1 /*
2 * Copyright (C) 2003 Sean Chittenden <seanc@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 #ifndef __RANDOMIZE_FD__
28 #define __RANDOMIZE_FD__
29
30 #define RANDOM_TYPE_UNSET 0
31 #define RANDOM_TYPE_LINES 1
32 #define RANDOM_TYPE_WORDS 2
33
34 /* The multiple instance single integer key */
35 struct rand_node {
36 u_char *cp;
37 u_int len;
38 struct rand_node *next;
39 };
40
41 int randomize_fd(int fd, int type, int unique, double denom);
42
43 /*
44 * Generates a random number uniformly in the range [0.0, 1.0).
45 */
46 static inline double
random_unit_float(void)47 random_unit_float(void)
48 {
49 static const uint64_t denom = (1ull << 53);
50 static const uint64_t mask = denom - 1;
51
52 uint64_t rand64;
53
54 /*
55 * arc4random_buf(...) in this use generates integer outputs in [0,
56 * UINT64_MAX].
57 *
58 * The double mantissa only has 53 bits, so we uniformly mask off the
59 * high 11 bits and then floating-point divide by 2^53 to achieve a
60 * result in [0, 1).
61 *
62 * We are not allowed to emit 1.0, so denom must be one greater than
63 * the possible range of the preceeding step.
64 */
65 arc4random_buf(&rand64, sizeof(rand64));
66 rand64 &= mask;
67 return ((double)rand64 / denom);
68 }
69
70 /*
71 * Returns true with probability 1 / denom (a floating point number >= 1).
72 * Otherwise, returns false.
73 */
74 static inline bool
random_uniform_denom(double denom)75 random_uniform_denom(double denom)
76 {
77 return ((uint64_t)(denom * random_unit_float()) == 0);
78 }
79 #endif
80