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annotate packages/net/tcpip/current/src/sys/netinet/ip_id.c @ 97:ced4577552cd ecos-sw-2000-06-06

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Merge from eCos master repository on 2000-06-06-08:44:00-BST
author jlarmour
date Tue, 06 Jun 2000 08:39:36 +0000
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1 //==========================================================================
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2 //
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3 // sys/netinet/ip_id.c
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4 //
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5 //
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6 //
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7 //==========================================================================
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8 //####COPYRIGHTBEGIN####
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9 //
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10 // -------------------------------------------
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11 // The contents of this file are subject to the Red Hat eCos Public License
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12 // Version 1.1 (the "License"); you may not use this file except in
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13 // compliance with the License. You may obtain a copy of the License at
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14 // http://www.redhat.com/
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15 //
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16 // Software distributed under the License is distributed on an "AS IS"
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17 // basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
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18 // License for the specific language governing rights and limitations under
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19 // the License.
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20 //
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21 // The Original Code is eCos - Embedded Configurable Operating System,
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22 // released September 30, 1998.
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23 //
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24 // The Initial Developer of the Original Code is Red Hat.
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25 // Portions created by Red Hat are
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26 // Copyright (C) 1998, 1999, 2000 Red Hat, Inc.
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27 // All Rights Reserved.
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28 // -------------------------------------------
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29 //
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30 //####COPYRIGHTEND####
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31 //####BSDCOPYRIGHTBEGIN####
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32 //
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33 // -------------------------------------------
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34 //
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35 // Portions of this software may have been derived from OpenBSD or other sources,
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36 // and are covered by the appropriate copyright disclaimers included herein.
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37 //
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38 // -------------------------------------------
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39 //
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40 //####BSDCOPYRIGHTEND####
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41 //==========================================================================
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42 //#####DESCRIPTIONBEGIN####
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43 //
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44 // Author(s): gthomas
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45 // Contributors: gthomas
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46 // Date: 2000-01-10
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47 // Purpose:
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48 // Description:
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49 //
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50 //
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51 //####DESCRIPTIONEND####
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52 //
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53 //==========================================================================
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54
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55
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56 /* $OpenBSD: ip_id.c,v 1.2 1999/08/26 13:37:01 provos Exp $ */
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57
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58 /*
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59 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
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60 * All rights reserved.
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61 *
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62 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
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63 * such a mathematical system to generate more random (yet non-repeating)
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64 * ids to solve the resolver/named problem. But Niels designed the
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65 * actual system based on the constraints.
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66 *
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67 * Redistribution and use in source and binary forms, with or without
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68 * modification, are permitted provided that the following conditions
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69 * are met:
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70 * 1. Redistributions of source code must retain the above copyright
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71 * notice, this list of conditions and the following disclaimer.
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72 * 2. Redistributions in binary form must reproduce the above copyright
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73 * notice, this list of conditions and the following disclaimer in the
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74 * documentation and/or other materials provided with the distribution.
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75 * 3. All advertising materials mentioning features or use of this software
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76 * must display the following acknowledgement:
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77 * This product includes software developed by Niels Provos.
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78 * 4. The name of the author may not be used to endorse or promote products
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79 * derived from this software without specific prior written permission.
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80 *
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81 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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82 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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83 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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84 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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85 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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86 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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87 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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88 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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89 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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90 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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91 */
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92
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93 /*
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94 * seed = random 15bit
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95 * n = prime, g0 = generator to n,
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96 * j = random so that gcd(j,n-1) == 1
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97 * g = g0^j mod n will be a generator again.
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98 *
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99 * X[0] = random seed.
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100 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
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101 * with a = 7^(even random) mod m,
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102 * b = random with gcd(b,m) == 1
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103 * m = 31104 and a maximal period of m-1.
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104 *
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105 * The transaction id is determined by:
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106 * id[n] = seed xor (g^X[n] mod n)
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107 *
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108 * Effectivly the id is restricted to the lower 15 bits, thus
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109 * yielding two different cycles by toggling the msb on and off.
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110 * This avoids reuse issues caused by reseeding.
