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123 lines
2.9 KiB
C++
123 lines
2.9 KiB
C++
/*---------------------------------------------------------------------------*\
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FILE........: gp_interleaver.c
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AUTHOR......: David Rowe
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DATE CREATED: April 2018
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Golden Prime Interleaver. My interpretation of "On the Analysis and
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Design of Good Algebraic Interleavers", Xie et al,eq (5).
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See also octvae/gp_interleaver.m
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\*---------------------------------------------------------------------------*/
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/*
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Copyright (C) 2018 David Rowe
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All rights reserved.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License version 2.1, as
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published by the Free Software Foundation. This program is
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distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <assert.h>
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#include <stdio.h>
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#include "gp_interleaver.h"
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namespace FreeDV
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{
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/*
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Choose b for Golden Prime Interleaver. b is chosen to be the
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closest integer, which is relatively prime to N, to the Golden
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section of N.
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Implemented with a LUT in C for convenience, Octave version
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has a more complete implementation.
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*/
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int b_table[] = {
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112,71,
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224,139,
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448,277,
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672,419,
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896,557,
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1120,701,
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1344,839,
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1568,971,
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1792,1109,
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2016,1249,
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2240,1399,
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2464,1523,
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2688,1663,
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2912,1801,
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3136,1949,
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3360,2081,
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3584,2213
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};
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int choose_interleaver_b(int Nbits)
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{
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unsigned int i;
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for(i=0; i<sizeof(b_table)/(2*sizeof(int)); i+=2) {
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if (b_table[i] == Nbits) {
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return b_table[i+1];
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}
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}
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/* if we get it means a Nbits we dont have in our table so choke */
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fprintf(stderr, "FreeDV::choose_interleaver_b: Nbits not in table return 0 as default");
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return 0;
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}
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void gp_interleave_comp(COMP interleaved_frame[], COMP frame[], int Nbits) {
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int b = choose_interleaver_b(Nbits);
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int i,j;
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for (i=0; i<Nbits; i++) {
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j = (b*i) % Nbits;
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interleaved_frame[j] = frame[i];
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}
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}
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void gp_deinterleave_comp(COMP frame[], COMP interleaved_frame[], int Nbits) {
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int b = choose_interleaver_b(Nbits);
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int i,j;
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for (i=0; i<Nbits; i++) {
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j = (b*i) % Nbits;
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frame[i] = interleaved_frame[j];
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}
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}
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void gp_interleave_float(float interleaved_frame[], float frame[], int Nbits) {
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int b = choose_interleaver_b(Nbits);
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int i,j;
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for (i=0; i<Nbits; i++) {
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j = (b*i) % Nbits;
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interleaved_frame[j] = frame[i];
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}
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}
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void gp_deinterleave_float(float frame[], float interleaved_frame[], int Nbits) {
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int b = choose_interleaver_b(Nbits);
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int i,j;
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for (i=0; i<Nbits; i++) {
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j = (b*i) % Nbits;
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frame[i] = interleaved_frame[j];
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}
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}
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} // FreeDV
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