Stephen Hemminger <step...@networkplumber.org> writes:
> 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 erand48_r in the standard library.
>
> Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
> ---
> app/test/test_rand_perf.c | 7 +++++++
> doc/guides/rel_notes/release_22_07.rst | 5 +++++
> lib/eal/common/rte_random.c | 21 +++++++++++++++++++++
> lib/eal/include/rte_random.h | 17 +++++++++++++++++
> lib/eal/version.map | 1 +
> 5 files changed, 51 insertions(+)
>
> diff --git a/app/test/test_rand_perf.c b/app/test/test_rand_perf.c
> index fe797ebfa1ca..f3602da5b2d4 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_rand_float()]";
> 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 += rte_rand_float() * UINT64_MAX;
> + 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..128d4fca85b3 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_rand_float()`` 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..024c3c41dc16 100644
> --- a/lib/eal/common/rte_random.c
> +++ b/lib/eal/common/rte_random.c
> @@ -6,6 +6,7 @@
> #include <x86intrin.h>
> #endif
> #include <unistd.h>
> +#include <ieee754.h>
>
> #include <rte_branch_prediction.h>
> #include <rte_cycles.h>
> @@ -173,6 +174,26 @@ rte_rand_max(uint64_t upper_bound)
> return res;
> }
>
> +double
> +rte_rand_float(void)
> +{
> + struct rte_rand_state *state = __rte_rand_get_state();
> + union ieee754_double u = {
> + .ieee = {
> + .negative = 0,
> + .exponent = IEEE754_DOUBLE_BIAS,
> + },
> + };
> + uint64_t val;
> +
> + /* Take 64 bit random value and put it into the mantissa */
> + val = __rte_rand_lfsr258(state);
> + u.ieee.mantissa0 = val >> 32; /* only 20 bits used */
> + u.ieee.mantissa1 = (uint32_t)val;
> +
> + return u.d - 1.0;
> +}
> +
> 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..553beb2d9c6f 100644
> --- a/lib/eal/include/rte_random.h
> +++ b/lib/eal/include/rte_random.h
> @@ -65,6 +65,23 @@ 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-precison floating random
> + * number uniformly distributed over the interval [0.0, 1.0).
> + *
> + * If called from lcore threads, this function is thread-safe.
> + *
> + * @return
> + * A pseudo-random value between 0 and 1.0.
> + */
> +__rte_experimental
> +double rte_rand_float(void);
> +
> #ifdef __cplusplus
> }
> #endif
> diff --git a/lib/eal/version.map b/lib/eal/version.map
> index d49e30bd042f..861906af2999 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_rand_float;
Niggle - is there an alignment issue on the line above?
> rte_thread_get_affinity_by_id;
> rte_thread_self;
> rte_thread_set_affinity_by_id;
--
Regards, Ray K
