| /* |
| * Viterbi decoder |
| * |
| * Copyright (C) 2013, 2014 Thomas Tsou <tom@tsou.cc> |
| * |
| * All Rights Reserved |
| * |
| * This program is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; either version 2 of the License, or |
| * (at your option) any later version. |
| * |
| * This program is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| * GNU General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License along |
| * with this program; if not, write to the Free Software Foundation, Inc., |
| * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| */ |
| |
| #include <stdlib.h> |
| #include <string.h> |
| #include <errno.h> |
| |
| #include <osmocom/core/conv.h> |
| #include "config.h" |
| |
| #define BIT2NRZ(REG,N) (((REG >> N) & 0x01) * 2 - 1) * -1 |
| #define NUM_STATES(K) (K == 7 ? 64 : 16) |
| #define SSE_ALIGN 16 |
| |
| /* Forward Metric Units */ |
| void osmo_conv_gen_metrics_k5_n2(const int8_t *seq, const int16_t *out, |
| int16_t *sums, int16_t *paths, int norm); |
| void osmo_conv_gen_metrics_k5_n3(const int8_t *seq, const int16_t *out, |
| int16_t *sums, int16_t *paths, int norm); |
| void osmo_conv_gen_metrics_k5_n4(const int8_t *seq, const int16_t *out, |
| int16_t *sums, int16_t *paths, int norm); |
| void osmo_conv_gen_metrics_k7_n2(const int8_t *seq, const int16_t *out, |
| int16_t *sums, int16_t *paths, int norm); |
| void osmo_conv_gen_metrics_k7_n3(const int8_t *seq, const int16_t *out, |
| int16_t *sums, int16_t *paths, int norm); |
| void osmo_conv_gen_metrics_k7_n4(const int8_t *seq, const int16_t *out, |
| int16_t *sums, int16_t *paths, int norm); |
| |
| /* Trellis State |
| * state - Internal lshift register value |
| * prev - Register values of previous 0 and 1 states |
| */ |
| struct vstate { |
| unsigned state; |
| unsigned prev[2]; |
| }; |
| |
| /* Trellis Object |
| * num_states - Number of states in the trellis |
| * sums - Accumulated path metrics |
| * outputs - Trellis output values |
| * vals - Input value that led to each state |
| */ |
| struct vtrellis { |
| int num_states; |
| int16_t *sums; |
| int16_t *outputs; |
| uint8_t *vals; |
| }; |
| |
| /* Viterbi Decoder |
| * n - Code order |
| * k - Constraint length |
| * len - Horizontal length of trellis |
| * recursive - Set to '1' if the code is recursive |
| * intrvl - Normalization interval |
| * trellis - Trellis object |
| * punc - Puncturing sequence |
| * paths - Trellis paths |
| */ |
| struct vdecoder { |
| int n; |
| int k; |
| int len; |
| int recursive; |
| int intrvl; |
| struct vtrellis *trellis; |
| int *punc; |
| int16_t **paths; |
| |
| void (*metric_func)(const int8_t *, const int16_t *, |
| int16_t *, int16_t *, int); |
| }; |
| |
| /* Aligned Memory Allocator |
| * SSE requires 16-byte memory alignment. We store relevant trellis values |
| * (accumulated sums, outputs, and path decisions) as 16 bit signed integers |
| * so the allocated memory is casted as such. |
| */ |
| static int16_t *vdec_malloc(size_t n) |
| { |
| #ifdef HAVE_SSE3 |
| return (int16_t *) memalign(SSE_ALIGN, sizeof(int16_t) * n); |
| #else |
| return (int16_t *) malloc(sizeof(int16_t) * n); |
| #endif |
| } |
| |
| /* Accessor calls */ |
