Neels Hofmeyr | 17518fe | 2017-06-20 04:35:06 +0200 | [diff] [blame] | 1 | /*! \file conv.c |
| 2 | * Generic convolutional encoding / decoding. */ |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 3 | /* |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 4 | * Copyright (C) 2011 Sylvain Munaut <tnt@246tNt.com> |
| 5 | * |
| 6 | * All Rights Reserved |
| 7 | * |
Harald Welte | e08da97 | 2017-11-13 01:00:26 +0900 | [diff] [blame] | 8 | * SPDX-License-Identifier: GPL-2.0+ |
| 9 | * |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 10 | * This program is free software; you can redistribute it and/or modify |
| 11 | * it under the terms of the GNU General Public License as published by |
| 12 | * the Free Software Foundation; either version 2 of the License, or |
| 13 | * (at your option) any later version. |
| 14 | * |
| 15 | * This program is distributed in the hope that it will be useful, |
| 16 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 17 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 18 | * GNU General Public License for more details. |
| 19 | * |
| 20 | * You should have received a copy of the GNU General Public License along |
| 21 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 22 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| 23 | */ |
| 24 | |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 25 | /*! \addtogroup conv |
| 26 | * @{ |
Neels Hofmeyr | 17518fe | 2017-06-20 04:35:06 +0200 | [diff] [blame] | 27 | * Osmocom convolutional encoder and decoder. |
| 28 | * |
| 29 | * \file conv.c */ |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 30 | |
Holger Hans Peter Freyther | 4772348 | 2011-11-09 11:26:15 +0100 | [diff] [blame] | 31 | #include "config.h" |
| 32 | #ifdef HAVE_ALLOCA_H |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 33 | #include <alloca.h> |
Holger Hans Peter Freyther | 4772348 | 2011-11-09 11:26:15 +0100 | [diff] [blame] | 34 | #endif |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 35 | #include <stdint.h> |
| 36 | #include <stdlib.h> |
| 37 | #include <string.h> |
| 38 | |
Vadim Yanitskiy | a8809f0 | 2020-02-09 04:12:53 +0700 | [diff] [blame] | 39 | #include <osmocom/core/utils.h> |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 40 | #include <osmocom/core/bits.h> |
| 41 | #include <osmocom/core/conv.h> |
| 42 | |
| 43 | |
| 44 | /* ------------------------------------------------------------------------ */ |
Sylvain Munaut | ae8dbb4 | 2011-11-24 17:47:32 +0100 | [diff] [blame] | 45 | /* Common */ |
| 46 | /* ------------------------------------------------------------------------ */ |
| 47 | |
| 48 | int |
| 49 | osmo_conv_get_input_length(const struct osmo_conv_code *code, int len) |
| 50 | { |
| 51 | return len <= 0 ? code->len : len; |
| 52 | } |
| 53 | |
| 54 | int |
| 55 | osmo_conv_get_output_length(const struct osmo_conv_code *code, int len) |
| 56 | { |
| 57 | int pbits, in_len, out_len; |
| 58 | |
| 59 | /* Input length */ |
| 60 | in_len = osmo_conv_get_input_length(code, len); |
| 61 | |
| 62 | /* Output length */ |
| 63 | out_len = in_len * code->N; |
| 64 | |
| 65 | if (code->term == CONV_TERM_FLUSH) |
| 66 | out_len += code->N * (code->K - 1); |
| 67 | |
| 68 | /* Count punctured bits */ |
| 69 | if (code->puncture) { |
| 70 | for (pbits=0; code->puncture[pbits] >= 0; pbits++); |
| 71 | out_len -= pbits; |
| 72 | } |
| 73 | |
| 74 | return out_len; |
