Bastian Bloessl
437 lines
15 KiB
C++
437 lines
15 KiB
C++
/*
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* Copyright 1995 Phil Karn, KA9Q
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* Copyright 2008 Free Software Foundation, Inc.
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* 2014 Added SSE2 implementation Bogdan Diaconescu
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*
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* This file is part of GNU Radio
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*
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* GNU Radio is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* GNU Radio is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU Radio; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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/*
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* Viterbi decoder for K=7 rate=1/2 convolutional code
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* Some modifications from original Karn code by Matt Ettus
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* Major modifications by adding SSE2 code by Bogdan Diaconescu
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*/
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#include "viterbi_decoder_generic.h"
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#include <cstring>
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#include <iostream>
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/* The basic Viterbi decoder operation, called a "butterfly"
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* operation because of the way it looks on a trellis diagram. Each
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* butterfly involves an Add-Compare-Select (ACS) operation on the two nodes
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* where the 0 and 1 paths from the current node merge at the next step of
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* the trellis.
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*
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* The code polynomials are assumed to have 1's on both ends. Given a
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* function encode_state() that returns the two symbols for a given
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* encoder state in the low two bits, such a code will have the following
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* identities for even 'n' < 64:
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*
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* encode_state(n) = encode_state(n+65)
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* encode_state(n+1) = encode_state(n+64) = (3 ^ encode_state(n))
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*
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* Any convolutional code you would actually want to use will have
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* these properties, so these assumptions aren't too limiting.
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*
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* Doing this as a macro lets the compiler evaluate at compile time the
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* many expressions that depend on the loop index and encoder state and
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* emit them as immediate arguments.
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* This makes an enormous difference on register-starved machines such
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* as the Intel x86 family where evaluating these expressions at runtime
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* would spill over into memory.
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*/
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#define BUTTERFLY(i, sym) \
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{ \
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int m0, m1, m2, m3; \
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/* ACS for 0 branch */ \
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m0 = state[i].metric + mets[sym]; /* 2*i */ \
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m1 = state[i + 32].metric + mets[3 ^ sym]; /* 2*i + 64 */ \
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if (m0 > m1) { \
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next[2 * i].metric = m0; \
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next[2 * i].path = state[i].path << 1; \
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} else { \
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next[2 * i].metric = m1; \
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next[2 * i].path = (state[i + 32].path << 1) | 1; \
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} \
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/* ACS for 1 branch */ \
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m2 = state[i].metric + mets[3 ^ sym]; /* 2*i + 1 */ \
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m3 = state[i + 32].metric + mets[sym]; /* 2*i + 65 */ \
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if (m2 > m3) { \
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next[2 * i + 1].metric = m2; \
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next[2 * i + 1].path = state[i].path << 1; \
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} else { \
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next[2 * i + 1].metric = m3; \
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next[2 * i + 1].path = (state[i + 32].path << 1) | 1; \
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} \
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}
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using namespace gr::ieee802_11;
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void viterbi_decoder::viterbi_butterfly2_generic(unsigned char* symbols,
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unsigned char* mm0,
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unsigned char* mm1,
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unsigned char* pp0,
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unsigned char* pp1)
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{
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int i, j, k;
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unsigned char *metric0, *metric1;
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unsigned char *path0, *path1;
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metric0 = mm0;
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path0 = pp0;
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metric1 = mm1;
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path1 = pp1;
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// Operate on 4 symbols (2 bits) at a time
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unsigned char m0[16], m1[16], m2[16], m3[16], decision0[16], decision1[16],
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survivor0[16], survivor1[16];
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unsigned char metsv[16], metsvm[16];
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unsigned char shift0[16], shift1[16];
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unsigned char tmp0[16], tmp1[16];
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unsigned char sym0v[16], sym1v[16];
