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12471842 PL |
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 | */ | |
e8c59f2d | 22 | #pragma once |
a49c8752 | 23 | #include <cstdint> |
bbec1961 | 24 | #include <limits> |
f573af85 | 25 | #include <string> |
8a5d483e | 26 | |
a0d8a0f0 OM |
27 | #include <ext/arc4random/arc4random.hh> |
28 | ||
29 | inline uint32_t dns_random(uint32_t upper_bound) | |
30 | { | |
31 | return arc4random_uniform(upper_bound); | |
32 | } | |
33 | ||
34 | inline uint32_t dns_random_uint32() | |
35 | { | |
36 | return arc4random(); | |
37 | } | |
38 | ||
39 | inline uint16_t dns_random_uint16() | |
40 | { | |
41 | return arc4random() & 0xffff; | |
42 | } | |
bbec1961 | 43 | |
03544d6f OM |
44 | namespace pdns |
45 | { | |
46 | struct dns_random_engine | |
47 | { | |
bbec1961 | 48 | |
f777e801 | 49 | using result_type = uint32_t; |
bbec1961 | 50 | |
03544d6f OM |
51 | static constexpr result_type min() |
52 | { | |
53 | return 0; | |
54 | } | |
bbec1961 | 55 | |
03544d6f OM |
56 | static constexpr result_type max() |
57 | { | |
43159bf1 | 58 | return std::numeric_limits<result_type>::max(); |
03544d6f | 59 | } |
f573af85 | 60 | |
03544d6f | 61 | result_type operator()() |
f573af85 | 62 | { |
43159bf1 | 63 | return dns_random_uint32(); |
03544d6f OM |
64 | } |
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 | { | |
70 | /* Parts of this code come from arc4random_uniform */ | |
71 | /* To avoid "modulo bias" for some methods, calculate | |
72 | minimum acceptable value for random number to improve | |
73 | uniformity. | |
f573af85 | 74 | |
03544d6f OM |
75 | On applicable rngs, we loop until the rng spews out |
76 | value larger than min, and then take modulo out of that. | |
77 | */ | |
f777e801 | 78 | unsigned int min = 0; |
f573af85 | 79 | #if (ULONG_MAX > 0xffffffffUL) |
03544d6f | 80 | min = 0x100000000UL % upper_bound; |
f573af85 | 81 | #else |
03544d6f OM |
82 | /* Calculate (2**32 % upper_bound) avoiding 64-bit math */ |
83 | if (upper_bound > 0x80000000) | |
84 | min = 1 + ~upper_bound; /* 2**32 - upper_bound */ | |
85 | else { | |
86 | /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */ | |
87 | min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound; | |
f573af85 | 88 | } |
03544d6f OM |
89 | #endif |
90 | return min; | |
91 | } | |
bbec1961 | 92 | } |