| 75 | } |
| 76 | |
| 77 | |
| 78 | /* ------------------------------------------------------------------------ */ |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 79 | /* Encoding */ |
| 80 | /* ------------------------------------------------------------------------ */ |
| 81 | |
Neels Hofmeyr | 87e4550 | 2017-06-20 00:17:59 +0200 | [diff] [blame] | 82 | /*! Initialize a convolutional encoder |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 83 | * \param[in,out] encoder Encoder state to initialize |
| 84 | * \param[in] code Description of convolutional code |
| 85 | */ |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 86 | void |
| 87 | osmo_conv_encode_init(struct osmo_conv_encoder *encoder, |
| 88 | const struct osmo_conv_code *code) |
| 89 | { |
| 90 | memset(encoder, 0x00, sizeof(struct osmo_conv_encoder)); |
Vadim Yanitskiy | a8809f0 | 2020-02-09 04:12:53 +0700 | [diff] [blame] | 91 | OSMO_ASSERT(code != NULL); |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 92 | encoder->code = code; |
| 93 | } |
| 94 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 95 | void |
| 96 | osmo_conv_encode_load_state(struct osmo_conv_encoder *encoder, |
| 97 | const ubit_t *input) |
| 98 | { |
| 99 | int i; |
| 100 | uint8_t state = 0; |
| 101 | |
| 102 | for (i=0; i<(encoder->code->K-1); i++) |
| 103 | state = (state << 1) | input[i]; |
| 104 | |
| 105 | encoder->state = state; |
| 106 | } |
| 107 | |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 108 | static inline int |
| 109 | _conv_encode_do_output(struct osmo_conv_encoder *encoder, |
| 110 | uint8_t out, ubit_t *output) |
| 111 | { |
| 112 | const struct osmo_conv_code *code = encoder->code; |
| 113 | int o_idx = 0; |
| 114 | int j; |
| 115 | |
| 116 | if (code->puncture) { |
| 117 | for (j=0; j<code->N; j++) |
| 118 | { |
| 119 | int bit_no = code->N - j - 1; |
| 120 | int r_idx = encoder->i_idx * code->N + j; |
| 121 | |
| 122 | if (code->puncture[encoder->p_idx] == r_idx) |
| 123 | encoder->p_idx++; |
| 124 | else |
| 125 | output[o_idx++] = (out >> bit_no) & 1; |
| 126 | } |
| 127 | } else { |
| 128 | for (j=0; j<code->N; j++) |
| 129 | { |
| 130 | int bit_no = code->N - j - 1; |
| 131 | output[o_idx++] = (out >> bit_no) & 1; |
| 132 | } |
| 133 | } |
| 134 | |
| 135 | return o_idx; |
| 136 | } |
| 137 | |
| 138 | int |
| 139 | osmo_conv_encode_raw(struct osmo_conv_encoder *encoder, |
| 140 | const ubit_t *input, ubit_t *output, int n) |
| 141 | { |
| 142 | const struct osmo_conv_code *code = encoder->code; |
| 143 | uint8_t state; |
| 144 | int i; |
| 145 | int o_idx; |
| 146 | |
| 147 | o_idx = 0; |
| 148 | state = encoder->state; |
| 149 | |
| 150 | for (i=0; i<n; i++) { |
| 151 | int bit = input[i]; |
| 152 | uint8_t out; |
| 153 | |
| 154 | out = code->next_output[state][bit]; |
| 155 | state = code->next_state[state][bit]; |
| 156 | |
| 157 | o_idx += _conv_encode_do_output(encoder, out, &output[o_idx]); |
| 158 | |
| 159 | encoder->i_idx++; |
| 160 | } |
| 161 | |
| 162 | encoder->state = state; |
| 163 | |
| 164 | return o_idx; |
| 165 | } |
| 166 | |
| 167 | int |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 168 | osmo_conv_encode_flush(struct osmo_conv_encoder *encoder, |
| 169 | ubit_t *output) |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 170 | { |
| 171 | const struct osmo_conv_code *code = encoder->code; |
| 172 | uint8_t state; |
| 173 | int n; |