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unsigned short simd_epi16;
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for (j = 0; j < 16; j++) {
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sym0v[j] = symbols[0];
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sym1v[j] = symbols[1];
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}
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for (i = 0; i < 2; i++) {
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if (symbols[0] == 2) {
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for (j = 0; j < 16; j++) {
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metsvm[j] = d_branchtab27_generic[1].c[(i * 16) + j] ^ sym1v[j];
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metsv[j] = 1 - metsvm[j];
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}
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} else if (symbols[1] == 2) {
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for (j = 0; j < 16; j++) {
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metsvm[j] = d_branchtab27_generic[0].c[(i * 16) + j] ^ sym0v[j];
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metsv[j] = 1 - metsvm[j];
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}
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} else {
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for (j = 0; j < 16; j++) {
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metsvm[j] = (d_branchtab27_generic[0].c[(i * 16) + j] ^ sym0v[j]) +
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(d_branchtab27_generic[1].c[(i * 16) + j] ^ sym1v[j]);
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metsv[j] = 2 - metsvm[j];
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}
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}
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for (j = 0; j < 16; j++) {
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m0[j] = metric0[(i * 16) + j] + metsv[j];
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m1[j] = metric0[((i + 2) * 16) + j] + metsvm[j];
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m2[j] = metric0[(i * 16) + j] + metsvm[j];
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m3[j] = metric0[((i + 2) * 16) + j] + metsv[j];
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}
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for (j = 0; j < 16; j++) {
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decision0[j] = ((m0[j] - m1[j]) > 0) ? 0xff : 0x0;
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decision1[j] = ((m2[j] - m3[j]) > 0) ? 0xff : 0x0;
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survivor0[j] = (decision0[j] & m0[j]) | ((~decision0[j]) & m1[j]);
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survivor1[j] = (decision1[j] & m2[j]) | ((~decision1[j]) & m3[j]);
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}
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for (j = 0; j < 16; j += 2) {
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simd_epi16 = path0[(i * 16) + j];
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simd_epi16 |= path0[(i * 16) + (j + 1)] << 8;
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simd_epi16 <<= 1;
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shift0[j] = simd_epi16;
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shift0[j + 1] = simd_epi16 >> 8;
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simd_epi16 = path0[((i + 2) * 16) + j];
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simd_epi16 |= path0[((i + 2) * 16) + (j + 1)] << 8;
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simd_epi16 <<= 1;
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shift1[j] = simd_epi16;
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shift1[j + 1] = simd_epi16 >> 8;
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}
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for (j = 0; j < 16; j++) {
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shift1[j] = shift1[j] + 1;
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}
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for (j = 0, k = 0; j < 16; j += 2, k++) {
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metric1[(2 * i * 16) + j] = survivor0[k];
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metric1[(2 * i * 16) + (j + 1)] = survivor1[k];
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}
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for (j = 0; j < 16; j++) {
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tmp0[j] = (decision0[j] & shift0[j]) | ((~decision0[j]) & shift1[j]);
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}
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for (j = 0, k = 8; j < 16; j += 2, k++) {
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metric1[((2 * i + 1) * 16) + j] = survivor0[k];
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metric1[((2 * i + 1) * 16) + (j + 1)] = survivor1[k];
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}
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for (j = 0; j < 16; j++) {
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tmp1[j] = (decision1[j] & shift0[j]) | ((~decision1[j]) & shift1[j]);
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}
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for (j = 0, k = 0; j < 16; j += 2, k++) {
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path1[(2 * i * 16) + j] = tmp0[k];
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path1[(2 * i * 16) + (j + 1)] = tmp1[k];
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}
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for (j = 0, k = 8; j < 16; j += 2, k++) {
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path1[((2 * i + 1) * 16) + j] = tmp0[k];
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path1[((2 * i + 1) * 16) + (j + 1)] = tmp1[k];
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}
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}
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metric0 = mm1;
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path0 = pp1;
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metric1 = mm0;
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path1 = pp0;
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for (j = 0; j < 16; j++) {
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sym0v[j] = symbols[2];
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sym1v[j] = symbols[3];
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}
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for (i = 0; i < 2; i++) {
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if (symbols[2] == 2) {
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for (j = 0; j < 16; j++) {
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metsvm[j] = d_branchtab27_generic[1].c[(i * 16) + j] ^ sym1v[j];
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metsv[j] = 1 - metsvm[j];
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}
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} else if (symbols[3] == 2) {
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for (j = 0; j < 16; j++) {
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metsvm[j] = d_branchtab27_generic[0].c[(i * 16) + j] ^ sym0v[j];
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metsv[j] = 1 - metsvm[j];
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}
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} else {
