| 1 | /* $NetBSD: mertwist.c,v 1.8 2008/04/28 20:24:06 martin Exp $ */ |
| 2 | /*- |
| 3 | * Copyright (c) 2008 The NetBSD Foundation, Inc. |
| 4 | * All rights reserved. |
| 5 | * |
| 6 | * This code is derived from software contributed to The NetBSD Foundation |
| 7 | * by Matt Thomas <matt@3am-software.com>. |
| 8 | * |
| 9 | * Redistribution and use in source and binary forms, with or without |
| 10 | * modification, are permitted provided that the following conditions |
| 11 | * are met: |
| 12 | * 1. Redistributions of source code must retain the above copyright |
| 13 | * notice, this list of conditions and the following disclaimer. |
| 14 | * 2. Redistributions in binary form must reproduce the above copyright |
| 15 | * notice, this list of conditions and the following disclaimer in the |
| 16 | * documentation and/or other materials provided with the distribution. |
| 17 | * |
| 18 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
| 19 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
| 20 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| 21 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
| 22 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 23 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 24 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 25 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 26 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 27 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 28 | * POSSIBILITY OF SUCH DAMAGE. |
| 29 | */ |
| 30 | |
| 31 | #if defined(_KERNEL) || defined(_STANDALONE) |
| 32 | #include <sys/param.h> |
| 33 | #include <sys/types.h> |
| 34 | #include <sys/systm.h> |
| 35 | |
| 36 | #include <lib/libkern/libkern.h> |
| 37 | #else |
| 38 | #include <stdlib.h> |
| 39 | #include <string.h> |
| 40 | #include <inttypes.h> |
| 41 | #include <assert.h> |
| 42 | #define KASSERT(x) assert(x) |
| 43 | #endif |
| 44 | |
| 45 | /* |
| 46 | * Mersenne Twister. Produces identical output compared to mt19937ar.c |
| 47 | * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html |
| 48 | */ |
| 49 | |
| 50 | #define MATRIX_A(a) (((a) & 1) ? 0x9908b0df : 0) |
| 51 | #define TEMPERING_MASK_B 0x9d2c5680 |
| 52 | #define TEMPERING_MASK_C 0xefc60000 |
| 53 | #define UPPER_MASK 0x80000000 |
| 54 | #define LOWER_MASK 0x7fffffff |
| 55 | #define MIX(u,l) (((u) & UPPER_MASK) | ((l) & LOWER_MASK)) |
| 56 | |
| 57 | #define KNUTH_MULTIPLIER 0x6c078965 |
| 58 | |
| 59 | #ifndef MTPRNG_RLEN |
| 60 | #define MTPRNG_RLEN 624 |
| 61 | #endif |
| 62 | #define MTPRNG_POS1 397 |
| 63 | |
| 64 | static void mtprng_refresh(struct mtprng_state *); |
| 65 | |
| 66 | /* |
| 67 | * Initialize the generator from a seed |
| 68 | */ |
| 69 | void |
| 70 | mtprng_init32(struct mtprng_state *mt, uint32_t seed) |
| 71 | { |
| 72 | size_t i; |
| 73 | |
| 74 | /* |
| 75 | * Use Knuth's algorithm for expanding this seed over its |
| 76 | * portion of the key space. |
| 77 | */ |
| 78 | mt->mt_elem[0] = seed; |
| 79 | for (i = 1; i < MTPRNG_RLEN; i++) { |
| 80 | mt->mt_elem[i] = KNUTH_MULTIPLIER |
| 81 | * (mt->mt_elem[i-1] ^ (mt->mt_elem[i-1] >> 30)) + i; |
| 82 | } |
| 83 | |
| 84 | mtprng_refresh(mt); |
| 85 | } |
| 86 | |
| 87 | void |
| 88 | mtprng_initarray(struct mtprng_state *mt, const uint32_t *key, size_t keylen) |
| 89 | { |
| 90 | uint32_t *mp; |
| 91 | size_t i, j, k; |
| 92 | |
| 93 | /* |
| 94 | * Use Knuth's algorithm for expanding this seed over its |
| 95 | * portion of the key space. |
| 96 | */ |
| 97 | mt->mt_elem[0] = 19650218UL; |
| 98 | for (i = 1; i < MTPRNG_RLEN; i++) { |
| 99 | mt->mt_elem[i] = KNUTH_MULTIPLIER |
| 100 | * (mt->mt_elem[i-1] ^ (mt->mt_elem[i-1] >> 30)) + i; |
| 101 | } |
| 102 | |
| 103 | KASSERT(keylen > 0); |
| 104 | |
| 105 | i = 1; |
| 106 | j = 0; |
