GCC Code Coverage Report
Directory: ./ Exec Total Coverage
File: lib/libc/net/res_random.c Lines: 0 54 0.0 %
Date: 2017-11-07 Branches: 0 34 0.0 %

Line Branch Exec Source
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/* $OpenBSD: res_random.c,v 1.24 2016/04/05 04:29:21 guenther Exp $ */
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/*
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 * Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
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 * Copyright 2008 Damien Miller <djm@openbsd.org>
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 * All rights reserved.
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 *
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 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
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 * such a mathematical system to generate more random (yet non-repeating)
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 * ids to solve the resolver/named problem.  But Niels designed the
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 * actual system based on the constraints.
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 *
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 * Later modified by Damien Miller to wrap the LCG output in a 15-bit
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 * permutation generator based on a Luby-Rackoff block cipher. This
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 * ensures the output is non-repeating and preserves the MSB twiddle
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 * trick, but makes it more resistant to LCG prediction.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *    documentation and/or other materials provided with the distribution.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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/*
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 * seed = random 15bit
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 * n = prime, g0 = generator to n,
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 * j = random so that gcd(j,n-1) == 1
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 * g = g0^j mod n will be a generator again.
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 *
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 * X[0] = random seed.
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 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
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 * with a = 7^(even random) mod m,
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 *      b = random with gcd(b,m) == 1
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 *      m = 31104 and a maximal period of m-1.
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 *
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 * The transaction id is determined by:
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 * id[n] = seed xor (g^X[n] mod n)
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 *
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 * Effectivly the id is restricted to the lower 15 bits, thus
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 * yielding two different cycles by toggling the msb on and off.
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 * This avoids reuse issues caused by reseeding.
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 *
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 * The output of this generator is then randomly permuted though a
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 * custom 15 bit Luby-Rackoff block cipher.
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 */
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#include <sys/types.h>
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#include <netinet/in.h>
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#include <sys/time.h>
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#include <resolv.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <string.h>
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#include "thread_private.h"
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#define RU_OUT  	180	/* Time after wich will be reseeded */
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#define RU_MAX		30000	/* Uniq cycle, avoid blackjack prediction */
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#define RU_GEN		2	/* Starting generator */
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#define RU_N		32749	/* RU_N-1 = 2*2*3*2729 */
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#define RU_AGEN		7	/* determine ru_a as RU_AGEN^(2*rand) */
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#define RU_M		31104	/* RU_M = 2^7*3^5 - don't change */
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#define RU_ROUNDS	11	/* Number of rounds for permute (odd) */
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struct prf_ctx {
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	/* PRF lookup table for odd rounds (7 bits input to 8 bits output) */
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	u_char prf7[(RU_ROUNDS / 2) * (1 << 7)];
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	/* PRF lookup table for even rounds (8 bits input to 7 bits output) */
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	u_char prf8[((RU_ROUNDS + 1) / 2) * (1 << 8)];
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};
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#define PFAC_N 3
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static const u_int16_t pfacts[PFAC_N] = {
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	2,
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	3,
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	2729
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};
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static u_int16_t ru_x;
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static u_int16_t ru_seed, ru_seed2;
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static u_int16_t ru_a, ru_b;
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static u_int16_t ru_g;
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static u_int16_t ru_counter = 0;
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static u_int16_t ru_msb = 0;
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static struct prf_ctx *ru_prf = NULL;
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static time_t ru_reseed;
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static pid_t ru_pid;
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static u_int16_t pmod(u_int16_t, u_int16_t, u_int16_t);
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static void res_initid(void);
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/*
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 * Do a fast modular exponation, returned value will be in the range
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 * of 0 - (mod-1)
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 */
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static u_int16_t
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pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod)
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{
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	u_int16_t s, t, u;
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	s = 1;
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	t = gen;
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	u = exp;
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	while (u) {
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		if (u & 1)
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			s = (s * t) % mod;
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		u >>= 1;
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		t = (t * t) % mod;
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	}
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	return (s);
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}
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/*
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 * 15-bit permutation based on Luby-Rackoff block cipher
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 */
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static u_int
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permute15(u_int in)
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{
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	int i;
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	u_int left, right, tmp;
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	if (ru_prf == NULL)
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		return in;
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	left = (in >> 8) & 0x7f;
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	right = in & 0xff;
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	/*
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	 * Each round swaps the width of left and right. Even rounds have
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	 * a 7-bit left, odd rounds have an 8-bit left.	Since this uses an
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	 * odd number of rounds, left is always 8 bits wide at the end.
