/src/pdns/pdns/dnsdistdist/dns_random.hh
Line | Count | Source (jump to first uncovered line) |
1 | | /* |
2 | | * This file is part of PowerDNS or dnsdist. |
3 | | * Copyright -- PowerDNS.COM B.V. and its contributors |
4 | | * |
5 | | * This program is free software; you can redistribute it and/or modify |
6 | | * it under the terms of version 2 of the GNU General Public License as |
7 | | * published by the Free Software Foundation. |
8 | | * |
9 | | * In addition, for the avoidance of any doubt, permission is granted to |
10 | | * link this program with OpenSSL and to (re)distribute the binaries |
11 | | * produced as the result of such linking. |
12 | | * |
13 | | * This program is distributed in the hope that it will be useful, |
14 | | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
15 | | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
16 | | * GNU General Public License for more details. |
17 | | * |
18 | | * You should have received a copy of the GNU General Public License |
19 | | * along with this program; if not, write to the Free Software |
20 | | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
21 | | */ |
22 | | #pragma once |
23 | | #include <cstdint> |
24 | | #include <limits> |
25 | | #include <string> |
26 | | |
27 | | #include <ext/arc4random/arc4random.hh> |
28 | | |
29 | | inline uint32_t dns_random(uint32_t upper_bound) |
30 | 0 | { |
31 | 0 | return arc4random_uniform(upper_bound); |
32 | 0 | } |
33 | | |
34 | | inline uint32_t dns_random_uint32() |
35 | 0 | { |
36 | 0 | return arc4random(); |
37 | 0 | } |
38 | | |
39 | | inline uint16_t dns_random_uint16() |
40 | 0 | { |
41 | 0 | return arc4random() & 0xffff; |
42 | 0 | } |
43 | | |
44 | | namespace pdns |
45 | | { |
46 | | struct dns_random_engine |
47 | | { |
48 | | |
49 | | using result_type = uint32_t; |
50 | | |
51 | | static constexpr result_type min() |
52 | 0 | { |
53 | 0 | return 0; |
54 | 0 | } |
55 | | |
56 | | static constexpr result_type max() |
57 | 0 | { |
58 | 0 | return std::numeric_limits<result_type>::max(); |
59 | 0 | } |
60 | | |
61 | | result_type operator()() |
62 | 0 | { |
63 | 0 | return dns_random_uint32(); |
64 | 0 | } |
65 | | }; |
66 | | |
67 | | /* minimum value that a PRNG should return for this upper bound to avoid a modulo bias */ |
68 | | inline unsigned int random_minimum_acceptable_value(uint32_t upper_bound) |
69 | 0 | { |
70 | 0 | /* Parts of this code come from arc4random_uniform */ |
71 | 0 | /* To avoid "modulo bias" for some methods, calculate |
72 | 0 | minimum acceptable value for random number to improve |
73 | 0 | uniformity. |
74 | 0 |
|
75 | 0 | On applicable rngs, we loop until the rng spews out |
76 | 0 | value larger than min, and then take modulo out of that. |
77 | 0 | */ |
78 | 0 | unsigned int min = 0; |
79 | 0 | #if (ULONG_MAX > 0xffffffffUL) |
80 | 0 | min = 0x100000000UL % upper_bound; |
81 | 0 | #else |
82 | 0 | /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ |
83 | 0 | if (upper_bound > 0x80000000) |
84 | 0 | min = 1 + ~upper_bound; /* 2**32 - upper_bound */ |
85 | 0 | else { |
86 | 0 | /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ |
87 | 0 | min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; |
88 | 0 | } |
89 | 0 | #endif |
90 | 0 | return min; |
91 | 0 | } |
92 | | } |