9c1e0dc39a
The EAL API (with doxygen documentation) is moved from common/include/ to include/, which makes more clear that it is the global API for all environments and architectures. Note that the arch-specific and OS-specific include files are not in this global include directory, but include/generic/ should cover the doxygen documentation for them. Signed-off-by: Thomas Monjalon <thomas@monjalon.net> Acked-by: David Marchand <david.marchand@redhat.com>
91 lines
2 KiB
C
91 lines
2 KiB
C
/* SPDX-License-Identifier: BSD-3-Clause
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* Copyright(c) 2017 Cavium, Inc
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*/
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/*
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* Reciprocal divide
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*
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* Used with permission from original authors
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* Hannes Frederic Sowa and Daniel Borkmann
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*
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* This algorithm is based on the paper "Division by Invariant
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* Integers Using Multiplication" by Torbjörn Granlund and Peter
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* L. Montgomery.
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*
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* The assembler implementation from Agner Fog, which this code is
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* based on, can be found here:
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* http://www.agner.org/optimize/asmlib.zip
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*
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* This optimization for A/B is helpful if the divisor B is mostly
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* runtime invariant. The reciprocal of B is calculated in the
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* slow-path with reciprocal_value(). The fast-path can then just use
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* a much faster multiplication operation with a variable dividend A
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* to calculate the division A/B.
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*/
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#ifndef _RTE_RECIPROCAL_H_
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#define _RTE_RECIPROCAL_H_
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#include <stdint.h>
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struct rte_reciprocal {
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uint32_t m;
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uint8_t sh1, sh2;
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};
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struct rte_reciprocal_u64 {
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uint64_t m;
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uint8_t sh1, sh2;
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};
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static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R)
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{
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uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32);
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return (t + ((a - t) >> R.sh1)) >> R.sh2;
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}
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static __rte_always_inline uint64_t
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mullhi_u64(uint64_t x, uint64_t y)
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{
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#ifdef __SIZEOF_INT128__
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__uint128_t xl = x;
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__uint128_t rl = xl * y;
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return (rl >> 64);
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#else
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uint64_t u0, u1, v0, v1, k, t;
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uint64_t w1, w2;
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uint64_t whi;
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u1 = x >> 32; u0 = x & 0xFFFFFFFF;
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v1 = y >> 32; v0 = y & 0xFFFFFFFF;
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t = u0*v0;
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k = t >> 32;
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t = u1*v0 + k;
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w1 = t & 0xFFFFFFFF;
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w2 = t >> 32;
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t = u0*v1 + w1;
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k = t >> 32;
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whi = u1*v1 + w2 + k;
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return whi;
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#endif
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}
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static __rte_always_inline uint64_t
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rte_reciprocal_divide_u64(uint64_t a, const struct rte_reciprocal_u64 *R)
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{
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uint64_t t = mullhi_u64(a, R->m);
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return (t + ((a - t) >> R->sh1)) >> R->sh2;
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}
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struct rte_reciprocal rte_reciprocal_value(uint32_t d);
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struct rte_reciprocal_u64 rte_reciprocal_value_u64(uint64_t d);
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#endif /* _RTE_RECIPROCAL_H_ */
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