GCR encoding/decoding
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adamdunkels
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163
core/lib/gcr.c
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163
core/lib/gcr.c
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/*
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* Copyright (c) 2006, Swedish Institute of Computer Science
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This file is part of the Contiki operating system.
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*
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* @(#)$Id: gcr.c,v 1.1 2006/10/05 09:23:41 adamdunkels Exp $
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*/
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/**
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* \file
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* Implementation of GCR coding/decoding
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* \author
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* Joakim Eriksson <joakime@sics.se>
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*
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*/
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/* GCR conversion table - used for converting ordinary byte to 10-bits */
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/* (or 4 bits to 5) */
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static const unsigned char GCR_encode[16] = {
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0x0a, 0x0b, 0x12, 0x13,
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0x0e, 0x0f, 0x16, 0x17,
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0x09, 0x19, 0x1a, 0x1b,
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0x0d, 0x1d, 0x1e, 0x15
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};
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/* 5 bits > 4 bits (0xff => invalid) */
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static const unsigned char GCR_decode[32] = {
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0xff, 0xff, 0xff, 0xff, // 0 - 3invalid...
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0xff, 0xff, 0xff, 0xff, // 4 - 7 invalid...
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0xff, 0x08, 0x00, 0x01, // 8 invalid... 9 = 8, a = 0, b = 1
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0xff, 0x0c, 0x04, 0x05, // c invalid... d = c, e = 4, f = 5
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0xff, 0xff, 0x02, 0x03, // 10-11 invalid...
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0xff, 0x0f, 0x06, 0x07, // 14 invalid...
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0xff, 0x09, 0x0a, 0x0b, // 18 invalid...
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0xff, 0x0d, 0x0e, 0xff, // 1c, 1f invalid...
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};
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static unsigned char gcr_bits = 0;
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static unsigned short gcr_val = 0;
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/* Call before starting encoding or decoding */
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void gcr_init() {
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gcr_val = 0;
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gcr_bits = 0;
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}
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/* Use this to check if encoding / decoding is complete for now */
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unsigned char gcr_finished() {
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return gcr_bits == 0;
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}
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/* Encode one character - and store in bits - get encoded with get_encoded */
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void gcr_encode(unsigned char raw_data) {
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gcr_val |=
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((GCR_encode[raw_data >> 4u] << 5u ) |
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GCR_encode[raw_data & 0xf]) << gcr_bits;
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gcr_bits += 10;
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}
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/* Gets the current char of the encoded stream */
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unsigned char gcr_get_encoded(unsigned char *raw_data) {
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if (gcr_bits >= 8) {
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*raw_data = (unsigned char) (gcr_val & 0xff);
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gcr_val = gcr_val >> 8u;
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gcr_bits = gcr_bits - 8;
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return 1;
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}
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return 0;
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}
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/* Decode one char - result can be get from get_decoded */
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void gcr_decode(unsigned char gcr_data) {
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gcr_val |= gcr_data << gcr_bits;
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gcr_bits += 8;
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}
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/* check if the current decoded stream is correct */
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unsigned char gcr_valid() {
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if (gcr_bits >= 10) {
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unsigned short val = gcr_val & 0x3ff;
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if ((GCR_decode[val >> 5u] << 4u) == 0xff ||
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(GCR_decode[val & 0x1f]) == 0xff) {
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return 0;
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}
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}
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return 1;
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}
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/* gets the decoded stream - if any char is available */
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unsigned char gcr_get_decoded(unsigned char *raw_data) {
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if (gcr_bits >= 10) {
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unsigned short val = gcr_val & 0x3ff;
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*raw_data = (unsigned char) ((GCR_decode[val >> 5] << 4) |
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(GCR_decode[val & 0x1f]));
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gcr_val = gcr_val >> 10;
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gcr_bits = gcr_bits - 10;
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return 1;
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}
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return 0;
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}
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/*
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static const char encoded[] = {
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0x4a, 0x25, 0xa5, 0xfc, 0x96, 0xff, 0xff, 0xb5, 0xd4, 0x5a, 0xea, 0xff, 0xff, 0xaa, 0xd3, 0xff
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};
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int main(int argc, char **argv) {
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// unsigned char c[] = "testing gcr 1 2 3 4 5 6...";
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unsigned char c[] = { 0, 8, 0xe0, 0x2b, 0xac, 0x10, 0x01, 0x11, 0x50, 0xff, 0xf4, 0xa4, 0x00 };
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unsigned char c2[200];
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int pos = 0, pos2 = 0, i = 0;
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printf("Testing GCR on: %s \n", c);
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gcr_init();
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for (i = 0; i < sizeof(c); i++) {
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gcr_encode(c[i]);
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while(gcr_get_encoded(&c2[pos])) {
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printf("%02x=>%02x ", c[i], c2[pos]);
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pos++;
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}
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}
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printf("\n");
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printf("Encoded result %d chars (from %d) \n", pos, i);
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gcr_init();
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for (i = 0; i < pos; i++) {
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gcr_decode(c2[i]);
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if(!gcr_valid()) {
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printf("GCR: not valid\n");
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}
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while(gcr_get_decoded(&c[pos2])) {
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pos2++;
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}
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}
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printf("GCR: %s\n",c);
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}
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*/
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52
core/lib/gcr.h
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52
core/lib/gcr.h
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@ -0,0 +1,52 @@
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/*
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* Copyright (c) 2006, Swedish Institute of Computer Science.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $Id: gcr.h,v 1.1 2006/10/05 09:23:41 adamdunkels Exp $
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*
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* -----------------------------------------------------------------
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*
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* Author : Adam Dunkels, Joakim Eriksson, Niclas Finne
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* Created : 2006-10-02
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* Updated : $Date: 2006/10/05 09:23:41 $
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* $Revision: 1.1 $
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*/
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#ifndef __GCR_H__
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#define __GCR_H__
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void gcr_init();
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unsigned char gcr_finished();
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void gcr_encode(unsigned char raw_data);
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void gcr_decode(unsigned char gcr_data);
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unsigned char gcr_get_encoded(unsigned char *raw_data);
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unsigned char gcr_get_decoded(unsigned char *raw_data);
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unsigned char gcr_valid();
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#endif /* __GCR_H__ */
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