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/*
* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
*
* SPDX-License-Identifier: MPL-2.0
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, you can obtain one at https://mozilla.org/MPL/2.0/.
*
* See the COPYRIGHT file distributed with this work for additional
* information regarding copyright ownership.
*/
/*
* Portions of isc_random_uniform():
*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* 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 <inttypes.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <isc/once.h>
#include <isc/platform.h>
#include <isc/random.h>
#include <isc/result.h>
#include <isc/thread.h>
#include <isc/types.h>
#include <isc/util.h>
#include "entropy_private.h"
/*
* The specific implementation for PRNG is included as a C file
* that has to provide a static variable named seed, and a function
* uint32_t next(void) that provides next random number.
*
* The implementation must be thread-safe.
*/
/*
* Two contestants have been considered: the xoroshiro family of the
* functions by Villa&Blackman, and PCG by O'Neill. After
* consideration, the xoshiro128starstar function has been chosen as
* the uint32_t random number provider because it is very fast and has
* good enough properties for our usage pattern.
*/
#include "xoshiro128starstar.c"
ISC_THREAD_LOCAL isc_once_t isc_random_once = ISC_ONCE_INIT;
static void
isc_random_initialize(void) {
int useed[4] = { 0, 0, 0, 1 };
#if FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
/*
* Set a constant seed to help in problem reproduction should fuzzing
* find a crash or a hang. The seed array must be non-zero else
* xoshiro128starstar will generate an infinite series of zeroes.
*/
#else /* if FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
isc_entropy_get(useed, sizeof(useed));
#endif /* if FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
memmove(seed, useed, sizeof(seed));
}
uint8_t
isc_random8(void) {
RUNTIME_CHECK(isc_once_do(&isc_random_once, isc_random_initialize) ==
ISC_R_SUCCESS);
return (next() & 0xff);
}
uint16_t
isc_random16(void) {
RUNTIME_CHECK(isc_once_do(&isc_random_once, isc_random_initialize) ==
ISC_R_SUCCESS);
return (next() & 0xffff);
}
uint32_t
isc_random32(void) {
RUNTIME_CHECK(isc_once_do(&isc_random_once, isc_random_initialize) ==
ISC_R_SUCCESS);
return (next());
}
void
isc_random_buf(void *buf, size_t buflen) {
int i;
uint32_t r;
REQUIRE(buf != NULL);
REQUIRE(buflen > 0);
RUNTIME_CHECK(isc_once_do(&isc_random_once, isc_random_initialize) ==
ISC_R_SUCCESS);
for (i = 0; i + sizeof(r) <= buflen; i += sizeof(r)) {
r = next();
memmove((uint8_t *)buf + i, &r, sizeof(r));
}
r = next();
memmove((uint8_t *)buf + i, &r, buflen % sizeof(r));
return;
}
uint32_t
isc_random_uniform(uint32_t upper_bound) {
/* Copy of arc4random_uniform from OpenBSD */
uint32_t r, min;
RUNTIME_CHECK(isc_once_do(&isc_random_once, isc_random_initialize) ==
ISC_R_SUCCESS);
if (upper_bound < 2) {
return (0);
}
#if (ULONG_MAX > 0xffffffffUL)
min = 0x100000000UL % upper_bound;
#else /* if (ULONG_MAX > 0xffffffffUL) */
/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
if (upper_bound > 0x80000000) {
min = 1 + ~upper_bound; /* 2**32 - upper_bound */
} else {
/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
}
#endif /* if (ULONG_MAX > 0xffffffffUL) */
/*
* 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 = next();
if (r >= min) {
break;
}
}
return (r % upper_bound);
}
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