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/*
* Accelerated Viterbi decoder implementation
* for generic architectures without SSE support
*
* 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 <stdint.h>
#include <string.h>
/* Add-Compare-Select (ACS-Butterfly)
* Compute 4 accumulated path metrics and 4 path selections. Note that path
* selections are store as -1 and 0 rather than 0 and 1. This is to match
* the output format of the SSE packed compare instruction 'pmaxuw'.
*/
static void acs_butterfly(int state, int num_states,
int16_t metric, int16_t *sum,
int16_t *new_sum, int16_t *path)
{
int state0, state1;
int sum0, sum1, sum2, sum3;
state0 = *(sum + (2 * state + 0));
state1 = *(sum + (2 * state + 1));
sum0 = state0 + metric;
sum1 = state1 - metric;
sum2 = state0 - metric;
sum3 = state1 + metric;
if (sum0 >= sum1) {
*new_sum = sum0;
*path = -1;
} else {
*new_sum = sum1;
*path = 0;
}
if (sum2 >= sum3) {
*(new_sum + num_states / 2) = sum2;
*(path + num_states / 2) = -1;
} else {
*(new_sum + num_states / 2) = sum3;
*(path + num_states / 2) = 0;
}
}
/* Branch metrics unit N=2 */
static void gen_branch_metrics_n2(int num_states, const int8_t *seq,
const int16_t *out, int16_t *metrics)
{
int i;
for (i = 0; i < num_states / 2; i++) {
metrics[i] = seq[0] * out[2 * i + 0] +
seq[1] * out[2 * i + 1];
}
}
/* Branch metrics unit N=3 */
static void gen_branch_metrics_n3(int num_states, const int8_t *seq,
const int16_t *out, int16_t *metrics)
{
int i;
for (i = 0; i < num_states / 2; i++) {
metrics[i] = seq[0] * out[4 * i + 0] +
seq[1] * out[4 * i + 1] +
seq[2] * out[4 * i + 2];
}
}
/* Branch metrics unit N=4 */
static void gen_branch_metrics_n4(int num_states, const int8_t *seq,
const int16_t *out, int16_t *metrics)
{
int i;
for (i = 0; i < num_states / 2; i++) {
metrics[i] = seq[0] * out[4 * i + 0] +
seq[1] * out[4 * i + 1] +
seq[2] * out[4 * i + 2] +
seq[3] * out[4 * i + 3];
}
}
/* Path metric unit */
static void gen_path_metrics(int num_states, int16_t *sums,
int16_t *metrics, int16_t *paths, int norm)
{
int i;
int16_t min;
int16_t new_sums[num_states];
for (i = 0; i < num_states / 2; i++)
acs_butterfly(i, num_states, metrics[i],
sums, &new_sums[i], &paths[i]);
if (norm) {
min = new_sums[0];
for (i = 1; i < num_states; i++)
if (new_sums[i] < min)
min = new_sums[i];
for (i = 0; i < num_states; i++)
new_sums[i] -= min;
}
memcpy(sums, new_sums, num_states * sizeof(int16_t));
}
/* Not-aligned Memory Allocator */
__attribute__ ((visibility("hidden")))
int16_t *osmo_conv_gen_vdec_malloc(size_t n)
{
return (int16_t *) malloc(sizeof(int16_t) * n);
}
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_vdec_free(int16_t *ptr)
{
free(ptr);
}
/* 16-state branch-path metrics units (K=5) */
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_metrics_k5_n2(const int8_t *seq, const int16_t *out,
int16_t *sums, int16_t *paths, int norm)
{
int16_t metrics[8];
gen_branch_metrics_n2(16, seq, out, metrics);
gen_path_metrics(16, sums, metrics, paths, norm);
}
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_metrics_k5_n3(const int8_t *seq, const int16_t *out,
int16_t *sums, int16_t *paths, int norm)
{
int16_t metrics[8];
gen_branch_metrics_n3(16, seq, out, metrics);
gen_path_metrics(16, sums, metrics, paths, norm);
}
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_metrics_k5_n4(const int8_t *seq, const int16_t *out,
int16_t *sums, int16_t *paths, int norm)
{
int16_t metrics[8];
gen_branch_metrics_n4(16, seq, out, metrics);
gen_path_metrics(16, sums, metrics, paths, norm);
}
/* 64-state branch-path metrics units (K=7) */
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_metrics_k7_n2(const int8_t *seq, const int16_t *out,
int16_t *sums, int16_t *paths, int norm)
{
int16_t metrics[32];
gen_branch_metrics_n2(64, seq, out, metrics);
gen_path_metrics(64, sums, metrics, paths, norm);
}
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_metrics_k7_n3(const int8_t *seq, const int16_t *out,
int16_t *sums, int16_t *paths, int norm)
{
int16_t metrics[32];
gen_branch_metrics_n3(64, seq, out, metrics);
gen_path_metrics(64, sums, metrics, paths, norm);
}
__attribute__ ((visibility("hidden")))
void osmo_conv_gen_metrics_k7_n4(const int8_t *seq, const int16_t *out,
int16_t *sums, int16_t *paths, int norm)
{
int16_t metrics[32];
gen_branch_metrics_n4(64, seq, out, metrics);
gen_path_metrics(64, sums, metrics, paths, norm);
}
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