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	 */
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	for (i = 0; i < RU_ROUNDS; i++) {
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		if ((i & 1) == 0)
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			tmp = ru_prf->prf8[(i << (8 - 1)) | right] & 0x7f;
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		else
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			tmp = ru_prf->prf7[((i - 1) << (7 - 1)) | right];
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		tmp ^= left;
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		left = right;
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		right = tmp;
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	}
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	return (right << 8) | left;
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}
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/*
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 * Initializes the seed and chooses a suitable generator. Also toggles
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 * the msb flag. The msb flag is used to generate two distinct
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 * cycles of random numbers and thus avoiding reuse of ids.
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 *
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 * This function is called from res_randomid() when needed, an
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 * application does not have to worry about it.
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 */
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static void
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res_initid(void)
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{
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	u_int16_t j, i;
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	u_int32_t tmp;
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	int noprime = 1;
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	struct timespec ts;
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	ru_x = arc4random_uniform(RU_M);
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	/* 15 bits of random seed */
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	tmp = arc4random();
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	ru_seed = (tmp >> 16) & 0x7FFF;
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	ru_seed2 = tmp & 0x7FFF;
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	/* Determine the LCG we use */
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	tmp = arc4random();
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	ru_b = (tmp & 0xfffe) | 1;
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	ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
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	while (ru_b % 3 == 0)
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		ru_b += 2;
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	j = arc4random_uniform(RU_N);
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	/*
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	 * Do a fast gcd(j,RU_N-1), so we can find a j with
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	 * gcd(j, RU_N-1) == 1, giving a new generator for
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	 * RU_GEN^j mod RU_N
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	 */
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	while (noprime) {
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		for (i = 0; i < PFAC_N; i++)
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			if (j % pfacts[i] == 0)
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				break;
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		if (i >= PFAC_N)
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			noprime = 0;
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		else
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			j = (j + 1) % RU_N;
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	}
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	ru_g = pmod(RU_GEN, j, RU_N);
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	ru_counter = 0;
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	/* Initialise PRF for Luby-Rackoff permutation */
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	if (ru_prf == NULL)
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		ru_prf = malloc(sizeof(*ru_prf));
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	if (ru_prf != NULL)
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		arc4random_buf(ru_prf, sizeof(*ru_prf));
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	clock_gettime(CLOCK_MONOTONIC, &ts);
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	ru_reseed = ts.tv_sec + RU_OUT;
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	ru_msb = ru_msb == 0x8000 ? 0 : 0x8000;
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}
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u_int
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__res_randomid(void)
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{
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	struct timespec ts;
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	pid_t pid;
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	u_int r;
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	static void *randomid_mutex;
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	clock_gettime(CLOCK_MONOTONIC, &ts);
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	pid = getpid();
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	_MUTEX_LOCK(&randomid_mutex);
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	if (ru_counter >= RU_MAX || ts.tv_sec > ru_reseed || pid != ru_pid) {
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		res_initid();
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		ru_pid = pid;
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	}
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	/* Linear Congruential Generator */
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	ru_x = (ru_a * ru_x + ru_b) % RU_M;
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	ru_counter++;
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	r = permute15(ru_seed ^ pmod(ru_g, ru_seed2 + ru_x, RU_N)) | ru_msb;
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	_MUTEX_UNLOCK(&randomid_mutex);
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	return (r);
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}
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DEF_STRONG(__res_randomid);
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#if 0
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int
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main(int argc, char **argv)
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{
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	int i, n;
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	u_int16_t wert;
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	res_initid();
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	printf("Generator: %u\n", ru_g);
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	printf("Seed: %u\n", ru_seed);
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	printf("Reseed at %ld\n", ru_reseed);
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	printf("Ru_X: %u\n", ru_x);
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	printf("Ru_A: %u\n", ru_a);
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	printf("Ru_B: %u\n", ru_b);
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	n = argc > 1 ? atoi(argv[1]) : 60001;
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	for (i=0;i<n;i++) {
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		wert = res_randomid();
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		printf("%u\n", wert);
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	}
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	return 0;
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}
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#endif
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