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srsLTE
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srsLTE/lib/src/phy/fec/turbodecoder_gen.c

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/*
* Copyright 2013-2020 Software Radio Systems Limited
*
* This file is part of srsLTE.
*
* srsLTE is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of
* the License, or (at your option) any later version.
*
* srsLTE 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 Affero General Public License for more details.
*
* A copy of the GNU Affero General Public License can be found in
* the LICENSE file in the top-level directory of this distribution
* and at http://www.gnu.org/licenses/.
*
*/
#include <math.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include "srslte/phy/fec/turbodecoder_gen.h"
#include "srslte/phy/utils/vector.h"
#define NUMSTATES 8
#define NINPUTS 2
#define TAIL 3
#define TOTALTAIL 12
#define INF 10000
#define debug_enabled 0
#if debug_enabled
#define debug_state \
printf("k=%5d, in=%5d, pa=%3d, out=%5d, alpha=", k, x, parity[k - 1], out); \
srslte_vec_fprint_s(stdout, alpha, 8); \
printf(", beta="); \
srslte_vec_fprint_s(stdout, &beta[8 * (k)], 8); \
printf("\n");
#else
#define debug_state
#endif
/************************************************
*
* MAP_GEN is the MAX-LOG-MAP generic implementation of the
* Decoder
*
************************************************/
static void map_gen_beta(tdec_gen_t* s, int16_t* input, int16_t* app, int16_t* parity, uint32_t long_cb)
{
int16_t m_b[8], new[8], old[8];
int16_t x, y, xy;
int k;
uint32_t end = long_cb + SRSLTE_TCOD_RATE;
int16_t* beta = s->beta;
uint32_t i;
for (i = 0; i < 8; i++) {
old[i] = beta[8 * (end) + i];
}
for (k = end - 1; k >= 0; k--) {
x = input[k];
if (app && k < long_cb) {
x += app[k];
}
y = parity[k];
xy = x + y;
m_b[0] = old[4] + xy;
m_b[1] = old[4];
m_b[2] = old[5] + y;
m_b[3] = old[5] + x;
m_b[4] = old[6] + x;
m_b[5] = old[6] + y;
m_b[6] = old[7];
m_b[7] = old[7] + xy;
new[0] = old[0];
new[1] = old[0] + xy;
new[2] = old[1] + x;
new[3] = old[1] + y;
new[4] = old[2] + y;
new[5] = old[2] + x;
new[6] = old[3] + xy;
new[7] = old[3];
for (i = 0; i < 8; i++) {
if (m_b[i] > new[i])
new[i] = m_b[i];
old[i] = new[i];
beta[8 * k + i] = old[i];
}
if ((k % 4) == 0 && k < long_cb) {
for (i = 1; i < 8; i++) {
old[i] -= old[0];
}
old[0] = 0;
}
}
}
static void
map_gen_alpha(tdec_gen_t* s, int16_t* input, int16_t* app, int16_t* parity, int16_t* output, uint32_t long_cb)
{
int16_t m_b[8], new[8], old[8], max1[8], max0[8];
int16_t m1, m0;
int16_t x, y, xy;
int16_t out;
uint32_t k;
uint32_t end = long_cb;
int16_t* beta = s->beta;
uint32_t i;
old[0] = 0;
for (i = 1; i < 8; i++) {
old[i] = -INF;
}
#if debug_enabled
int16_t alpha[8];
#endif
for (k = 1; k < end + 1; k++) {
x = input[k - 1];
if (app) {
x += app[k - 1];
}
y = parity[k - 1];
xy = x + y;
#if debug_enabled
memcpy(alpha, old, sizeof(int16_t) * 8);
#endif
m_b[0] = old[0];
m_b[1] = old[3] + y;
m_b[2] = old[4] + y;
m_b[3] = old[7];
