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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 | } |