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| 1 /* | |
| 2 * lfsr.c | |
| 3 * | |
| 4 */ | |
| 5 | |
| 6 /* | |
| 7 * | |
| 8 * Copyright (c) 2001-2006, Cisco Systems, Inc. | |
| 9 * All rights reserved. | |
| 10 * | |
| 11 * Redistribution and use in source and binary forms, with or without | |
| 12 * modification, are permitted provided that the following conditions | |
| 13 * are met: | |
| 14 * | |
| 15 * Redistributions of source code must retain the above copyright | |
| 16 * notice, this list of conditions and the following disclaimer. | |
| 17 * | |
| 18 * Redistributions in binary form must reproduce the above | |
| 19 * copyright notice, this list of conditions and the following | |
| 20 * disclaimer in the documentation and/or other materials provided | |
| 21 * with the distribution. | |
| 22 * | |
| 23 * Neither the name of the Cisco Systems, Inc. nor the names of its | |
| 24 * contributors may be used to endorse or promote products derived | |
| 25 * from this software without specific prior written permission. | |
| 26 * | |
| 27 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
| 28 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
| 29 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS | |
| 30 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE | |
| 31 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, | |
| 32 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES | |
| 33 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR | |
| 34 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
| 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, | |
| 36 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) | |
| 37 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED | |
| 38 * OF THE POSSIBILITY OF SUCH DAMAGE. | |
| 39 * | |
| 40 */ | |
| 41 | |
| 42 #include <stdio.h> | |
| 43 #include "datatypes.h" | |
| 44 | |
| 45 uint32_t | |
| 46 parity(uint32_t x) { | |
| 47 | |
| 48 x ^= (x >> 16); | |
| 49 x ^= (x >> 8); | |
| 50 x ^= (x >> 4); | |
| 51 x ^= (x >> 2); | |
| 52 x ^= (x >> 1); | |
| 53 | |
| 54 return x & 1; | |
| 55 } | |
| 56 | |
| 57 | |
| 58 /* typedef struct { */ | |
| 59 /* uint32_t register[8]; */ | |
| 60 /* } lfsr_t; */ | |
| 61 | |
| 62 void | |
| 63 compute_period(uint32_t feedback_polynomial) { | |
| 64 int i; | |
| 65 v32_t lfsr; | |
| 66 v32_t mask; | |
| 67 | |
| 68 mask.value = feedback_polynomial; | |
| 69 lfsr.value = 1; | |
| 70 | |
| 71 printf("polynomial: %s\t", v32_bit_string(mask)); | |
| 72 | |
| 73 for (i=0; i < 256; i++) { | |
| 74 /* printf("%s\n", v32_bit_string(lfsr)); */ | |
| 75 if (parity(mask.value & lfsr.value)) | |
| 76 lfsr.value = ((lfsr.value << 1) | 1) & 0xff; | |
| 77 else | |
| 78 lfsr.value = (lfsr.value << 1) & 0xff; | |
| 79 | |
| 80 /* now halt if we're back at the initial state */ | |
| 81 if (lfsr.value == 1) { | |
| 82 printf("period: %d\n", i); | |
| 83 break; | |
| 84 } | |
| 85 } | |
| 86 } | |
| 87 | |
| 88 uint32_t poly0 = 223; | |
| 89 | |
| 90 | |
| 91 uint32_t polynomials[39] = { | |
| 92 31, | |
| 93 47, | |