| 174 | int i; |
| 175 | int o_idx; |
| 176 | |
| 177 | n = code->K - 1; |
| 178 | |
| 179 | o_idx = 0; |
| 180 | state = encoder->state; |
| 181 | |
| 182 | for (i=0; i<n; i++) { |
| 183 | uint8_t out; |
| 184 | |
| 185 | if (code->next_term_output) { |
| 186 | out = code->next_term_output[state]; |
| 187 | state = code->next_term_state[state]; |
| 188 | } else { |
| 189 | out = code->next_output[state][0]; |
| 190 | state = code->next_state[state][0]; |
| 191 | } |
| 192 | |
| 193 | o_idx += _conv_encode_do_output(encoder, out, &output[o_idx]); |
| 194 | |
| 195 | encoder->i_idx++; |
| 196 | } |
| 197 | |
| 198 | encoder->state = state; |
| 199 | |
| 200 | return o_idx; |
| 201 | } |
| 202 | |
Neels Hofmeyr | 87e4550 | 2017-06-20 00:17:59 +0200 | [diff] [blame] | 203 | /*! All-in-one convolutional encoding function |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 204 | * \param[in] code description of convolutional code to be used |
| 205 | * \param[in] input array of unpacked bits (uncoded) |
| 206 | * \param[out] output array of unpacked bits (encoded) |
Sylvain Munaut | 03d2c89 | 2011-11-24 11:53:49 +0100 | [diff] [blame] | 207 | * \return Number of produced output bits |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 208 | * |
| 209 | * This is an all-in-one function, taking care of |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 210 | * \ref osmo_conv_init, \ref osmo_conv_encode_load_state, |
| 211 | * \ref osmo_conv_encode_raw and \ref osmo_conv_encode_flush as needed. |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 212 | */ |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 213 | int |
| 214 | osmo_conv_encode(const struct osmo_conv_code *code, |
| 215 | const ubit_t *input, ubit_t *output) |
| 216 | { |
| 217 | struct osmo_conv_encoder encoder; |
| 218 | int l; |
| 219 | |
| 220 | osmo_conv_encode_init(&encoder, code); |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 221 | |
| 222 | if (code->term == CONV_TERM_TAIL_BITING) { |
| 223 | int eidx = code->len - code->K + 1; |
| 224 | osmo_conv_encode_load_state(&encoder, &input[eidx]); |
| 225 | } |
| 226 | |
| 227 | l = osmo_conv_encode_raw(&encoder, input, output, code->len); |
| 228 | |
| 229 | if (code->term == CONV_TERM_FLUSH) |
| 230 | l += osmo_conv_encode_flush(&encoder, &output[l]); |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 231 | |
| 232 | return l; |
| 233 | } |
| 234 | |
| 235 | |
| 236 | /* ------------------------------------------------------------------------ */ |
| 237 | /* Decoding (viterbi) */ |
| 238 | /* ------------------------------------------------------------------------ */ |
| 239 | |
| 240 | #define MAX_AE 0x00ffffff |
| 241 | |
Tom Tsou | 3553680 | 2016-11-24 19:24:32 +0700 | [diff] [blame] | 242 | /* Forward declaration for accerlated decoding with certain codes */ |
| 243 | int |
| 244 | osmo_conv_decode_acc(const struct osmo_conv_code *code, |
| 245 | const sbit_t *input, ubit_t *output); |
| 246 | |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 247 | void |
| 248 | osmo_conv_decode_init(struct osmo_conv_decoder *decoder, |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 249 | const struct osmo_conv_code *code, int len, int start_state) |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 250 | { |
| 251 | int n_states; |
| 252 | |
| 253 | /* Init */ |
| 254 | if (len <= 0) |
| 255 | len = code->len; |
| 256 | |
