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/* -*- c -*- */
/*
* Copyright 2015-2019 Miklos Maroti
* Copyright 2019 Daniel Estevez <daniel@destevez.net> (reentrant version)
*
* This file is part of gr-satellites
*
* SPDX-License-Identifier: GPL-3.0-or-later
*
*/
#include "ra_decoder_gen.h"
#include "ra_lfsr.h"
#include <assert.h>
#include <float.h>
#include <math.h>
#include <stdbool.h>
/* --- REPEAT ACCUMULATE GENERIC DECODER --- */
void ra_prepare_gen(struct ra_context* ctx, float* softbits)
{
int index;
for (index = 0; index < ctx->ra_data_length * RA_BITCOUNT; index++)
ctx->ra_dataword_gen[index] = 0.0f;
for (index = 0; index < ctx->ra_code_length * RA_BITCOUNT; index++)
ctx->ra_codeword_gen[index] = softbits[index];
}
static inline float ra_llr_min(float a, float b)
{
float c;
c = a * b;
a = fabsf(a);
b = fabsf(b);
a = a < b ? a : b;
return copysignf(a, c);
}
void ra_improve_gen(struct ra_context* ctx, float* codeword, int puncture, bool half)
{
int index, bit, pos = 0; /* to avoid pos uninitialized warning */
float accu[RA_BITCOUNT];
float data, left;
assert(ctx->ra_data_length > 0); /* to avoid pos uninitialized warning */
for (bit = 0; bit < RA_BITCOUNT; bit++)
accu[bit] = FLT_MAX;
for (index = 0; index < ctx->ra_data_length; index++) {
pos = ra_lfsr_next(ctx);
for (bit = 0; bit < RA_BITCOUNT; bit++) {
data = ctx->ra_dataword_gen[pos * RA_BITCOUNT + bit];
ctx->ra_forward_gen[index * RA_BITCOUNT + bit] = accu[bit];
accu[bit] = ra_llr_min(accu[bit], data);
}
if ((index + 1) % puncture == 0) {
for (bit = 0; bit < RA_BITCOUNT; bit++)
accu[bit] += *(codeword++);
}
data = accu[0];
for (bit = 0; bit < RA_BITCOUNT - 1; bit++)
accu[bit] = accu[bit + 1];
accu[RA_BITCOUNT - 1] = data;
}
if (ctx->ra_data_length % puncture != 0) {
for (bit = 0; bit < RA_BITCOUNT; bit++) {
data = codeword[(bit + 1) % RA_BITCOUNT];
accu[bit] = accu[bit] + data + data;
}
}
for (index = ctx->ra_data_length - 1; index >= 0; index--) {
data = accu[RA_BITCOUNT - 1];
for (bit = RA_BITCOUNT - 1; bit >= 1; bit--)
accu[bit] = accu[bit - 1];
accu[0] = data;
if ((index + 1) % puncture == 0) {
for (bit = RA_BITCOUNT - 1; bit >= 0; bit--)
accu[bit] += *(--codeword);
}
for (bit = 0; bit < RA_BITCOUNT; bit++) {
left = ctx->ra_forward_gen[index * RA_BITCOUNT + bit];
left = ra_llr_min(left, accu[bit]);
data = ctx->ra_dataword_gen[pos * RA_BITCOUNT + bit];
accu[bit] = ra_llr_min(accu[bit], data);
if (half)
data *= 0.5f;
left += data;
ctx->ra_dataword_gen[pos * RA_BITCOUNT + bit] = left;
}
pos = ra_lfsr_prev(ctx);
}
}
void ra_decide_gen(struct ra_context* ctx, ra_word_t* packet)
{
int index, bit;
ra_word_t word;
float data;
for (index = 0; index < ctx->ra_data_length; index++) {
word = 0;
for (bit = 0; bit < RA_BITCOUNT; bit++) {
data = ctx->ra_dataword_gen[index * RA_BITCOUNT + bit];
word |= (data < 0.0f) << bit;
}
packet[index] = word;
}
}
void ra_decoder_gen(struct ra_context* ctx,
float* softbits,
ra_word_t* packet,
int passes)
{
int count, seqno;
float* codeword;
ra_prepare_gen(ctx, softbits);
for (count = 0; count < passes; count++) {
codeword = ctx->ra_codeword_gen;
for (seqno = 0; seqno < 4; seqno++) {
ra_lfsr_init(ctx, seqno);
ra_improve_gen(ctx, codeword, seqno == 0 ? 1 : RA_PUNCTURE_RATE, count > 0);
codeword +=
(seqno == 0 ? ctx->ra_data_length : ctx->ra_chck_length) * RA_BITCOUNT;
}
assert(ctx->ra_codeword_gen + ctx->ra_code_length * RA_BITCOUNT == codeword);
}
ra_decide_gen(ctx, packet);
}
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