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/*---------------------------------------------------------------------------*\
FILE........: gp_interleaver.c
AUTHOR......: David Rowe
DATE CREATED: April 2018
Golden Prime Interleaver. My interpretation of "On the Analysis and
Design of Good Algebraic Interleavers", Xie et al,eq (5).
See also octave/gp_interleaver.m
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2018 David Rowe
All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License version 2.1, as
published by the Free Software Foundation. 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 Lesser General Public License
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "gp_interleaver.h"
#include <assert.h>
#include <stdio.h>
/*
Choose b for Golden Prime Interleaver. b is chosen to be the
closest integer, which is relatively prime to N, to the Golden
section of N.
Implemented with a LUT in C for convenience, Octave version
has a more complete implementation. If you find you need some more
numbers head back to the Octave choose_interleaver_b() function.
*/
static const int b_table[] = {
48, 31, /* datac14: HRA_56_56, 40 data bits used */
56, 37, /* 700E: HRA_56_56 */
106, 67, /* 2020B: (112,56) partial protection */
112, 71, /* 700D: HRA_112_112 */
128, 83, /* datac0: H_128_256_5 */
192, 127, /* datac13: H_256_512_4, 128 data bits used */
210, 131, /* 2020: HRAb_396_504 with 312 data bits used */
736, 457, /* datac4: H_1024_2048_4f, 448 data bits used */
1024, 641, /* datac3: H_1024_2048_4f */
1290, 797, /* datac2: H2064_516_sparse */
4096, 2531 /* datac1: H_4096_8192_3d */
};
int choose_interleaver_b(int Nbits) {
int i;
for (i = 0; i < sizeof(b_table) / sizeof(int); i += 2) {
if (b_table[i] == Nbits) {
return b_table[i + 1];
}
}
/* if we get to here it means a Nbits we don't have in our table so choke */
fprintf(stderr, "gp_interleaver: Nbits: %d, b not found!\n", Nbits);
assert(0);
return -1;
}
void gp_interleave_comp(COMP interleaved_frame[], COMP frame[], int Nbits) {
int b = choose_interleaver_b(Nbits);
int i, j;
for (i = 0; i < Nbits; i++) {
j = (b * i) % Nbits;
interleaved_frame[j] = frame[i];
}
}
void gp_deinterleave_comp(COMP frame[], COMP interleaved_frame[], int Nbits) {
int b = choose_interleaver_b(Nbits);
int i, j;
for (i = 0; i < Nbits; i++) {
j = (b * i) % Nbits;
frame[i] = interleaved_frame[j];
}
}
void gp_interleave_float(float interleaved_frame[], float frame[], int Nbits) {
int b = choose_interleaver_b(Nbits);
int i, j;
for (i = 0; i < Nbits; i++) {
j = (b * i) % Nbits;
interleaved_frame[j] = frame[i];
}
}
void gp_deinterleave_float(float frame[], float interleaved_frame[],
int Nbits) {
int b = choose_interleaver_b(Nbits);
int i, j;
for (i = 0; i < Nbits; i++) {
j = (b * i) % Nbits;
frame[i] = interleaved_frame[j];
}
}
// The above work on complex numbers (e.g. OFDM symbols), so the below work on
// groups of two bits at a time to remain compatible with the above.
void gp_interleave_bits(char interleaved_frame[], char frame[], int Nbits) {
char temp[Nbits];
int b = choose_interleaver_b(Nbits);
int i, j;
for (i = 0; i < Nbits; i++) {
j = (b * i) % Nbits;
temp[j] = ((frame[i * 2] & 1) << 1) | (frame[i * 2 + 1] & 1);
}
for (i = 0; i < Nbits; i++) {
interleaved_frame[i * 2] = temp[i] >> 1;
interleaved_frame[i * 2 + 1] = temp[i] & 1;
}
}
void gp_deinterleave_bits(char frame[], char interleaved_frame[], int Nbits) {
char temp[Nbits];
int b = choose_interleaver_b(Nbits);
int i, j;
for (i = 0; i < Nbits; i++) {
j = (b * i) % Nbits;
temp[i] = ((interleaved_frame[j * 2] & 1) << 1) |
(interleaved_frame[j * 2 + 1] & 1);
}
for (i = 0; i < Nbits; i++) {
frame[i * 2] = temp[i] >> 1;
frame[i * 2 + 1] = temp[i] & 1;
}
}
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