| 257 | n_states = 1 << (code->K - 1); |
| 258 | |
| 259 | memset(decoder, 0x00, sizeof(struct osmo_conv_decoder)); |
| 260 | |
| 261 | decoder->code = code; |
| 262 | decoder->n_states = n_states; |
| 263 | decoder->len = len; |
| 264 | |
| 265 | /* Allocate arrays */ |
| 266 | decoder->ae = malloc(sizeof(unsigned int) * n_states); |
| 267 | decoder->ae_next = malloc(sizeof(unsigned int) * n_states); |
| 268 | |
| 269 | decoder->state_history = malloc(sizeof(uint8_t) * n_states * (len + decoder->code->K - 1)); |
| 270 | |
| 271 | /* Classic reset */ |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 272 | osmo_conv_decode_reset(decoder, start_state); |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 273 | } |
| 274 | |
| 275 | void |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 276 | osmo_conv_decode_reset(struct osmo_conv_decoder *decoder, int start_state) |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 277 | { |
| 278 | int i; |
| 279 | |
| 280 | /* Reset indexes */ |
| 281 | decoder->o_idx = 0; |
| 282 | decoder->p_idx = 0; |
| 283 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 284 | /* Initial error */ |
| 285 | if (start_state < 0) { |
| 286 | /* All states possible */ |
| 287 | memset(decoder->ae, 0x00, sizeof(unsigned int) * decoder->n_states); |
| 288 | } else { |
| 289 | /* Fixed start state */ |
| 290 | for (i=0; i<decoder->n_states; i++) { |
| 291 | decoder->ae[i] = (i == start_state) ? 0 : MAX_AE; |
| 292 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 293 | } |
| 294 | } |
| 295 | |
| 296 | void |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 297 | osmo_conv_decode_rewind(struct osmo_conv_decoder *decoder) |
| 298 | { |
| 299 | int i; |
| 300 | unsigned int min_ae = MAX_AE; |
| 301 | |
| 302 | /* Reset indexes */ |
| 303 | decoder->o_idx = 0; |
| 304 | decoder->p_idx = 0; |
| 305 | |
| 306 | /* Initial error normalize (remove constant) */ |
| 307 | for (i=0; i<decoder->n_states; i++) { |
| 308 | if (decoder->ae[i] < min_ae) |
| 309 | min_ae = decoder->ae[i]; |
| 310 | } |
| 311 | |
| 312 | for (i=0; i<decoder->n_states; i++) |
| 313 | decoder->ae[i] -= min_ae; |
| 314 | } |
| 315 | |
| 316 | void |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 317 | osmo_conv_decode_deinit(struct osmo_conv_decoder *decoder) |
| 318 | { |
| 319 | free(decoder->ae); |
| 320 | free(decoder->ae_next); |
| 321 | free(decoder->state_history); |
| 322 | |
| 323 | memset(decoder, 0x00, sizeof(struct osmo_conv_decoder)); |
| 324 | } |
| 325 | |
| 326 | int |
| 327 | osmo_conv_decode_scan(struct osmo_conv_decoder *decoder, |
| 328 | const sbit_t *input, int n) |
| 329 | { |
| 330 | const struct osmo_conv_code *code = decoder->code; |
| 331 | |
| 332 | int i, s, b, j; |
| 333 | |
| 334 | int n_states; |
| 335 | unsigned int *ae; |
| 336 | unsigned int *ae_next; |
| 337 | uint8_t *state_history; |
| 338 | sbit_t *in_sym; |
| 339 | |
| 340 | int i_idx, p_idx; |
| 341 | |
| 342 | /* Prepare */ |
| 343 | n_states = decoder->n_states; |
| 344 | |
| 345 | ae = decoder->ae; |
| 346 | ae_next = decoder->ae_next; |
| 347 | state_history = &decoder->state_history[n_states * decoder->o_idx]; |
| 348 | |
| 349 | in_sym = alloca(sizeof(sbit_t) * code->N); |
| 350 | |
| 351 | i_idx = 0; |
| 352 | p_idx = decoder->p_idx; |
| 353 | |
| 354 | /* Scan the treillis */ |
| 355 | for (i=0; i<n; i++) |
| 356 | { |
| 357 | /* Reset next accumulated error */ |
