Absolute File Name: | /home/opencoverage/opencoverage/guest-scripts/libressl/src/crypto/compat/arc4random_uniform.c |
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1 | /* $OpenBSD: arc4random_uniform.c,v 1.2 2015/09/13 08:31:47 guenther Exp $ */ | - | ||||||
2 | - | |||||||
3 | /* | - | ||||||
4 | * Copyright (c) 2008, Damien Miller <djm@openbsd.org> | - | ||||||
5 | * | - | ||||||
6 | * Permission to use, copy, modify, and distribute this software for any | - | ||||||
7 | * purpose with or without fee is hereby granted, provided that the above | - | ||||||
8 | * copyright notice and this permission notice appear in all copies. | - | ||||||
9 | * | - | ||||||
10 | * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES | - | ||||||
11 | * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF | - | ||||||
12 | * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR | - | ||||||
13 | * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES | - | ||||||
14 | * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN | - | ||||||
15 | * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF | - | ||||||
16 | * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. | - | ||||||
17 | */ | - | ||||||
18 | - | |||||||
19 | #include <sys/types.h> | - | ||||||
20 | #include <stdlib.h> | - | ||||||
21 | - | |||||||
22 | /* | - | ||||||
23 | * Calculate a uniformly distributed random number less than upper_bound | - | ||||||
24 | * avoiding "modulo bias". | - | ||||||
25 | * | - | ||||||
26 | * Uniformity is achieved by generating new random numbers until the one | - | ||||||
27 | * returned is outside the range [0, 2**32 % upper_bound). This | - | ||||||
28 | * guarantees the selected random number will be inside | - | ||||||
29 | * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) | - | ||||||
30 | * after reduction modulo upper_bound. | - | ||||||
31 | */ | - | ||||||
32 | uint32_t | - | ||||||
33 | arc4random_uniform(uint32_t upper_bound) | - | ||||||
34 | { | - | ||||||
35 | uint32_t r, min; | - | ||||||
36 | - | |||||||
37 | if (upper_bound < 2)
| 0 | ||||||
38 | return 0; never executed: return 0; | 0 | ||||||
39 | - | |||||||
40 | /* 2**32 % x == (2**32 - x) % x */ | - | ||||||
41 | min = -upper_bound % upper_bound; | - | ||||||
42 | - | |||||||
43 | /* | - | ||||||
44 | * This could theoretically loop forever but each retry has | - | ||||||
45 | * p > 0.5 (worst case, usually far better) of selecting a | - | ||||||
46 | * number inside the range we need, so it should rarely need | - | ||||||
47 | * to re-roll. | - | ||||||
48 | */ | - | ||||||
49 | for (;;) { | - | ||||||
50 | r = arc4random(); | - | ||||||
51 | if (r >= min)
| 0 | ||||||
52 | break; never executed: break; | 0 | ||||||
53 | } never executed: end of block | 0 | ||||||
54 | - | |||||||
55 | return r % upper_bound; never executed: return r % upper_bound; | 0 | ||||||
56 | } | - | ||||||
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