110 lines
2.8 KiB
C++
110 lines
2.8 KiB
C++
/* -*- c++ -*- */
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/*
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* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
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*
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* Copyright (C) 2016, Libre Space Foundation <http://librespacefoundation.org/>
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*
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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 General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <gnuradio/io_signature.h>
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#include <satnogs/whitening.h>
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#include <satnogs/utils.h>
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namespace gr {
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namespace satnogs {
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/**
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* Data whitening and de-whitening class
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* @param mask the polynomial mask
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* @param seed the initial seed
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* @param order the order of the shift register. This is equal to the
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* number of memory stages.
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*/
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whitening::whitening (uint32_t mask, uint32_t seed, uint32_t order) :
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d_lut_len (std::pow (2, order)),
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d_lut_idx (0)
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{
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size_t i;
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size_t j;
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uint32_t cnt;
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uint32_t shift_reg = seed;
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if (order > 32) {
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throw std::invalid_argument ("The maximum allowed order is 32");
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}
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d_lut = new uint8_t[d_lut_len];
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for (i = 0; i < d_lut_len; i++) {
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d_lut[i] = shift_reg & 0xFF;
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for (j = 0; j < 8; j++) {
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cnt = bit_count (shift_reg & mask) % 2;
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shift_reg = shift_reg >> 1;
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shift_reg |= cnt << (order - 1);
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}
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}
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}
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whitening::~whitening()
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{
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delete [] d_lut;
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}
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/**
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* Resets the scrambler (or the descrambler) to the initial stage and
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* the initial seed.
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*/
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void
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whitening::reset ()
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{
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d_lut_idx = 0;
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}
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/**
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* Performs data scrambling
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* @param out the output buffer
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* @param in the input buffer
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* @param len the number of the bytes to be scrambled
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*/
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void
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whitening::scramble (uint8_t* out, const uint8_t* in, size_t len)
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{
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size_t i;
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for(i = 0; i < len; i++){
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out[i] = in[i] ^ d_lut[ (d_lut_idx + i ) % d_lut_len];
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}
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d_lut_idx = (d_lut_idx + len ) % d_lut_len;
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}
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/**
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* Performs data de-scrambling
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* @param out the output buffer
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* @param in the input buffer
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* @param len the number of the bytes to be de-scrambled
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*/
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void
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whitening::descramble (uint8_t* out, const uint8_t* in, size_t len)
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{
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scramble(out, in, len);
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}
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} /* namespace satnogs */
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} /* namespace gr */
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