| 358 | for (s=0; s<n_states; s++) { |
| 359 | ae_next[s] = MAX_AE; |
| 360 | } |
| 361 | |
| 362 | /* Get input */ |
| 363 | if (code->puncture) { |
| 364 | /* Hard way ... */ |
| 365 | for (j=0; j<code->N; j++) { |
| 366 | int idx = ((decoder->o_idx + i) * code->N) + j; |
| 367 | if (idx == code->puncture[p_idx]) { |
| 368 | in_sym[j] = 0; /* Undefined */ |
| 369 | p_idx++; |
| 370 | } else { |
| 371 | in_sym[j] = input[i_idx]; |
| 372 | i_idx++; |
| 373 | } |
| 374 | } |
| 375 | } else { |
| 376 | /* Easy, just copy N bits */ |
| 377 | memcpy(in_sym, &input[i_idx], code->N); |
| 378 | i_idx += code->N; |
| 379 | } |
| 380 | |
| 381 | /* Scan all state */ |
| 382 | for (s=0; s<n_states; s++) |
| 383 | { |
| 384 | /* Scan possible input bits */ |
| 385 | for (b=0; b<2; b++) |
| 386 | { |
| 387 | int nae, ov, e; |
| 388 | uint8_t m; |
| 389 | |
| 390 | /* Next output and state */ |
| 391 | uint8_t out = code->next_output[s][b]; |
| 392 | uint8_t state = code->next_state[s][b]; |
| 393 | |
| 394 | /* New error for this path */ |
| 395 | nae = ae[s]; /* start from last error */ |
| 396 | m = 1 << (code->N - 1); /* mask for 'out' bit selection */ |
| 397 | |
| 398 | for (j=0; j<code->N; j++) { |
Sylvain Munaut | d4440d4 | 2011-11-24 16:04:58 +0100 | [diff] [blame] | 399 | int is = (int)in_sym[j]; |
| 400 | if (is) { |
| 401 | ov = (out & m) ? -127 : 127; /* sbit_t value for it */ |
| 402 | e = is - ov; /* raw error for this bit */ |
| 403 | nae += (e * e) >> 9; /* acc the squared/scaled value */ |
| 404 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 405 | m >>= 1; /* next mask bit */ |
| 406 | } |
| 407 | |
| 408 | /* Is it survivor ? */ |
| 409 | if (ae_next[state] > nae) { |
| 410 | ae_next[state] = nae; |
| 411 | state_history[(n_states * i) + state] = s; |
| 412 | } |
| 413 | } |
| 414 | } |
| 415 | |
| 416 | /* Copy accumulated error */ |
| 417 | memcpy(ae, ae_next, sizeof(unsigned int) * n_states); |
| 418 | } |
| 419 | |
| 420 | /* Update decoder state */ |
| 421 | decoder->p_idx = p_idx; |
| 422 | decoder->o_idx += n; |
| 423 | |
| 424 | return i_idx; |
| 425 | } |
| 426 | |
| 427 | int |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 428 | osmo_conv_decode_flush(struct osmo_conv_decoder *decoder, |
| 429 | const sbit_t *input) |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 430 | { |
| 431 | const struct osmo_conv_code *code = decoder->code; |
| 432 | |
| 433 | int i, s, j; |
| 434 | |
| 435 | int n_states; |
| 436 | unsigned int *ae; |
| 437 | unsigned int *ae_next; |
| 438 | uint8_t *state_history; |
| 439 | sbit_t *in_sym; |
| 440 | |
| 441 | int i_idx, p_idx; |
| 442 | |
| 443 | /* Prepare */ |
| 444 | n_states = decoder->n_states; |
| 445 | |
| 446 | ae = decoder->ae; |
| 447 | ae_next = decoder->ae_next; |
| 448 | state_history = &decoder->state_history[n_states * decoder->o_idx]; |
| 449 | |
| 450 | in_sym = alloca(sizeof(sbit_t) * code->N); |
| 451 | |
| 452 | i_idx = 0; |
| 453 | p_idx = decoder->p_idx; |
| 454 | |
| 455 | /* Scan the treillis */ |
| 456 | for (i=0; i<code->K-1; i++) |
| 457 | { |
| 458 | /* Reset next accumulated error */ |
| 459 | for (s=0; s<n_states; s++) { |
| 460 | ae_next[s] = MAX_AE; |
| 461 | } |
| 462 | |
| 463 | /* Get input */ |
| 464 | if (code->puncture) { |
| 465 | /* Hard way ... */ |
| 466 | for (j=0; j<code->N; j++) { |
| 467 | int idx = ((decoder->o_idx + i) * code->N) + j; |
