375 lines
8.8 KiB
C++
375 lines
8.8 KiB
C++
/*
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* Copyright (C) 2016 by Jonathan Naylor, G4KLX
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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; version 2 of the License.
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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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#include "DMRTrellis.h"
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#include "DMRDefines.h"
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#include "Log.h"
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#include <cstdio>
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#include <cassert>
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const unsigned int INTERLEAVE_TABLE[] = {
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0U, 1U, 8U, 9U, 16U, 17U, 24U, 25U, 32U, 33U, 40U, 41U, 48U, 49U, 56U, 57U, 64U, 65U, 72U, 73U, 80U, 81U, 88U, 89U, 96U, 97U,
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2U, 3U, 10U, 11U, 18U, 19U, 26U, 27U, 34U, 35U, 42U, 43U, 50U, 51U, 58U, 59U, 66U, 67U, 74U, 75U, 82U, 83U, 90U, 91U,
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4U, 5U, 12U, 13U, 20U, 21U, 28U, 29U, 36U, 37U, 44U, 45U, 52U, 53U, 60U, 61U, 68U, 69U, 76U, 77U, 84U, 85U, 92U, 93U,
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6U, 7U, 14U, 15U, 22U, 23U, 30U, 31U, 38U, 39U, 46U, 47U, 54U, 55U, 62U, 63U, 70U, 71U, 78U, 79U, 86U, 87U, 94U, 95U};
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const unsigned char ENCODE_TABLE[] = {
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0U, 8U, 4U, 12U, 2U, 10U, 6U, 14U,
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4U, 12U, 2U, 10U, 6U, 14U, 0U, 8U,
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1U, 9U, 5U, 13U, 3U, 11U, 7U, 15U,
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5U, 13U, 3U, 11U, 7U, 15U, 1U, 9U,
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3U, 11U, 7U, 15U, 1U, 9U, 5U, 13U,
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7U, 15U, 1U, 9U, 5U, 13U, 3U, 11U,
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2U, 10U, 6U, 14U, 0U, 8U, 4U, 12U,
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6U, 14U, 0U, 8U, 4U, 12U, 2U, 10U};
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const unsigned char BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U};
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#define WRITE_BIT(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
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#define READ_BIT(p,i) (p[(i)>>3] & BIT_MASK_TABLE[(i)&7])
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CDMRTrellis::CDMRTrellis()
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{
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}
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CDMRTrellis::~CDMRTrellis()
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{
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}
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bool CDMRTrellis::decode(const unsigned char* data, unsigned char* payload)
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{
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assert(data != NULL);
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assert(payload != NULL);
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signed char dibits[98U];
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deinterleave(data, dibits);
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unsigned char points[49U];
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dibitsToPoints(dibits, points);
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// Check the original code
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unsigned char tribits[49U];
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unsigned int failPos = checkCode(points, tribits);
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if (failPos == 999U) {
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tribitsToBits(tribits, payload);
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return true;
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}
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unsigned char savePoints[49U];
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for (unsigned int i = 0U; i < 49U; i++)
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savePoints[i] = points[i];
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bool ret = fixCode(points, failPos, payload);
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if (ret)
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return true;
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if (failPos == 0U)
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return false;
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// Backtrack one place for a last go
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return fixCode(savePoints, failPos - 1U, payload);
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}
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void CDMRTrellis::encode(const unsigned char* payload, unsigned char* data)
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{
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assert(payload != NULL);
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assert(data != NULL);
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unsigned char tribits[49U];
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bitsToTribits(payload, tribits);
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unsigned char points[49U];
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unsigned char state = 0U;
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for (unsigned int i = 0U; i < 49U; i++) {
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unsigned char tribit = tribits[i];
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points[i] = ENCODE_TABLE[state * 8U + tribit];
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state = tribit;
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}
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signed char dibits[98U];
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pointsToDibits(points, dibits);
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interleave(dibits, data);
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}
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void CDMRTrellis::deinterleave(const unsigned char* data, signed char* dibits) const
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{
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for (unsigned int i = 0U; i < 98U; i++) {
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unsigned int n = i * 2U + 0U;
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if (n >= 98U) n += 68U;
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bool b1 = READ_BIT(data, n) != 0x00U;
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n = i * 2U + 1U;
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if (n >= 98U) n += 68U;
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bool b2 = READ_BIT(data, n) != 0x00U;
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signed char dibit;
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if (!b1 && b2)
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dibit = +3;
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else if (!b1 && !b2)
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dibit = +1;
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else if (b1 && !b2)
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dibit = -1;
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else
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dibit = -3;
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n = INTERLEAVE_TABLE[i];
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dibits[n] = dibit;
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}
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}
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void CDMRTrellis::interleave(const signed char* dibits, unsigned char* data) const
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{
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for (unsigned int i = 0U; i < 98U; i++) {
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unsigned int n = INTERLEAVE_TABLE[i];
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bool b1, b2;
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switch (dibits[n]) {
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case +3:
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b1 = false;
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b2 = true;
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break;
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case +1:
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b1 = false;
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b2 = false;
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break;
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case -1:
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b1 = true;
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b2 = false;
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break;
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default:
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b1 = true;
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b2 = true;
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break;
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}
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n = i * 2U + 0U;
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if (n >= 98U) n += 68U;
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WRITE_BIT(data, n, b1);
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n = i * 2U + 1U;
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if (n >= 98U) n += 68U;
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WRITE_BIT(data, n, b2);
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}
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}
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void CDMRTrellis::dibitsToPoints(const signed char* dibits, unsigned char* points) const
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{
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for (unsigned int i = 0U; i < 49U; i++) {
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if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == -1)
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points[i] = 0U;
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else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == -1)
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points[i] = 1U;
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else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == -3)
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points[i] = 2U;
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else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == -3)
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points[i] = 3U;
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else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == -1)
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points[i] = 4U;
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else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == -1)
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points[i] = 5U;
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else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == -3)
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points[i] = 6U;
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else if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == -3)
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points[i] = 7U;
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else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == +3)