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111 */
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112
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113 #include <sys/param.h>
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114 #include <sys/time.h>
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115 #include <sys/kernel.h>
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116
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117 #ifndef __ECOS
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118 #include <dev/rndvar.h>
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119 #endif
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120
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121 #define RU_OUT 180 /* Time after wich will be reseeded */
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122 #define RU_MAX 30000 /* Uniq cycle, avoid blackjack prediction */
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123 #define RU_GEN 2 /* Starting generator */
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124 #define RU_N 32749 /* RU_N-1 = 2*2*3*2729 */
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125 #define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2*rand) */
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126 #define RU_M 31104 /* RU_M = 2^7*3^5 - don't change */
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127
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128 #define PFAC_N 3
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129 const static u_int16_t pfacts[PFAC_N] = {
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130 2,
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131 3,
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132 2729
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133 };
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134
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135 static u_int16_t ru_x;
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136 static u_int16_t ru_seed, ru_seed2;
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137 static u_int16_t ru_a, ru_b;
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138 static u_int16_t ru_g;
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139 static u_int16_t ru_counter = 0;
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140 static u_int16_t ru_msb = 0;
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141 static long ru_reseed;
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142 static u_int32_t tmp; /* Storage for unused random */
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143
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144 static u_int16_t pmod __P((u_int16_t, u_int16_t, u_int16_t));
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145 static void ip_initid __P((void));
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146 u_int16_t ip_randomid __P((void));
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147
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148 /*
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149 * Do a fast modular exponation, returned value will be in the range
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150 * of 0 - (mod-1)
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151 */
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152
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153 #ifdef __STDC__
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154 static u_int16_t
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155 pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod)
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156 #else
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157 static u_int16_t
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158 pmod(gen, exp, mod)
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159 u_int16_t gen, exp, mod;
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160 #endif
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161 {
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162 u_int16_t s, t, u;
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163
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164 s = 1;
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165 t = gen;
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166 u = exp;
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167
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168 while (u) {
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169 if (u & 1)
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170 s = (s*t) % mod;
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171 u >>= 1;
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172 t = (t*t) % mod;
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173 }
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174 return (s);
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175 }
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176
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177 /*
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178 * Initalizes the seed and chooses a suitable generator. Also toggles
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179 * the msb flag. The msb flag is used to generate two distinct
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180 * cycles of random numbers and thus avoiding reuse of ids.
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181 *
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182 * This function is called from id_randomid() when needed, an
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183 * application does not have to worry about it.
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184 */
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185 static void
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186 ip_initid(void)
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187 {
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188 u_int16_t j, i;
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189 int noprime = 1;
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190
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191 get_random_bytes((void *) &tmp, sizeof(tmp));
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192 ru_x = (tmp & 0xFFFF) % RU_M;
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193
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194 /* 15 bits of random seed */
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195 ru_seed = (tmp >> 16) & 0x7FFF;
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196 get_random_bytes((void *) &tmp, sizeof(tmp));
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197 ru_seed2 = tmp & 0x7FFF;
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198
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199 get_random_bytes((void *) &tmp, sizeof(tmp));
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200
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201 /* Determine the LCG we use */
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202 ru_b = (tmp & 0xfffe) | 1;
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203 ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
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204 while (ru_b % 3 == 0)
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205 ru_b += 2;
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206
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207 get_random_bytes((void *) &tmp, sizeof(tmp));
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208 j = tmp % RU_N;
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209 tmp = tmp >> 16;
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210
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211 /*
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212 * Do a fast gcd(j,RU_N-1), so we can find a j with
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213 * gcd(j, RU_N-1) == 1, giving a new generator for
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214 * RU_GEN^j mod RU_N
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215 */
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216
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217 while (noprime) {
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218 for (i=0; i<PFAC_N; i++)
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219 if (j%pfacts[i] == 0)
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220 break;
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221
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222 if (i>=PFAC_N)
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223 noprime = 0;
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224 else
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225 j = (j+1) % RU_N;
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226 }
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227
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228 ru_g = pmod(RU_GEN,j,RU_N);
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229 ru_counter = 0;
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230
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231 ru_reseed = time.tv_sec + RU_OUT;
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232 ru_msb = ru_msb == 0x8000 ? 0 : 0x8000;
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233 }
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234
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235 u_int16_t
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236 ip_randomid(void)
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237 {
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238 int i, n;
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239
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240 if (ru_counter >= RU_MAX || time.tv_sec > ru_reseed)
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241 ip_initid();
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242
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243 if (!tmp)
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244 get_random_bytes((void *) &tmp, sizeof(tmp));
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245
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246 /* Skip a random number of ids */
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247 n = tmp & 0x3; tmp = tmp >> 2;
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248 if (ru_counter + n >= RU_MAX)
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249 ip_initid();
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250
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251 for (i = 0; i <= n; i++)
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252 /* Linear Congruential Generator */
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253 ru_x = (ru_a*ru_x + ru_b) % RU_M;
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254
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255 ru_counter += i;
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256
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257 return (ru_seed ^ pmod(ru_g,ru_seed2 ^ ru_x,RU_N)) | ru_msb;
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258 }