| 468 | if (idx == code->puncture[p_idx]) { |
| 469 | in_sym[j] = 0; /* Undefined */ |
| 470 | p_idx++; |
| 471 | } else { |
| 472 | in_sym[j] = input[i_idx]; |
| 473 | i_idx++; |
| 474 | } |
| 475 | } |
| 476 | } else { |
| 477 | /* Easy, just copy N bits */ |
| 478 | memcpy(in_sym, &input[i_idx], code->N); |
| 479 | i_idx += code->N; |
| 480 | } |
| 481 | |
| 482 | /* Scan all state */ |
| 483 | for (s=0; s<n_states; s++) |
| 484 | { |
| 485 | int nae, ov, e; |
| 486 | uint8_t m; |
| 487 | |
| 488 | /* Next output and state */ |
| 489 | uint8_t out; |
| 490 | uint8_t state; |
| 491 | |
| 492 | if (code->next_term_output) { |
| 493 | out = code->next_term_output[s]; |
| 494 | state = code->next_term_state[s]; |
| 495 | } else { |
| 496 | out = code->next_output[s][0]; |
| 497 | state = code->next_state[s][0]; |
| 498 | } |
| 499 | |
| 500 | /* New error for this path */ |
| 501 | nae = ae[s]; /* start from last error */ |
| 502 | m = 1 << (code->N - 1); /* mask for 'out' bit selection */ |
| 503 | |
| 504 | for (j=0; j<code->N; j++) { |
Sylvain Munaut | 1dd7c84 | 2011-04-28 22:30:30 +0200 | [diff] [blame] | 505 | int is = (int)in_sym[j]; |
| 506 | if (is) { |
| 507 | ov = (out & m) ? -127 : 127; /* sbit_t value for it */ |
| 508 | e = is - ov; /* raw error for this bit */ |
| 509 | nae += (e * e) >> 9; /* acc the squared/scaled value */ |
| 510 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 511 | m >>= 1; /* next mask bit */ |
| 512 | } |
| 513 | |
| 514 | /* Is it survivor ? */ |
| 515 | if (ae_next[state] > nae) { |
| 516 | ae_next[state] = nae; |
| 517 | state_history[(n_states * i) + state] = s; |
| 518 | } |
| 519 | } |
| 520 | |
| 521 | /* Copy accumulated error */ |
| 522 | memcpy(ae, ae_next, sizeof(unsigned int) * n_states); |
| 523 | } |
| 524 | |
| 525 | /* Update decoder state */ |
| 526 | decoder->p_idx = p_idx; |
| 527 | decoder->o_idx += code->K - 1; |
| 528 | |
| 529 | return i_idx; |
| 530 | } |
| 531 | |
| 532 | int |
| 533 | osmo_conv_decode_get_output(struct osmo_conv_decoder *decoder, |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 534 | ubit_t *output, int has_flush, int end_state) |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 535 | { |
| 536 | const struct osmo_conv_code *code = decoder->code; |
| 537 | |
| 538 | int min_ae; |
| 539 | uint8_t min_state, cur_state; |
| 540 | int i, s, n; |
| 541 | |
| 542 | uint8_t *sh_ptr; |
| 543 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 544 | /* End state ? */ |
| 545 | if (end_state < 0) { |
| 546 | /* Find state with least error */ |
| 547 | min_ae = MAX_AE; |
| 548 | min_state = 0xff; |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 549 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 550 | for (s=0; s<decoder->n_states; s++) |
| 551 | { |
| 552 | if (decoder->ae[s] < min_ae) { |
| 553 | min_ae = decoder->ae[s]; |
| 554 | min_state = s; |
| 555 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 556 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 557 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 558 | if (min_state == 0xff) |
| 559 | return -1; |
| 560 | } else { |
| 561 | min_state = (uint8_t) end_state; |
| 562 | min_ae = decoder->ae[end_state]; |
| 563 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 564 | |
| 565 | /* Traceback */ |
| 566 | cur_state = min_state; |
| 567 | |
| 568 | n = decoder->o_idx; |
| 569 | |
