mirror of https://github.com/wb2osz/direwolf.git
84 lines
2.6 KiB
C
84 lines
2.6 KiB
C
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//
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// This file is part of Dire Wolf, an amateur radio packet TNC.
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//
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// Copyright (C) 2019 John Langner, WB2OSZ
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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 2 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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// -----------------------------------------------------------------------
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//
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//
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// Most of this is based on:
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//
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// FX.25 Encoder
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// Author: Jim McGuire KB3MPL
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// Date: 23 October 2007
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//
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// This program is a single-file implementation of the FX.25 encapsulation
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// structure for use with AX.25 data packets. Details of the FX.25
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// specification are available at:
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// http://www.stensat.org/Docs/Docs.htm
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//
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// This program implements a single RS(255,239) FEC structure. Future
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// releases will incorporate more capabilities as accommodated in the FX.25
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// spec.
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//
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// The Reed Solomon encoding routines are based on work performed by
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// Phil Karn. Phil was kind enough to release his code under the GPL, as
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// noted below. Consequently, this FX.25 implementation is also released
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// under the terms of the GPL.
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//
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// Phil Karn's original copyright notice:
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/* Test the Reed-Solomon codecs
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* for various block sizes and with random data and random error patterns
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*
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* Copyright 2002 Phil Karn, KA9Q
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* May be used under the terms of the GNU General Public License (GPL)
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*
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <ctype.h>
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#include "fx25.h"
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void ENCODE_RS(struct rs * restrict rs, DTYPE * restrict data, DTYPE * restrict bb)
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{
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int i, j;
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DTYPE feedback;
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memset(bb,0,NROOTS*sizeof(DTYPE)); // clear out the FEC data area
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for(i=0;i<NN-NROOTS;i++){
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feedback = INDEX_OF[data[i] ^ bb[0]];
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if(feedback != A0){ /* feedback term is non-zero */
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for(j=1;j<NROOTS;j++)
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bb[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS-j])];
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}
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/* Shift */
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memmove(&bb[0],&bb[1],sizeof(DTYPE)*(NROOTS-1));
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if(feedback != A0)
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bb[NROOTS-1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])];
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else
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bb[NROOTS-1] = 0;
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}
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}
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// end fx25_encode.c
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