From ca33590b6af032bff57d9cc70455660466a654b2 Mon Sep 17 00:00:00 2001 From: Luca Boccassi Date: Mon, 19 Feb 2018 11:16:57 +0000 Subject: New upstream version 18.02 Change-Id: I89ed24cb2a49b78fe5be6970b99dd46c1499fcc3 Signed-off-by: Luca Boccassi --- lib/librte_eal/common/include/rte_reciprocal.h | 90 ++++++++++++++++++++++++++ 1 file changed, 90 insertions(+) create mode 100644 lib/librte_eal/common/include/rte_reciprocal.h (limited to 'lib/librte_eal/common/include/rte_reciprocal.h') diff --git a/lib/librte_eal/common/include/rte_reciprocal.h b/lib/librte_eal/common/include/rte_reciprocal.h new file mode 100644 index 00000000..3492c73b --- /dev/null +++ b/lib/librte_eal/common/include/rte_reciprocal.h @@ -0,0 +1,90 @@ +/* SPDX-License-Identifier: BSD-3-Clause + * Copyright(c) 2017 Cavium, Inc + */ +/* + * 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_ + +#include + +struct rte_reciprocal { + uint32_t m; + uint8_t sh1, sh2; +}; + +struct rte_reciprocal_u64 { + uint64_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; +} + +static __rte_always_inline uint64_t +mullhi_u64(uint64_t x, uint64_t y) +{ +#ifdef __SIZEOF_INT128__ + __uint128_t xl = x; + __uint128_t rl = xl * y; + + return (rl >> 64); +#else + uint64_t u0, u1, v0, v1, k, t; + uint64_t w1, w2; + uint64_t whi; + + u1 = x >> 32; u0 = x & 0xFFFFFFFF; + v1 = y >> 32; v0 = y & 0xFFFFFFFF; + + t = u0*v0; + k = t >> 32; + + t = u1*v0 + k; + w1 = t & 0xFFFFFFFF; + w2 = t >> 32; + + t = u0*v1 + w1; + k = t >> 32; + + whi = u1*v1 + w2 + k; + + return whi; +#endif +} + +static __rte_always_inline uint64_t +rte_reciprocal_divide_u64(uint64_t a, struct rte_reciprocal_u64 *R) +{ + uint64_t t = mullhi_u64(a, R->m); + + return (t + ((a - t) >> R->sh1)) >> R->sh2; +} + +struct rte_reciprocal rte_reciprocal_value(uint32_t d); +struct rte_reciprocal_u64 rte_reciprocal_value_u64(uint64_t d); + +#endif /* _RTE_RECIPROCAL_H_ */ -- cgit 1.2.3-korg