| static inline int conv_code_recursive(const struct osmo_conv_code *code) |
| { |
| return code->next_term_output ? 1 : 0; |
| } |
| |
| /* Left shift and mask for finding the previous state */ |
| static unsigned vstate_lshift(unsigned reg, int k, int val) |
| { |
| unsigned mask; |
| |
| if (k == 5) |
| mask = 0x0e; |
| else if (k == 7) |
| mask = 0x3e; |
| else |
| mask = 0; |
| |
| return ((reg << 1) & mask) | val; |
| } |
| |
| /* Bit endian manipulators */ |
| static inline unsigned bitswap2(unsigned v) |
| { |
| return ((v & 0x02) >> 1) | ((v & 0x01) << 1); |
| } |
| |
| static inline unsigned bitswap3(unsigned v) |
| { |
| return ((v & 0x04) >> 2) | ((v & 0x02) >> 0) | |
| ((v & 0x01) << 2); |
| } |
| |
| static inline unsigned bitswap4(unsigned v) |
| { |
| return ((v & 0x08) >> 3) | ((v & 0x04) >> 1) | |
| ((v & 0x02) << 1) | ((v & 0x01) << 3); |
| } |
| |
| static inline unsigned bitswap5(unsigned v) |
| { |
| return ((v & 0x10) >> 4) | ((v & 0x08) >> 2) | ((v & 0x04) >> 0) | |
| ((v & 0x02) << 2) | ((v & 0x01) << 4); |
| } |
| |
| static inline unsigned bitswap6(unsigned v) |
| { |
| return ((v & 0x20) >> 5) | ((v & 0x10) >> 3) | ((v & 0x08) >> 1) | |
| ((v & 0x04) << 1) | ((v & 0x02) << 3) | ((v & 0x01) << 5); |
| } |
| |
| static unsigned bitswap(unsigned v, unsigned n) |
| { |
| switch (n) { |
| case 1: |
| return v; |
| case 2: |
| return bitswap2(v); |
| case 3: |
| return bitswap3(v); |
| case 4: |
| return bitswap4(v); |
| case 5: |
| return bitswap5(v); |
| case 6: |
| return bitswap6(v); |
| default: |
| return 0; |
| } |
| } |
| |
| /* Generate non-recursive state output from generator state table |
| * Note that the shift register moves right (i.e. the most recent bit is |
| * shifted into the register at k-1 bit of the register), which is typical |
| * textbook representation. The API transition table expects the most recent |
| * bit in the low order bit, or left shift. A bitswap operation is required |
| * to accommodate the difference. |
| */ |
| static unsigned gen_output(struct vstate *state, int val, |
| const struct osmo_conv_code *code) |
| { |
| unsigned out, prev; |
| |
| prev = bitswap(state->prev[0], code->K - 1); |
| out = code->next_output[prev][val]; |
| out = bitswap(out, code->N); |
| |
| return out; |
| } |
| |
| /* Populate non-recursive trellis state |
| * For a given state defined by the k-1 length shift register, find the |
| * value of the input bit that drove the trellis to that state. Also |
| * generate the N outputs of the generator polynomial at that state. |
| */ |
| static int gen_state_info(uint8_t *val, unsigned reg, |
| int16_t *output, const struct osmo_conv_code *code) |
| { |
| int i; |
| unsigned out; |
| struct vstate state; |
| |
| /* Previous '0' state */ |
| state.state = reg; |
| state.prev[0] = vstate_lshift(reg, code->K, 0); |
| state.prev[1] = vstate_lshift(reg, code->K, 1); |
| |
| *val = (reg >> (code->K - 2)) & 0x01; |
| |
| /* Transition output */ |
| out = gen_output(&state, *val, code); |
| |
| /* Unpack to NRZ */ |
| for (i = 0; i < code->N; i++) |
| output[i] = BIT2NRZ(out, i); |
| |
| return 0; |
| } |
| |
| /* Generate recursive state output from generator state table */ |
| static unsigned gen_recursive_output(struct vstate *state, |
