From 5129044dce1f85ce4950f31bcf90f3886466f06a Mon Sep 17 00:00:00 2001 From: "C.J. Collier" Date: Tue, 14 Jun 2016 07:54:47 -0700 Subject: Imported upstream release 16.04 * gbp import-orig ../dpdk-16.04.tar.xz Change-Id: Iac2196db782ba322f6974d8a752acc34ce5024c3 Signed-off-by: C.J. Collier --- lib/librte_sched/rte_reciprocal.h | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 lib/librte_sched/rte_reciprocal.h (limited to 'lib/librte_sched/rte_reciprocal.h') diff --git a/lib/librte_sched/rte_reciprocal.h b/lib/librte_sched/rte_reciprocal.h new file mode 100644 index 00000000..abd15251 --- /dev/null +++ b/lib/librte_sched/rte_reciprocal.h @@ -0,0 +1,39 @@ +/* + * Reciprocal divide + * + * Used with permission from original authors + * Hannes Frederic Sowa and Daniel Borkmann + * + * This algorithm is based on the paper "Division by Invariant + * Integers Using Multiplication" by Torbjörn Granlund and Peter + * L. Montgomery. + * + * The assembler implementation from Agner Fog, which this code is + * based on, can be found here: + * http://www.agner.org/optimize/asmlib.zip + * + * This optimization for A/B is helpful if the divisor B is mostly + * runtime invariant. The reciprocal of B is calculated in the + * slow-path with reciprocal_value(). The fast-path can then just use + * a much faster multiplication operation with a variable dividend A + * to calculate the division A/B. + */ + +#ifndef _RTE_RECIPROCAL_H_ +#define _RTE_RECIPROCAL_H_ + +struct rte_reciprocal { + uint32_t m; + uint8_t sh1, sh2; +}; + +static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R) +{ + uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32); + + return (t + ((a - t) >> R.sh1)) >> R.sh2; +} + +struct rte_reciprocal rte_reciprocal_value(uint32_t d); + +#endif /* _RTE_RECIPROCAL_H_ */ -- cgit 1.2.3-korg