m_b[4] = old[1];
m_b[5] = old[2] + y;
m_b[6] = old[5] + y;
m_b[7] = old[6];
new[0] = old[1] + xy;
new[1] = old[2] + x;
new[2] = old[5] + x;
new[3] = old[6] + xy;
new[4] = old[0] + xy;
new[5] = old[3] + x;
new[6] = old[4] + x;
new[7] = old[7] + xy;
for (i = 0; i < 8; i++) {
max0[i] = m_b[i] + beta[8 * k + i];
max1[i] = new[i] + beta[8 * k + i];
}
m1 = max1[0];
m0 = max0[0];
for (i = 1; i < 8; i++) {
if (max1[i] > m1)
m1 = max1[i];
if (max0[i] > m0)
m0 = max0[i];
}
for (i = 0; i < 8; i++) {
if (m_b[i] > new[i])
new[i] = m_b[i];
old[i] = new[i];
}
if ((k % 4) == 0) {
for (i = 1; i < 8; i++) {
old[i] -= old[0];
}
old[0] = 0;
}
out = m1 - m0;
output[k - 1] = out;
debug_state;
}
}
int tdec_gen_init(void** hh, uint32_t max_long_cb)
{
*hh = calloc(1, sizeof(tdec_gen_t));
tdec_gen_t* h = (tdec_gen_t*)*hh;
h->beta = srslte_vec_i16_malloc((max_long_cb + SRSLTE_TCOD_TOTALTAIL + 1) * NUMSTATES);
if (!h->beta) {
perror("srslte_vec_malloc");
return -1;
}
h->max_long_cb = max_long_cb;
return 1;
}
void tdec_gen_free(void* hh)
{
tdec_gen_t* h = (tdec_gen_t*)hh;
if (h) {
if (h->beta) {
free(h->beta);
}
free(h);
}
}
void tdec_gen_dec(void* hh, int16_t* input, int16_t* app, int16_t* parity, int16_t* output, uint32_t long_cb)
{
tdec_gen_t* h = (tdec_gen_t*)hh;
h->beta[(long_cb + TAIL) * NUMSTATES] = 0;
for (uint32_t k = 1; k < NUMSTATES; k++)
h->beta[(long_cb + TAIL) * NUMSTATES + k] = -INF;
map_gen_beta(h, input, app, parity, long_cb);
map_gen_alpha(h, input, app, parity, output, long_cb);
}
void tdec_gen_extract_input(int16_t* input,
int16_t* syst,
int16_t* app2,
int16_t* parity0,
int16_t* parity1,
uint32_t long_cb)
{
// Prepare systematic and parity bits for MAP DEC #1
for (uint32_t i = 0; i < long_cb; i++) {
syst[i] = input[SRSLTE_TCOD_RATE * i];
parity0[i] = input[SRSLTE_TCOD_RATE * i + 1];
parity1[i] = input[SRSLTE_TCOD_RATE * i + 2];
}
for (uint32_t i = long_cb; i < long_cb + SRSLTE_TCOD_RATE; i++) {
syst[i] = input[SRSLTE_TCOD_RATE * long_cb + NINPUTS * (i - long_cb)];
parity0[i] = input[SRSLTE_TCOD_RATE * long_cb + NINPUTS * (i - long_cb) + 1];
app2[i] = input[SRSLTE_TCOD_RATE * long_cb + NINPUTS * SRSLTE_TCOD_RATE + NINPUTS * (i - long_cb)];
parity1[i] = input[SRSLTE_TCOD_RATE * long_cb + NINPUTS * SRSLTE_TCOD_RATE + NINPUTS * (i - long_cb) + 1];
}
}
void tdec_gen_decision_byte(int16_t* app1, uint8_t* output, uint32_t long_cb)
{
uint8_t mask[8] = {0x80, 0x40, 0x20, 0x10, 0x8, 0x4, 0x2, 0x1};
// long_cb is always byte aligned
for (uint32_t i = 0; i < long_cb / 8; i++) {
uint8_t out0 = app1[8 * i + 0] > 0 ? mask[0] : 0;
uint8_t out1 = app1[8 * i + 1] > 0 ? mask[1] : 0;
uint8_t out2 = app1[8 * i + 2] > 0 ? mask[2] : 0;
uint8_t out3 = app1[8 * i + 3] > 0 ? mask[3] : 0;
uint8_t out4 = app1[8 * i + 4] > 0 ? mask[4] : 0;
uint8_t out5 = app1[8 * i + 5] > 0 ? mask[5] : 0;
uint8_t out6 = app1[8 * i + 6] > 0 ? mask[6] : 0;
uint8_t out7 = app1[8 * i + 7] > 0 ? mask[7] : 0;
output[i] = out0 | out1 | out2 | out3 | out4 | out5 | out6 | out7;
}
}
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