ffe3ec811e
This adds (with permission of the original author) reciprocal divide based on algorithm in Linux. Signed-off-by: Stephen Hemminger <stephen@networkplumber.org> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
73 lines
2.2 KiB
C
73 lines
2.2 KiB
C
/*-
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* BSD LICENSE
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*
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* Copyright(c) Hannes Frederic Sowa
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* * Neither the name of Intel Corporation nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <stdio.h>
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#include <stdint.h>
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#include <rte_common.h>
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#include "rte_reciprocal.h"
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/* find largest set bit.
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* portable and slow but does not matter for this usage.
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*/
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static inline int fls(uint32_t x)
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{
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int b;
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for (b = 31; b >= 0; --b) {
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if (x & (1u << b))
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return b + 1;
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}
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return 0;
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}
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struct rte_reciprocal rte_reciprocal_value(uint32_t d)
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{
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struct rte_reciprocal R;
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uint64_t m;
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int l;
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l = fls(d - 1);
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m = ((1ULL << 32) * ((1ULL << l) - d));
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m /= d;
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++m;
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R.m = m;
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R.sh1 = RTE_MIN(l, 1);
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R.sh2 = RTE_MAX(l - 1, 0);
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return R;
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}
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