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for (j = 0; j < 16; j++) {
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metsvm[j] = (d_branchtab27_generic[0].c[(i * 16) + j] ^ sym0v[j]) +
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(d_branchtab27_generic[1].c[(i * 16) + j] ^ sym1v[j]);
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metsv[j] = 2 - metsvm[j];
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}
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}
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for (j = 0; j < 16; j++) {
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m0[j] = metric0[(i * 16) + j] + metsv[j];
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m1[j] = metric0[((i + 2) * 16) + j] + metsvm[j];
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m2[j] = metric0[(i * 16) + j] + metsvm[j];
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m3[j] = metric0[((i + 2) * 16) + j] + metsv[j];
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}
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for (j = 0; j < 16; j++) {
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decision0[j] = ((m0[j] - m1[j]) > 0) ? 0xff : 0x0;
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decision1[j] = ((m2[j] - m3[j]) > 0) ? 0xff : 0x0;
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survivor0[j] = (decision0[j] & m0[j]) | ((~decision0[j]) & m1[j]);
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survivor1[j] = (decision1[j] & m2[j]) | ((~decision1[j]) & m3[j]);
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}
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for (j = 0; j < 16; j += 2) {
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simd_epi16 = path0[(i * 16) + j];
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simd_epi16 |= path0[(i * 16) + (j + 1)] << 8;
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simd_epi16 <<= 1;
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shift0[j] = simd_epi16;
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shift0[j + 1] = simd_epi16 >> 8;
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simd_epi16 = path0[((i + 2) * 16) + j];
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simd_epi16 |= path0[((i + 2) * 16) + (j + 1)] << 8;
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simd_epi16 <<= 1;
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shift1[j] = simd_epi16;
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shift1[j + 1] = simd_epi16 >> 8;
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}
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for (j = 0; j < 16; j++) {
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shift1[j] = shift1[j] + 1;
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}
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for (j = 0, k = 0; j < 16; j += 2, k++) {
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metric1[(2 * i * 16) + j] = survivor0[k];
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metric1[(2 * i * 16) + (j + 1)] = survivor1[k];
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}
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for (j = 0; j < 16; j++) {
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tmp0[j] = (decision0[j] & shift0[j]) | ((~decision0[j]) & shift1[j]);
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}
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for (j = 0, k = 8; j < 16; j += 2, k++) {
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metric1[((2 * i + 1) * 16) + j] = survivor0[k];
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metric1[((2 * i + 1) * 16) + (j + 1)] = survivor1[k];
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}
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for (j = 0; j < 16; j++) {
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tmp1[j] = (decision1[j] & shift0[j]) | ((~decision1[j]) & shift1[j]);
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}
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for (j = 0, k = 0; j < 16; j += 2, k++) {
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path1[(2 * i * 16) + j] = tmp0[k];
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path1[(2 * i * 16) + (j + 1)] = tmp1[k];
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}
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for (j = 0, k = 8; j < 16; j += 2, k++) {
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path1[((2 * i + 1) * 16) + j] = tmp0[k];
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path1[((2 * i + 1) * 16) + (j + 1)] = tmp1[k];
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}
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}
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}
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// Find current best path
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unsigned char viterbi_decoder::viterbi_get_output_generic(unsigned char* mm0,
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unsigned char* pp0,
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int ntraceback,
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unsigned char* outbuf)
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{
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int i;
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int bestmetric, minmetric;
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int beststate = 0;
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int pos = 0;
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int j;
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// circular buffer with the last ntraceback paths
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d_store_pos = (d_store_pos + 1) % ntraceback;
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for (i = 0; i < 4; i++) {
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for (j = 0; j < 16; j++) {
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d_mmresult[(i * 16) + j] = mm0[(i * 16) + j];
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d_ppresult[d_store_pos][(i * 16) + j] = pp0[(i * 16) + j];
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}
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}
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// Find out the best final state
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bestmetric = d_mmresult[beststate];
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minmetric = d_mmresult[beststate];
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for (i = 1; i < 64; i++) {
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if (d_mmresult[i] > bestmetric) {
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bestmetric = d_mmresult[i];
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beststate = i;
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}
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if (d_mmresult[i] < minmetric) {
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minmetric = d_mmresult[i];
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}
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}
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// Trace back
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for (i = 0, pos = d_store_pos; i < (ntraceback - 1); i++) {
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// Obtain the state from the output bits
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// by clocking in the output bits in reverse order.
