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Split arc4random_uniform into it's own file and sync with OpenBSD.

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PR:		182610
Obtained from:	OpenBSD
MFC after:	2 weeks
This commit is contained in:
Xin LI 2018-08-18 06:20:45 +00:00
parent e7e0844422
commit 718863d076
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=337997
3 changed files with 59 additions and 35 deletions
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1
lib/libc/gen/Makefile.inc
View File

@ -16,6 +16,7 @@ SRCS+= __getosreldate.c \
_thread_init.c \
alarm.c \
arc4random.c \
arc4random_uniform.c \
assert.c \
auxv.c \
basename.c \

35
lib/libc/gen/arc4random.c
View File

@ -244,41 +244,6 @@ arc4random_buf(void *_buf, size_t n)
_ARC4_UNLOCK();
}
/*
* 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.
*/
u_int32_t
arc4random_uniform(u_int32_t upper_bound)
{
u_int32_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;
}
#if 0
/*-------- Test code for i386 --------*/
#include <stdio.h>

58
lib/libc/gen/arc4random_uniform.c Normal file
View File

@ -0,0 +1,58 @@
/* $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.
*
* $FreeBSD$
*/
#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;
}