| uint8_t *val, unsigned reg, |
| const struct osmo_conv_code *code, int pos) |
| { |
| int val0, val1; |
| unsigned out, prev; |
| |
| /* Previous '0' state */ |
| prev = vstate_lshift(reg, code->K, 0); |
| prev = bitswap(prev, code->K - 1); |
| |
| /* Input value */ |
| val0 = (reg >> (code->K - 2)) & 0x01; |
| val1 = (code->next_term_output[prev] >> pos) & 0x01; |
| *val = val0 == val1 ? 0 : 1; |
| |
| /* Wrapper for osmocom state access */ |
| prev = bitswap(state->prev[0], code->K - 1); |
| |
| /* Compute the transition output */ |
| out = code->next_output[prev][*val]; |
| out = bitswap(out, code->N); |
| |
| return out; |
| } |
| |
| /* Populate recursive trellis state |
| * The bit position of the systematic bit is not explicitly marked by the |
| * API, so it must be extracted from the generator table. Otherwise, |
| * populate the trellis similar to the non-recursive version. |
| * Non-systematic recursive codes are not supported. |
| */ |
| static int gen_recursive_state_info(uint8_t *val, |
| unsigned reg, int16_t *output, const struct osmo_conv_code *code) |
| { |
| int i, j, pos = -1; |
| int ns = NUM_STATES(code->K); |
| unsigned out; |
| struct vstate state; |
| |
| /* Previous '0' and '1' states */ |
| state.state = reg; |
| state.prev[0] = vstate_lshift(reg, code->K, 0); |
| state.prev[1] = vstate_lshift(reg, code->K, 1); |
| |
| /* Find recursive bit location */ |
| for (i = 0; i < code->N; i++) { |
| for (j = 0; j < ns; j++) { |
| if ((code->next_output[j][0] >> i) & 0x01) |
| break; |
| } |
| |
| if (j == ns) { |
| pos = i; |
| break; |
| } |
| } |
| |
| /* Non-systematic recursive code not supported */ |
| if (pos < 0) |
| return -EPROTO; |
| |
| /* Transition output */ |
| out = gen_recursive_output(&state, val, reg, code, pos); |
| |
| /* Unpack to NRZ */ |
| for (i = 0; i < code->N; i++) |
| output[i] = BIT2NRZ(out, i); |
| |
| return 0; |
| } |
| |
| /* Release the trellis */ |
| static void free_trellis(struct vtrellis *trellis) |
| { |
| if (!trellis) |
| return; |
| |
| free(trellis->vals); |
| free(trellis->outputs); |
| free(trellis->sums); |
| free(trellis); |
| } |
| |
| /* Allocate and initialize the trellis object |
| * Initialization consists of generating the outputs and output value of a |
| * given state. Due to trellis symmetry and anti-symmetry, only one of the |
| * transition paths is utilized by the butterfly operation in the forward |
| * recursion, so only one set of N outputs is required per state variable. |
| */ |
| static struct vtrellis *generate_trellis(const struct osmo_conv_code *code) |
| { |
| int i, rc = -1; |
| struct vtrellis *trellis; |
| int16_t *outputs; |
| |
| int ns = NUM_STATES(code->K); |
| int recursive = conv_code_recursive(code); |
| int olen = (code->N == 2) ? 2 : 4; |
| |
| trellis = (struct vtrellis *) calloc(1, sizeof(struct vtrellis)); |
| trellis->num_states = ns; |
| trellis->sums = vdec_malloc(ns); |
| trellis->outputs = vdec_malloc(ns * olen); |
| trellis->vals = (uint8_t *) malloc(ns * sizeof(uint8_t)); |
| |
| if (!trellis->sums || !trellis->outputs) |
| goto fail; |
| |
| /* Populate the trellis state objects */ |
| for (i = 0; i < ns; i++) { |
| outputs = &trellis->outputs[olen * i]; |
