Split arc4random_uniform into it's own file and sync with OpenBSD.
PR: 182610 Obtained from: OpenBSD MFC after: 2 weeks
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=337997
@ -16,6 +16,7 @@ SRCS+= __getosreldate.c \
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_thread_init.c \
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alarm.c \
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arc4random.c \
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arc4random_uniform.c \
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assert.c \
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auxv.c \
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basename.c \
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@ -244,41 +244,6 @@ arc4random_buf(void *_buf, size_t n)
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_ARC4_UNLOCK();
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}
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/*
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* Calculate a uniformly distributed random number less than upper_bound
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* avoiding "modulo bias".
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*
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* Uniformity is achieved by generating new random numbers until the one
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* returned is outside the range [0, 2**32 % upper_bound). This
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* guarantees the selected random number will be inside
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* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
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* after reduction modulo upper_bound.
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*/
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u_int32_t
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arc4random_uniform(u_int32_t upper_bound)
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{
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u_int32_t r, min;
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if (upper_bound < 2)
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return 0;
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/* 2**32 % x == (2**32 - x) % x */
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min = -upper_bound % upper_bound;
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/*
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* This could theoretically loop forever but each retry has
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* p > 0.5 (worst case, usually far better) of selecting a
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* number inside the range we need, so it should rarely need
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* to re-roll.
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*/
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for (;;) {
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r = arc4random();
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if (r >= min)
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break;
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}
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return r % upper_bound;
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}
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#if 0
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/*-------- Test code for i386 --------*/
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#include <stdio.h>
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58
lib/libc/gen/arc4random_uniform.c
Normal file
58
lib/libc/gen/arc4random_uniform.c
Normal file
@ -0,0 +1,58 @@
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/* $OpenBSD: arc4random_uniform.c,v 1.2 2015/09/13 08:31:47 guenther Exp $ */
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/*
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* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* $FreeBSD$
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*/
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#include <sys/types.h>
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#include <stdlib.h>
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/*
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* Calculate a uniformly distributed random number less than upper_bound
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* avoiding "modulo bias".
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*
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* Uniformity is achieved by generating new random numbers until the one
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* returned is outside the range [0, 2**32 % upper_bound). This
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* guarantees the selected random number will be inside
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* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
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* after reduction modulo upper_bound.
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*/
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uint32_t
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arc4random_uniform(uint32_t upper_bound)
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{
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uint32_t r, min;
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if (upper_bound < 2)
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return 0;
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/* 2**32 % x == (2**32 - x) % x */
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min = -upper_bound % upper_bound;
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/*
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* This could theoretically loop forever but each retry has
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* p > 0.5 (worst case, usually far better) of selecting a
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* number inside the range we need, so it should rarely need
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* to re-roll.
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*/
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for (;;) {
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r = arc4random();
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if (r >= min)
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break;
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}
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return r % upper_bound;
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}
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