| 94 55, | |
| 95 59, | |
| 96 61, | |
| 97 79, | |
| 98 87, | |
| 99 91, | |
| 100 103, | |
| 101 107, | |
| 102 109, | |
| 103 115, | |
| 104 117, | |
| 105 121, | |
| 106 143, | |
| 107 151, | |
| 108 157, | |
| 109 167, | |
| 110 171, | |
| 111 173, | |
| 112 179, | |
| 113 181, | |
| 114 185, | |
| 115 199, | |
| 116 203, | |
| 117 205, | |
| 118 211, | |
| 119 213, | |
| 120 227, | |
| 121 229, | |
| 122 233, | |
| 123 241, | |
| 124 127, | |
| 125 191, | |
| 126 223, | |
| 127 239, | |
| 128 247, | |
| 129 251, | |
| 130 253 | |
| 131 }; | |
| 132 | |
| 133 char binary_string[32]; | |
| 134 | |
| 135 char * | |
| 136 u32_bit_string(uint32_t x, unsigned int length) { | |
| 137 unsigned int mask; | |
| 138 int index; | |
| 139 | |
| 140 mask = 1 << length; | |
| 141 index = 0; | |
| 142 for (; mask > 0; mask >>= 1) | |
| 143 if ((x & mask) == 0) | |
| 144 binary_string[index++] = '0'; | |
| 145 else | |
| 146 binary_string[index++] = '1'; | |
| 147 | |
| 148 binary_string[index++] = 0; /* NULL terminate string */ | |
| 149 return binary_string; | |
| 150 } | |
| 151 | |
| 152 extern int octet_weight[256]; | |
| 153 | |
| 154 unsigned int | |
| 155 weight(uint32_t poly) { | |
| 156 int wt = 0; | |
| 157 | |
| 158 /* note: endian-ness makes no difference */ | |
| 159 wt += octet_weight[poly & 0xff]; | |
| 160 wt += octet_weight[(poly >> 8) & 0xff]; | |
| 161 wt += octet_weight[(poly >> 16) & 0xff]; | |
| 162 wt += octet_weight[(poly >> 24)]; | |
| 163 | |
| 164 return wt; | |
| 165 } | |
| 166 | |
| 167 #define MAX_PERIOD 65535 | |
| 168 | |
| 169 #define debug_print 0 | |
| 170 | |
| 171 int | |
| 172 period(uint32_t poly) { | |
| 173 int i; | |
| 174 uint32_t x; | |
| 175 | |
| 176 | |
| 177 /* set lfsr to 1 */ | |
| 178 x = 1; | |
| 179 #if debug_print | |
| 180 printf("%d:\t%s\n", 0, u32_bit_string(x,8)); | |
| 181 #endif | |
| 182 for (i=1; i < MAX_PERIOD; i++) { | |
| 183 if (x & 1) | |
| 184 x = (x >> 1) ^ poly; | |
| 185 else | |
| 186 x = (x >> 1); | |
| 187 | |
| 188 #if debug_print | |
| 189 /* print for a sanity check */ | |
| 190 printf("%d:\t%s\n", i, u32_bit_string(x,8)); | |
| 191 #endif | |
| 192 | |
| 193 /* check for return to original value */ | |
| 194 if (x == 1) | |
| 195 return i; | |
| 196 } | |
| 197 return i; | |
| 198 } | |
| 199 | |
| 200 /* | |
| 201 * weight distribution computes the weight distribution of the | |
| 202 * code generated by the polynomial poly | |
| 203 */ | |
| 204 | |
| 205 #define MAX_LEN 8 | |
| 206 #define MAX_WEIGHT (1 << MAX_LEN) | |
| 207 | |
| 208 int A[MAX_WEIGHT+1]; | |
| 209 | |
| 210 void | |
| 211 weight_distribution2(uint32_t poly, int *A) { | |
| 212 int i; | |
| 213 uint32_t x; | |
| 214 | |
| 215 /* zeroize array */ | |
| 216 for (i=0; i < MAX_WEIGHT+1; i++) | |
| 217 A[i] = 0; | |
| 218 | |
| 219 /* loop over all input sequences */ | |
| 220 | |
| 221 | |
| 222 /* set lfsr to 1 */ | |
| 223 x = 1; | |
| 224 #if debug_print | |
| 225 printf("%d:\t%s\n", 0, u32_bit_string(x,8)); | |
| 226 #endif | |
| 227 for (i=1; i < MAX_PERIOD; i++) { | |
| 228 if (x & 1) | |