| if (recursive) { |
| rc = gen_recursive_state_info(&trellis->vals[i], |
| i, outputs, code); |
| } else { |
| rc = gen_state_info(&trellis->vals[i], |
| i, outputs, code); |
| } |
| } |
| |
| if (rc < 0) |
| goto fail; |
| |
| return trellis; |
| |
| fail: |
| free_trellis(trellis); |
| return NULL; |
| } |
| |
| /* Reset decoder |
| * Set accumulated path metrics to zero. For termination other than |
| * tail-biting, initialize the zero state as the encoder starting state. |
| * Initialize with the maximum accumulated sum at length equal to the |
| * constraint length. |
| */ |
| static void reset_decoder(struct vdecoder *dec, int term) |
| { |
| int ns = dec->trellis->num_states; |
| |
| memset(dec->trellis->sums, 0, sizeof(int16_t) * ns); |
| |
| if (term != CONV_TERM_TAIL_BITING) |
| dec->trellis->sums[0] = INT8_MAX * dec->n * dec->k; |
| } |
| |
| static void _traceback(struct vdecoder *dec, |
| unsigned state, uint8_t *out, int len) |
| { |
| int i; |
| unsigned path; |
| |
| for (i = len - 1; i >= 0; i--) { |
| path = dec->paths[i][state] + 1; |
| out[i] = dec->trellis->vals[state]; |
| state = vstate_lshift(state, dec->k, path); |
| } |
| } |
| |
| static void _traceback_rec(struct vdecoder *dec, |
| unsigned state, uint8_t *out, int len) |
| { |
| int i; |
| unsigned path; |
| |
| for (i = len - 1; i >= 0; i--) { |
| path = dec->paths[i][state] + 1; |
| out[i] = path ^ dec->trellis->vals[state]; |
| state = vstate_lshift(state, dec->k, path); |
| } |
| } |
| |
| /* Traceback and generate decoded output |
| * Find the largest accumulated path metric at the final state except for |
| * the zero terminated case, where we assume the final state is always zero. |
| */ |
| static int traceback(struct vdecoder *dec, uint8_t *out, int term, int len) |
| { |
| int i, sum, max = -1; |
| unsigned path, state = 0; |
| |
| if (term != CONV_TERM_FLUSH) { |
| for (i = 0; i < dec->trellis->num_states; i++) { |
| sum = dec->trellis->sums[i]; |
| if (sum > max) { |
| max = sum; |
| state = i; |
| } |
| } |
| |
| if (max < 0) |
| return -EPROTO; |
| } |
| |
| for (i = dec->len - 1; i >= len; i--) { |
| path = dec->paths[i][state] + 1; |
| state = vstate_lshift(state, dec->k, path); |
| } |
| |
| if (dec->recursive) |
| _traceback_rec(dec, state, out, len); |
| else |
| _traceback(dec, state, out, len); |
| |
| return 0; |
| } |
| |
| /* Release decoder object */ |
| static void free_vdec(struct vdecoder *dec) |
| { |
| if (!dec) |
| return; |
| |
| free(dec->paths[0]); |
| free(dec->paths); |
| free_trellis(dec->trellis); |
| free(dec); |
| } |
| |
| /* Allocate decoder object |
| * Subtract the constraint length K on the normalization interval to |
| * accommodate the initialization path metric at state zero. |
| */ |
| static struct vdecoder *alloc_vdec(const struct osmo_conv_code *code) |
| { |
| int i, ns; |
| struct vdecoder *dec; |
| |
| ns = NUM_STATES(code->K); |
| |
| dec = (struct vdecoder *) calloc(1, sizeof(struct vdecoder)); |
| dec->n = code->N; |
| dec->k = code->K; |
| dec->recursive = conv_code_recursive(code); |
| dec->intrvl = INT16_MAX / (dec->n * INT8_MAX) - dec->k; |
| |
| if (dec->k == 5) { |
| switch (dec->n) { |
| case 2: |
| dec->metric_func = osmo_conv_gen_metrics_k5_n2; |