| 570 | sh_ptr = &decoder->state_history[decoder->n_states * (n-1)]; |
| 571 | |
| 572 | /* No output for the K-1 termination input bits */ |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 573 | if (has_flush) { |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 574 | for (i=0; i<code->K-1; i++) { |
| 575 | cur_state = sh_ptr[cur_state]; |
| 576 | sh_ptr -= decoder->n_states; |
| 577 | } |
| 578 | n -= code->K - 1; |
| 579 | } |
| 580 | |
| 581 | /* Generate output backward */ |
| 582 | for (i=n-1; i>=0; i--) |
| 583 | { |
| 584 | min_state = cur_state; |
| 585 | cur_state = sh_ptr[cur_state]; |
| 586 | |
| 587 | sh_ptr -= decoder->n_states; |
| 588 | |
| 589 | if (code->next_state[cur_state][0] == min_state) |
| 590 | output[i] = 0; |
| 591 | else |
| 592 | output[i] = 1; |
| 593 | } |
| 594 | |
| 595 | return min_ae; |
| 596 | } |
| 597 | |
Neels Hofmeyr | 87e4550 | 2017-06-20 00:17:59 +0200 | [diff] [blame] | 598 | /*! All-in-one convolutional decoding function |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 599 | * \param[in] code description of convolutional code to be used |
| 600 | * \param[in] input array of soft bits (coded) |
| 601 | * \param[out] output array of unpacked bits (decoded) |
| 602 | * |
| 603 | * This is an all-in-one function, taking care of |
| 604 | * \ref osmo_conv_decode_init, \ref osmo_conv_decode_scan, |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 605 | * \ref osmo_conv_decode_flush, \ref osmo_conv_decode_get_output and |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 606 | * \ref osmo_conv_decode_deinit. |
| 607 | */ |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 608 | int |
| 609 | osmo_conv_decode(const struct osmo_conv_code *code, |
| 610 | const sbit_t *input, ubit_t *output) |
| 611 | { |
| 612 | struct osmo_conv_decoder decoder; |
| 613 | int rv, l; |
| 614 | |
Tom Tsou | 3553680 | 2016-11-24 19:24:32 +0700 | [diff] [blame] | 615 | /* Use accelerated implementation for supported codes */ |
| 616 | if ((code->N <= 4) && ((code->K == 5) || (code->K == 7))) |
| 617 | return osmo_conv_decode_acc(code, input, output); |
| 618 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 619 | osmo_conv_decode_init(&decoder, code, 0, 0); |
| 620 | |
| 621 | if (code->term == CONV_TERM_TAIL_BITING) { |
| 622 | osmo_conv_decode_scan(&decoder, input, code->len); |
| 623 | osmo_conv_decode_rewind(&decoder); |
| 624 | } |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 625 | |
| 626 | l = osmo_conv_decode_scan(&decoder, input, code->len); |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 627 | |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 628 | if (code->term == CONV_TERM_FLUSH) |
Vadim Yanitskiy | 6e6978a | 2017-06-12 03:47:34 +0700 | [diff] [blame] | 629 | osmo_conv_decode_flush(&decoder, &input[l]); |
Sylvain Munaut | 297d13f | 2011-11-24 17:46:58 +0100 | [diff] [blame] | 630 | |
| 631 | rv = osmo_conv_decode_get_output(&decoder, output, |
| 632 | code->term == CONV_TERM_FLUSH, /* has_flush */ |
| 633 | code->term == CONV_TERM_FLUSH ? 0 : -1 /* end_state */ |
| 634 | ); |
Sylvain Munaut | 19dc5c9 | 2011-04-23 16:09:19 +0200 | [diff] [blame] | 635 | |
| 636 | osmo_conv_decode_deinit(&decoder); |
| 637 | |
| 638 | return rv; |
| 639 | } |
Harald Welte | ba6988b | 2011-08-17 12:46:48 +0200 | [diff] [blame] | 640 | |
Sylvain Munaut | dca7d2c | 2012-04-18 21:53:23 +0200 | [diff] [blame] | 641 | /*! @} */ |