floating point number.** + + Added the function ``rte_drand()`` to provide a pseudo-random + floating point number. + Removed Items ------------- diff --git a/lib/eal/common/rte_random.c b/lib/eal/common/rte_random.c index 4535cc980cec..166b0d8921c9 100644 --- a/lib/eal/common/rte_random.c +++ b/lib/eal/common/rte_random.c @@ -173,6 +173,25 @@ rte_rand_max(uint64_t upper_bound) return res; } +double +rte_drand(void) +{ + static const uint64_t denom = (uint64_t)1 << 53; + uint64_t rand64 = rte_rand(); + + /* + * The double mantissa only has 53 bits, so we uniformly mask off the + * high 11 bits and then floating-point divide by 2^53 to achieve a + * result in [0, 1). + * + * We are not allowed to emit 1.0, so denom must be one greater than + * the possible range of the preceding step. + */ + + rand64 &= denom - 1; + return (double)rand64 / denom; +} + static uint64_t __rte_random_initial_seed(void) { diff --git a/lib/eal/include/rte_random.h b/lib/eal/include/rte_random.h index 29f5f1325a30..f6541c2b0f08 100644 --- a/lib/eal/include/rte_random.h +++ b/lib/eal/include/rte_random.h @@ -65,6 +65,24 @@ rte_rand(void); uint64_t rte_rand_max(uint64_t upper_bound); +/** + * @warning + * @b EXPERIMENTAL: this API may change without prior notice + * + * Generates a pseudo-random floating point number. + * + * This function returns a nonnegative double-precision floating random + * number uniformly distributed over the interval [0.0, 1.0). + * + * The generator is not cryptographically secure. + * If called from lcore threads, this function is thread-safe. + * + * @return + * A pseudo-random value between 0 and 1.0. + */ +__rte_experimental +double rte_drand(void); + #ifdef __cplusplus } #endif diff --git a/lib/eal/version.map b/lib/eal/version.map index d49e30bd042f..cfbade9a33e9 100644 --- a/lib/eal/version.map +++ b/lib/eal/version.map @@ -422,6 +422,7 @@ EXPERIMENTAL { rte_intr_type_set; # added in 22.07 + rte_drand; rte_thread_get_affinity_by_id; rte_thread_self; rte_thread_set_affinity_by_id; -- 2.35.1