| 229 x = (x >> 1) ^ poly; | |
| 230 else | |
| 231 x = (x >> 1); | |
| 232 | |
| 233 #if debug_print | |
| 234 /* print for a sanity check */ | |
| 235 printf("%d:\t%s\n", i, u32_bit_string(x,8)); | |
| 236 #endif | |
| 237 | |
| 238 /* increment weight */ | |
| 239 wt += (x & 1); | |
| 240 | |
| 241 /* check for return to original value */ | |
| 242 if (x == 1) | |
| 243 break; | |
| 244 } | |
| 245 | |
| 246 /* set zero */ | |
| 247 A[0] = 0; | |
| 248 } | |
| 249 | |
| 250 | |
| 251 void | |
| 252 weight_distribution(uint32_t poly, int *A) { | |
| 253 int i; | |
| 254 uint32_t x; | |
| 255 | |
| 256 /* zeroize array */ | |
| 257 for (i=0; i < MAX_WEIGHT+1; i++) | |
| 258 A[i] = 0; | |
| 259 | |
| 260 /* set lfsr to 1 */ | |
| 261 x = 1; | |
| 262 #if debug_print | |
| 263 printf("%d:\t%s\n", 0, u32_bit_string(x,8)); | |
| 264 #endif | |
| 265 for (i=1; i < MAX_PERIOD; i++) { | |
| 266 if (x & 1) | |
| 267 x = (x >> 1) ^ poly; | |
| 268 else | |
| 269 x = (x >> 1); | |
| 270 | |
| 271 #if debug_print | |
| 272 /* print for a sanity check */ | |
| 273 printf("%d:\t%s\n", i, u32_bit_string(x,8)); | |
| 274 #endif | |
| 275 | |
| 276 /* compute weight, increment proper element */ | |
| 277 A[weight(x)]++; | |
| 278 | |
| 279 /* check for return to original value */ | |
| 280 if (x == 1) | |
| 281 break; | |
| 282 } | |
| 283 | |
| 284 /* set zero */ | |
| 285 A[0] = 0; | |
| 286 } | |
| 287 | |
| 288 | |
| 289 | |
| 290 | |
| 291 int | |
| 292 main () { | |
| 293 | |
| 294 int i,j; | |
| 295 v32_t x; | |
| 296 v32_t p; | |
| 297 | |
| 298 /* originally 0xaf */ | |
| 299 p.value = 0x9; | |
| 300 | |
| 301 printf("polynomial: %s\tperiod: %d\n", | |
| 302 u32_bit_string(p.value,8), period(p.value)); | |
| 303 | |
| 304 /* compute weight distribution */ | |
| 305 weight_distribution(p.value, A); | |
| 306 | |
| 307 /* print weight distribution */ | |
| 308 for (i=0; i <= 8; i++) { | |
| 309 printf("A[%d]: %d\n", i, A[i]); | |
| 310 } | |
| 311 | |
| 312 #if 0 | |
| 313 for (i=0; i < 39; i++) { | |
| 314 printf("polynomial: %s\tperiod: %d\n", | |
| 315 u32_bit_string(polynomials[i],8), period(polynomials[i])); | |
| 316 | |
| 317 /* compute weight distribution */ | |
| 318 weight_distribution(p.value, A); | |
| 319 | |
| 320 /* print weight distribution */ | |
| 321 for (j=0; j <= 8; j++) { | |
| 322 printf("A[%d]: %d\n", j, A[j]); | |
| 323 } | |
| 324 } | |
| 325 #endif | |
| 326 | |
| 327 { | |
| 328 int bits = 8; | |
| 329 uint32_t y; | |
| 330 for (y=0; y < (1 << bits); y++) { | |
| 331 printf("polynomial: %s\tweight: %d\tperiod: %d\n", | |
| 332 u32_bit_string(y,bits), weight(y), period(y)); | |
| 333 | |
| 334 /* compute weight distribution */ | |
| 335 weight_distribution(y, A); | |
| 336 | |
| 337 /* print weight distribution */ | |
| 338 for (j=0; j <= 8; j++) { | |
| 339 printf("A[%d]: %d\n", j, A[j]); | |
| 340 } | |
| 341 } | |
| 342 } | |
| 343 | |
| 344 return 0; | |
| 345 } | |
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Chromium Code Reviews
Issue 2344973002:
Update libsrtp to version 2.0 (Closed)