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points[i] = 8U;
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else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == +3)
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points[i] = 9U;
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else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == +1)
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points[i] = 10U;
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else if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == +1)
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points[i] = 11U;
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else if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == +3)
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points[i] = 12U;
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else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == +3)
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points[i] = 13U;
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else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == +1)
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points[i] = 14U;
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else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == +1)
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points[i] = 15U;
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}
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}
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void CDMRTrellis::pointsToDibits(const unsigned char* points, signed char* dibits) const
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{
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for (unsigned int i = 0U; i < 49U; i++) {
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switch (points[i]) {
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case 0U:
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dibits[i * 2U + 0U] = +1;
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dibits[i * 2U + 1U] = -1;
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break;
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case 1U:
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dibits[i * 2U + 0U] = -1;
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dibits[i * 2U + 1U] = -1;
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break;
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case 2U:
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dibits[i * 2U + 0U] = +3;
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dibits[i * 2U + 1U] = -3;
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break;
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case 3U:
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dibits[i * 2U + 0U] = -3;
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dibits[i * 2U + 1U] = -3;
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break;
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case 4U:
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dibits[i * 2U + 0U] = -3;
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dibits[i * 2U + 1U] = -1;
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break;
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case 5U:
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dibits[i * 2U + 0U] = +3;
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dibits[i * 2U + 1U] = -1;
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break;
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case 6U:
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dibits[i * 2U + 0U] = -1;
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dibits[i * 2U + 1U] = -3;
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break;
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case 7U:
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dibits[i * 2U + 0U] = +1;
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dibits[i * 2U + 1U] = -3;
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break;
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case 8U:
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dibits[i * 2U + 0U] = -3;
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dibits[i * 2U + 1U] = +3;
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break;
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case 9U:
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dibits[i * 2U + 0U] = +3;
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dibits[i * 2U + 1U] = +3;
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break;
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case 10U:
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dibits[i * 2U + 0U] = -1;
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dibits[i * 2U + 1U] = +1;
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break;
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case 11U:
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dibits[i * 2U + 0U] = +1;
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dibits[i * 2U + 1U] = +1;
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break;
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case 12U:
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dibits[i * 2U + 0U] = +1;
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dibits[i * 2U + 1U] = +3;
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break;
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case 13U:
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dibits[i * 2U + 0U] = -1;
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dibits[i * 2U + 1U] = +3;
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break;
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case 14U:
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dibits[i * 2U + 0U] = +3;
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dibits[i * 2U + 1U] = +1;
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break;
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default:
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dibits[i * 2U + 0U] = -3;
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dibits[i * 2U + 1U] = +1;
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break;
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}
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}
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}
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void CDMRTrellis::bitsToTribits(const unsigned char* payload, unsigned char* tribits) const
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{
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for (unsigned int i = 0U; i < 48U; i++) {
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unsigned int n = 143U - i * 3U;
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bool b1 = READ_BIT(payload, n) != 0x00U;
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n--;
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bool b2 = READ_BIT(payload, n) != 0x00U;
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n--;
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bool b3 = READ_BIT(payload, n) != 0x00U;
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unsigned char tribit = 0U;
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tribit |= b1 ? 4U : 0U;
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tribit |= b2 ? 2U : 0U;
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tribit |= b3 ? 1U : 0U;
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tribits[i] = tribit;
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}
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tribits[48U] = 0U;
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}
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void CDMRTrellis::tribitsToBits(const unsigned char* tribits, unsigned char* payload) const
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{
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for (unsigned int i = 0U; i < 48U; i++) {
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unsigned char tribit = tribits[i];
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bool b1 = (tribit & 0x04U) == 0x04U;
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bool b2 = (tribit & 0x02U) == 0x02U;
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bool b3 = (tribit & 0x01U) == 0x01U;
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unsigned int n = 143U - i * 3U;
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WRITE_BIT(payload, n, b1);
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n--;
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WRITE_BIT(payload, n, b2);
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n--;
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WRITE_BIT(payload, n, b3);
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}
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}
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bool CDMRTrellis::fixCode(unsigned char* points, unsigned int failPos, unsigned char* payload) const
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{
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for (unsigned j = 0U; j < 20U; j++) {
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unsigned int bestPos = 0U;
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unsigned int bestVal = 0U;
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for (unsigned int i = 0U; i < 16U; i++) {
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points[failPos] = i;
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unsigned char tribits[49U];
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unsigned int pos = checkCode(points, tribits);
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if (pos == 999U) {
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tribitsToBits(tribits, payload);
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return true;
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}
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if (pos > bestPos) {
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bestPos = pos;
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bestVal = i;
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}
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}
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points[failPos] = bestVal;
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failPos = bestPos;
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}
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return false;
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}
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unsigned int CDMRTrellis::checkCode(const unsigned char* points, unsigned char* tribits) const
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{
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unsigned char state = 0U;
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for (unsigned int i = 0U; i < 49U; i++) {
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tribits[i] = 9U;
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for (unsigned int j = 0U; j < 8U; j++) {
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if (points[i] == ENCODE_TABLE[state * 8U + j]) {
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tribits[i] = j;
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break;
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}
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}
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if (tribits[i] == 9U)
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return i;
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state = tribits[i];
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}
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if (tribits[48U] != 0U)
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return 48U;
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return 999U;
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}
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