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GCC Code Coverage Report

Directory:	./		Exec	Total	Coverage
File:	lib/libc/crypt/arc4random_uniform.c	Lines:	7	8	87.5 %
Date:	2017-11-13	Branches:	2	4	50.0 %


/*	$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.
 */

#include <sys/types.h>
#include <stdlib.h>

/*
 * 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
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 = arc4random();
		if (r >= min)
			break;
	}

	return r % upper_bound;
}
DEF_WEAK(arc4random_uniform);


Generated by: GCOVR (Version 3.3)

Line	Branch	Exec	Source
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			* [232 % upper_bound, 232) 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	✗✓	30	if (upper_bound < 2)
38			return 0;
39
40			/* 232 % x == (232 - x) % x */
41		15	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		15	for (;;) {
50		15	r = arc4random();
51	✗✓	15	if (r >= min)
52			break;
53			}
54
55		15	return r % upper_bound;
56		15	}
57			DEF_WEAK(arc4random_uniform);