1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
/* $OpenBSD: arc4random_uniform.c,v 1.2 2015/09/13 08:31:47 guenther Exp $ */
/*
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
// This is arc4random_uniform.c from OpenBSD's source tree at
// $OPENBSD_ROOT/lib/libc/crypt/arc4random_uniform.c.
//
// Mumble-specific changes:
//
// - Change file extension to .cpp and rename to mumble_arc4random_uniform.cpp.
// - Add CryptographicRandom.h include.
// - Remove <sys/types.h> and <stdlib.h> includes, include <stdint.h> for uint32_t.
// - Added an implementation of arc4random called mumble_arc4random.
// - Rename arc4random_uniform to mumble_arc4random_uniform.
// - Change call to arc4random in mumble_arc4random_uniform to call
// mumble_arc4random instead of arc4random.
// - Remove DEF_WEAK for arc4random_uniform.
// - Disable MSVC warning 4146.
#include <stdint.h>
#include "CryptographicRandom.h"
#if defined(_MSC_VER)
// Disable "unary minus operator applied to unsigned type, result still unsigned"
// warning. The unary minus operator used in arc4random_uniform is perfectly valid.
# pragma warning(disable: 4146)
#endif
// Call through to CryptographicRandom::uint32()
uint32_t
mumble_arc4random(void)
{
return CryptographicRandom::uint32();
}
/*
* Calculate a uniformly distributed random number less than upper_bound
* avoiding "modulo bias".
*
* Uniformity is achieved by generating new random numbers until the one
* returned is outside the range [0, 2**32 % upper_bound). This
* guarantees the selected random number will be inside
* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
* after reduction modulo upper_bound.
*/
uint32_t
mumble_arc4random_uniform(uint32_t upper_bound)
{
uint32_t r, min;
if (upper_bound < 2)
return 0;
/* 2**32 % x == (2**32 - x) % x */
min = -upper_bound % upper_bound;
/*
* This could theoretically loop forever but each retry has
* p > 0.5 (worst case, usually far better) of selecting a
* number inside the range we need, so it should rarely need
* to re-roll.
*/
for (;;) {
r = mumble_arc4random();
if (r >= min)
break;
}
return r % upper_bound;
}
|