| 107 | k = (keylen < MTPRNG_RLEN ? MTPRNG_RLEN : keylen); |
| 108 | |
| 109 | mp = &mt->mt_elem[1]; |
| 110 | for (; k-- > 0; mp++) { |
| 111 | mp[0] ^= (mp[-1] ^ (mp[-1] >> 30)) * 1664525UL; |
| 112 | mp[0] += key[j] + j; |
| 113 | if (++i == MTPRNG_RLEN) { |
| 114 | KASSERT(mp == mt->mt_elem + MTPRNG_RLEN - 1); |
| 115 | mt->mt_elem[0] = mp[0]; |
| 116 | i = 1; |
| 117 | mp = mt->mt_elem; |
| 118 | } |
| 119 | if (++j == keylen) |
| 120 | j = 0; |
| 121 | } |
| 122 | for (j = MTPRNG_RLEN; --j > 0; mp++) { |
| 123 | mp[0] ^= (mp[-1] ^ (mp[-1] >> 30)) * 1566083941UL; |
| 124 | mp[0] -= i; |
| 125 | if (++i == MTPRNG_RLEN) { |
| 126 | KASSERT(mp == mt->mt_elem + MTPRNG_RLEN - 1); |
| 127 | mt->mt_elem[0] = mp[0]; |
| 128 | i = 1; |
| 129 | mp = mt->mt_elem; |
| 130 | } |
| 131 | } |
| 132 | mt->mt_elem[0] = 0x80000000; |
| 133 | mtprng_refresh(mt); |
| 134 | } |
| 135 | |
| 136 | /* |
| 137 | * Generate an array of 624 untempered numbers |
| 138 | */ |
| 139 | void |
| 140 | mtprng_refresh(struct mtprng_state *mt) |
| 141 | { |
| 142 | uint32_t y; |
| 143 | size_t i, j; |
| 144 | /* |
| 145 | * The following has been refactored to avoid the need for 'mod 624' |
| 146 | */ |
| 147 | for (i = 0, j = MTPRNG_POS1; j < MTPRNG_RLEN; i++, j++) { |
| 148 | y = MIX(mt->mt_elem[i], mt->mt_elem[i+1]); |
| 149 | mt->mt_elem[i] = mt->mt_elem[j] ^ (y >> 1) ^ MATRIX_A(y); |
| 150 | } |
| 151 | for (j = 0; i < MTPRNG_RLEN - 1; i++, j++) { |
| 152 | y = MIX(mt->mt_elem[i], mt->mt_elem[i+1]); |
| 153 | mt->mt_elem[i] = mt->mt_elem[j] ^ (y >> 1) ^ MATRIX_A(y); |
| 154 | } |
| 155 | y = MIX(mt->mt_elem[MTPRNG_RLEN - 1], mt->mt_elem[0]); |
| 156 | mt->mt_elem[MTPRNG_RLEN - 1] = |
| 157 | mt->mt_elem[MTPRNG_POS1 - 1] ^ (y >> 1) ^ MATRIX_A(y); |
| 158 | } |
| 159 | |
| 160 | /* |
| 161 | * Extract a tempered PRN based on the current index. Then recompute a |
| 162 | * new value for the index. This avoids having to regenerate the array |
| 163 | * every 624 iterations. We can do this since recomputing only the next |
| 164 | * element and the [(i + 397) % 624] one. |
| 165 | */ |
| 166 | uint32_t |
| 167 | mtprng_rawrandom(struct mtprng_state *mt) |
| 168 | { |
| 169 | uint32_t x, y; |
| 170 | const size_t i = mt->mt_idx; |
| 171 | size_t j; |
| 172 | |
| 173 | /* |
| 174 | * First generate the random value for the current position. |
| 175 | */ |
| 176 | x = mt->mt_elem[i]; |
| 177 | x ^= x >> 11; |
| 178 | x ^= (x << 7) & TEMPERING_MASK_B; |
| 179 | x ^= (x << 15) & TEMPERING_MASK_C; |
| 180 | x ^= x >> 18; |
| 181 | |
| 182 | /* |
| 183 | * Next recalculate the next sequence for the current position. |
| 184 | */ |
| 185 | y = mt->mt_elem[i]; |
| 186 | if (__predict_true(i < MTPRNG_RLEN - 1)) { |
| 187 | /* |
| 188 | * Avoid doing % since it can be expensive. |
| 189 | * j = (i + MTPRNG_POS1) % MTPRNG_RLEN; |
| 190 | */ |
| 191 | j = i + MTPRNG_POS1; |
| 192 | if (j >= MTPRNG_RLEN) |
| 193 | j -= MTPRNG_RLEN; |
| 194 | mt->mt_idx++; |
| 195 | } else { |
| 196 | j = MTPRNG_POS1 - 1; |
| 197 | mt->mt_idx = 0; |
| 198 | } |
| 199 | y = MIX(y, mt->mt_elem[mt->mt_idx]); |
| 200 | mt->mt_elem[i] = mt->mt_elem[j] ^ (y >> 1) ^ MATRIX_A(y); |
| 201 | |
| 202 | /* |
| 203 | * Return the value calculated in the first step. |
| 204 | */ |
| 205 | return x; |
| 206 | } |
| 207 | |
| 208 | /* |
| 209 | * This is a non-standard routine which attempts to return a cryptographically |
| 210 | * strong random number by collapsing 2 32bit values outputed by the twister |
| 211 | * into one 32bit value. |
| 212 | */ |
| 213 | uint32_t |
| 214 | mtprng_random(struct mtprng_state *mt) |
| 215 | { |
| 216 | uint32_t a; |
| 217 | |
| 218 | mt->mt_count = (mt->mt_count + 13) & 31; |
| 219 | a = mtprng_rawrandom(mt); |
| 220 | a = (a << mt->mt_count) | (a >> (32 - mt->mt_count)); |
| 221 | return a + mtprng_rawrandom(mt); |
| 222 | } |
| 223 | |