ceph/src/seastar/dpdk/lib/librte_eal/common/rte_reciprocal.c

   1 /* SPDX-License-Identifier: BSD-3-Clause
   2  * Copyright(c) 2017 Cavium, Inc
   3  */
   4 /*-
   5  *   BSD LICENSE
   6  *
   7  *   Copyright(c) Hannes Frederic Sowa
   8  *   All rights reserved.
   9  *
  10  *   Redistribution and use in source and binary forms, with or without
  11  *   modification, are permitted provided that the following conditions
  12  *   are met:
  13  *
  14  *     * Redistributions of source code must retain the above copyright
  15  *       notice, this list of conditions and the following disclaimer.
  16  *     * Redistributions in binary form must reproduce the above copyright
  17  *       notice, this list of conditions and the following disclaimer in
  18  *       the documentation and/or other materials provided with the
  19  *       distribution.
  20  *     * Neither the name of Intel Corporation nor the names of its
  21  *       contributors may be used to endorse or promote products derived
  22  *       from this software without specific prior written permission.
  23  *
  24  *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  25  *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  26  *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  27  *   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  28  *   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  29  *   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  30  *   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  31  *   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  32  *   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  33  *   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  34  *   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  35  */
  36
  37 #include <stdio.h>
  38 #include <stdint.h>
  39
  40 #include <rte_common.h>
  41
  42 #include "rte_reciprocal.h"
  43
  44 struct rte_reciprocal rte_reciprocal_value(uint32_t d)
  45 {
  46         struct rte_reciprocal R;
  47         uint64_t m;
  48         int l;
  49
  50         l = rte_fls_u32(d - 1);
  51         m = ((1ULL << 32) * ((1ULL << l) - d));
  52         m /= d;
  53
  54         ++m;
  55         R.m = m;
  56         R.sh1 = RTE_MIN(l, 1);
  57         R.sh2 = RTE_MAX(l - 1, 0);
  58
  59         return R;
  60 }
  61
  62 /*
  63  * Code taken from Hacker's Delight:
  64  * http://www.hackersdelight.org/hdcodetxt/divlu.c.txt
  65  * License permits inclusion here per:
  66  * http://www.hackersdelight.org/permissions.htm
  67  */
  68 static uint64_t
  69 divide_128_div_64_to_64(uint64_t u1, uint64_t u0, uint64_t v, uint64_t *r)
  70 {
  71         const uint64_t b = (1ULL << 32); /* Number base (16 bits). */
  72         uint64_t un1, un0,           /* Norm. dividend LSD's. */
  73                  vn1, vn0,           /* Norm. divisor digits. */
  74                  q1, q0,             /* Quotient digits. */
  75                  un64, un21, un10,   /* Dividend digit pairs. */
  76                  rhat;               /* A remainder. */
  77         int s;                       /* Shift amount for norm. */
  78
  79         /* If overflow, set rem. to an impossible value. */
  80         if (u1 >= v) {
  81                 if (r != NULL)
  82                         *r = (uint64_t) -1;
  83                 return (uint64_t) -1;
  84         }
  85
  86         /* Count leading zeros. */
  87         s = __builtin_clzll(v);
  88         if (s > 0) {
  89                 v = v << s;
  90                 un64 = (u1 << s) | ((u0 >> (64 - s)) & (-s >> 31));
  91                 un10 = u0 << s;
  92         } else {
  93
  94                 un64 = u1 | u0;
  95                 un10 = u0;
  96         }
  97
  98         vn1 = v >> 32;
  99         vn0 = v & 0xFFFFFFFF;
 100
 101         un1 = un10 >> 32;
 102         un0 = un10 & 0xFFFFFFFF;
 103
 104         q1 = un64/vn1;
 105         rhat = un64 - q1*vn1;
 106 again1:
 107         if (q1 >= b || q1*vn0 > b*rhat + un1) {
 108                 q1 = q1 - 1;
 109                 rhat = rhat + vn1;
 110                 if (rhat < b)
 111                         goto again1;
 112         }
 113
 114         un21 = un64*b + un1 - q1*v;
 115
 116         q0 = un21/vn1;
 117         rhat = un21 - q0*vn1;
 118 again2:
 119         if (q0 >= b || q0*vn0 > b*rhat + un0) {
 120                 q0 = q0 - 1;
 121                 rhat = rhat + vn1;
 122                 if (rhat < b)
 123                         goto again2;
 124         }
 125
 126         if (r != NULL)
 127                 *r = (un21*b + un0 - q0*v) >> s;
 128         return q1*b + q0;
 129 }
 130
 131 struct rte_reciprocal_u64
 132 rte_reciprocal_value_u64(uint64_t d)
 133 {
 134         struct rte_reciprocal_u64 R;
 135         uint64_t m;
 136         int l;
 137
 138         l = 63 - __builtin_clzll(d);
 139
 140         m = divide_128_div_64_to_64((1ULL << l), 0, d, NULL) << 1;
 141         m = (1ULL << l) - d ? m + 2 : 1;
 142         R.m = m;
 143
 144         R.sh1 = l > 1 ? 1 : l;
 145         R.sh2 = (l > 0) ? l : 0;
 146         R.sh2 -= R.sh2 && (m == 1) ? 1 : 0;
 147
 148         return R;
 149 }