ceph/src/dpdk/lib/librte_sched/rte_reciprocal.c

   1 /*-
   2  *   BSD LICENSE
   3  *
   4  *   Copyright(c) Hannes Frederic Sowa
   5  *   All rights reserved.
   6  *
   7  *   Redistribution and use in source and binary forms, with or without
   8  *   modification, are permitted provided that the following conditions
   9  *   are met:
  10  *
  11  *     * Redistributions of source code must retain the above copyright
  12  *       notice, this list of conditions and the following disclaimer.
  13  *     * Redistributions in binary form must reproduce the above copyright
  14  *       notice, this list of conditions and the following disclaimer in
  15  *       the documentation and/or other materials provided with the
  16  *       distribution.
  17  *     * Neither the name of Intel Corporation nor the names of its
  18  *       contributors may be used to endorse or promote products derived
  19  *       from this software without specific prior written permission.
  20  *
  21  *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  24  *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  25  *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  26  *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  27  *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  28  *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  29  *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  30  *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  31  *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  32  */
  33
  34 #include <stdio.h>
  35 #include <stdint.h>
  36
  37 #include <rte_common.h>
  38
  39 #include "rte_reciprocal.h"
  40
  41 /* find largest set bit.
  42  * portable and slow but does not matter for this usage.
  43  */
  44 static inline int fls(uint32_t x)
  45 {
  46         int b;
  47
  48         for (b = 31; b >= 0; --b) {
  49                 if (x & (1u << b))
  50                         return b + 1;
  51         }
  52
  53         return 0;
  54 }
  55
  56 struct rte_reciprocal rte_reciprocal_value(uint32_t d)
  57 {
  58         struct rte_reciprocal R;
  59         uint64_t m;
  60         int l;
  61
  62         l = fls(d - 1);
  63         m = ((1ULL << 32) * ((1ULL << l) - d));
  64         m /= d;
  65
  66         ++m;
  67         R.m = m;
  68         R.sh1 = RTE_MIN(l, 1);
  69         R.sh2 = RTE_MAX(l - 1, 0);
  70
  71         return R;
  72 }