| break; |
| case 3: |
| dec->metric_func = osmo_conv_gen_metrics_k5_n3; |
| break; |
| case 4: |
| dec->metric_func = osmo_conv_gen_metrics_k5_n4; |
| break; |
| default: |
| goto fail; |
| } |
| } else if (dec->k == 7) { |
| switch (dec->n) { |
| case 2: |
| dec->metric_func = osmo_conv_gen_metrics_k7_n2; |
| break; |
| case 3: |
| dec->metric_func = osmo_conv_gen_metrics_k7_n3; |
| break; |
| case 4: |
| dec->metric_func = osmo_conv_gen_metrics_k7_n4; |
| break; |
| default: |
| goto fail; |
| } |
| } else { |
| goto fail; |
| } |
| |
| if (code->term == CONV_TERM_FLUSH) |
| dec->len = code->len + code->K - 1; |
| else |
| dec->len = code->len; |
| |
| dec->trellis = generate_trellis(code); |
| if (!dec->trellis) |
| goto fail; |
| |
| dec->paths = (int16_t **) malloc(sizeof(int16_t *) * dec->len); |
| dec->paths[0] = vdec_malloc(ns * dec->len); |
| for (i = 1; i < dec->len; i++) |
| dec->paths[i] = &dec->paths[0][i * ns]; |
| |
| return dec; |
| |
| fail: |
| free_vdec(dec); |
| return NULL; |
| } |
| |
| /* Depuncture sequence with nagative value terminated puncturing matrix */ |
| static int depuncture(const int8_t *in, const int *punc, int8_t *out, int len) |
| { |
| int i, n = 0, m = 0; |
| |
| for (i = 0; i < len; i++) { |
| if (i == punc[n]) { |
| out[i] = 0; |
| n++; |
| continue; |
| } |
| |
| out[i] = in[m++]; |
| } |
| |
| return 0; |
| } |
| |
| /* Forward trellis recursion |
| * Generate branch metrics and path metrics with a combined function. Only |
| * accumulated path metric sums and path selections are stored. Normalize on |
| * the interval specified by the decoder. |
| */ |
| static void forward_traverse(struct vdecoder *dec, const int8_t *seq) |
| { |
| struct vtrellis *trellis = dec->trellis; |
| int i; |
| |
| for (i = 0; i < dec->len; i++) { |
| dec->metric_func(&seq[dec->n * i], |
| trellis->outputs, |
| trellis->sums, |
| dec->paths[i], |
| !(i % dec->intrvl)); |
| } |
| } |
| |
| /* Convolutional decode with a decoder object |
| * Initial puncturing run if necessary followed by the forward recursion. |
| * For tail-biting perform a second pass before running the backward |
| * traceback operation. |
| */ |
| static int conv_decode(struct vdecoder *dec, const int8_t *seq, |
| const int *punc, uint8_t *out, int len, int term) |
| { |
| int8_t depunc[dec->len * dec->n]; |
| |
| reset_decoder(dec, term); |
| |
| if (punc) { |
| depuncture(seq, punc, depunc, dec->len * dec->n); |
| seq = depunc; |
| } |
| |
| /* Propagate through the trellis with interval normalization */ |
| forward_traverse(dec, seq); |
| |
| if (term == CONV_TERM_TAIL_BITING) |
| forward_traverse(dec, seq); |
| |
| return traceback(dec, out, term, len); |
| } |
| |
| /* All-in-one Viterbi decoding */ |
| int osmo_conv_decode_acc(const struct osmo_conv_code *code, |
| const sbit_t *input, ubit_t *output) |
| { |
| int rc; |
| struct vdecoder *vdec; |
| |
| if ((code->N < 2) || (code->N > 4) || (code->len < 1) || |
| ((code->K != 5) && (code->K != 7))) |
| return -EINVAL; |
| |
| vdec = alloc_vdec(code); |
| if (!vdec) |
| return -EFAULT; |
| |
| rc = conv_decode(vdec, input, code->puncture, |
| output, code->len, code->term); |
| |
| free_vdec(vdec); |
| |
| return rc; |
| } |