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// The state has only 6 bits
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beststate = d_ppresult[pos][beststate] >> 2;
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pos = (pos - 1 + ntraceback) % ntraceback;
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}
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// Store output byte
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*outbuf = d_ppresult[pos][beststate];
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for (i = 0; i < 4; i++) {
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for (j = 0; j < 16; j++) {
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pp0[(i * 16) + j] = 0;
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mm0[(i * 16) + j] = mm0[(i * 16) + j] - minmetric;
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}
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}
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return bestmetric;
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}
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uint8_t* viterbi_decoder::decode(ofdm_param* ofdm, frame_param* frame, uint8_t* in)
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{
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d_ofdm = ofdm;
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d_frame = frame;
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reset();
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uint8_t* depunctured = depuncture(in);
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int in_count = 0;
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int out_count = 0;
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int n_decoded = 0;
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while (n_decoded < d_frame->n_data_bits) {
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if ((in_count % 4) == 0) { // 0 or 3
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viterbi_butterfly2_generic(&depunctured[in_count & 0xfffffffc],
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d_metric0_generic,
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d_metric1_generic,
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d_path0_generic,
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d_path1_generic);
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if ((in_count > 0) && (in_count % 16) == 8) { // 8 or 11
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unsigned char c;
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viterbi_get_output_generic(
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d_metric0_generic, d_path0_generic, d_ntraceback, &c);
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if (out_count >= d_ntraceback) {
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for (int i = 0; i < 8; i++) {
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d_decoded[(out_count - d_ntraceback) * 8 + i] =
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(c >> (7 - i)) & 0x1;
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n_decoded++;
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}
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}
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out_count++;
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}
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}
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in_count++;
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}
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return d_decoded;
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}
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void viterbi_decoder::reset()
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{
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viterbi_chunks_init_generic();
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switch (d_ofdm->encoding) {
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case BPSK_1_2:
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case QPSK_1_2:
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case QAM16_1_2:
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d_ntraceback = 5;
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d_depuncture_pattern = PUNCTURE_1_2;
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d_k = 1;
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break;
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case QAM64_2_3:
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d_ntraceback = 9;
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d_depuncture_pattern = PUNCTURE_2_3;
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d_k = 2;
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break;
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case BPSK_3_4:
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case QPSK_3_4:
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case QAM16_3_4:
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case QAM64_3_4:
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d_ntraceback = 10;
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d_depuncture_pattern = PUNCTURE_3_4;
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d_k = 3;
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break;
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}
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}
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// Initialize starting metrics to prefer 0 state
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void viterbi_decoder::viterbi_chunks_init_generic()
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{
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int i, j;
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for (i = 0; i < 4; i++) {
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d_metric0_generic[i] = 0;
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d_path0_generic[i] = 0;
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}
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int polys[2] = { 0x6d, 0x4f };
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for (i = 0; i < 32; i++) {
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d_branchtab27_generic[0].c[i] =
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(polys[0] < 0) ^ PARTAB[(2 * i) & abs(polys[0])] ? 1 : 0;
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d_branchtab27_generic[1].c[i] =
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(polys[1] < 0) ^ PARTAB[(2 * i) & abs(polys[1])] ? 1 : 0;
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}
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for (i = 0; i < 64; i++) {
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d_mmresult[i] = 0;
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for (j = 0; j < TRACEBACK_MAX; j++) {
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d_ppresult[j][i] = 0;
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}
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}
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}
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