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port Trellis class from dvmhost to fnecore;

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Bryan Biedenkapp 2 years ago
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commit ee642ea831
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EDAC/Trellis.cs
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/**
* Digital Voice Modem - Fixed Network Equipment
* AGPLv3 Open Source. Use is subject to license terms.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* @package DVM / Fixed Network Equipment
*
*/
//
// Based on code from the MMDVMHost project. (https://github.com/g4klx/MMDVMHost)
// Licensed under the GPLv2 License (https://opensource.org/licenses/GPL-2.0)
//
/*
* Copyright (C) 2022 by Bryan Biedenkapp N2PLL
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 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 Affero General Public License for more details.
*/
using System;
namespace fnecore.EDAC
{
/// <summary>
/// Implements 1/2 rate and 3/4 rate Trellis for DMR/P25.
/// </summary>
public sealed class Trellis
{
private static readonly uint[] INTERLEAVE_TABLE = new uint[98] {
0, 1, 8, 9, 16, 17, 24, 25, 32, 33, 40, 41, 48, 49, 56, 57, 64, 65, 72, 73, 80, 81, 88, 89, 96, 97,
2, 3, 10, 11, 18, 19, 26, 27, 34, 35, 42, 43, 50, 51, 58, 59, 66, 67, 74, 75, 82, 83, 90, 91,
4, 5, 12, 13, 20, 21, 28, 29, 36, 37, 44, 45, 52, 53, 60, 61, 68, 69, 76, 77, 84, 85, 92, 93,
6, 7, 14, 15, 22, 23, 30, 31, 38, 39, 46, 47, 54, 55, 62, 63, 70, 71, 78, 79, 86, 87, 94, 95
};
private static readonly byte[] ENCODE_TABLE_34 = new byte[] {
0, 8, 4, 12, 2, 10, 6, 14,
4, 12, 2, 10, 6, 14, 0, 8,
1, 9, 5, 13, 3, 11, 7, 15,
5, 13, 3, 11, 7, 15, 1, 9,
3, 11, 7, 15, 1, 9, 5, 13,
7, 15, 1, 9, 5, 13, 3, 11,
2, 10, 6, 14, 0, 8, 4, 12,
6, 14, 0, 8, 4, 12, 2, 10
};
private static readonly byte[] ENCODE_TABLE_12 = new byte[] {
0, 15, 12, 3,
4, 11, 8, 7,
13, 2, 1, 14,
9, 6, 5, 10
};
/*
** Methods
*/
/// <summary>
/// Initializes a new instance of the <see cref="Trellis"/> class.
/// </summary>
public Trellis()
{
/* stub */
}
/// <summary>
/// Decodes 3/4 rate Trellis.
/// </summary>
/// <param name="data">Trellis symbol bytes.</param>
/// <param name="payload">Output bytes.</param>
/// <returns>True, if decoded, otherwise false.</returns>
public bool decode34(byte[] data, ref byte[] payload)
{
if (data == null)
throw new NullReferenceException("data");
if (payload == null)
throw new NullReferenceException("payload");
int[] dibits = new int[98U];
deinterleave(data, ref dibits);
byte[] points = new byte[49U];
dibitsToPoints(dibits, ref points);
// check the original code
byte[] tribits = new byte[49U];
uint failPos = checkCode34(points, ref tribits);
if (failPos == 999U) {
tribitsToBits(tribits, ref payload);
return true;
}
byte[] savePoints = new byte[49U];
for (uint i = 0U; i< 49U; i++)
savePoints[i] = points[i];
bool ret = fixCode34(points, failPos, ref payload);
if (ret)
return true;
if (failPos == 0U)
return false;
// Backtrack one place for a last go
return fixCode34(savePoints, failPos - 1U, ref payload);
}
/// <summary>
/// Encodes 3/4 rate Trellis.
/// </summary>
/// <param name="payload">Input bytes.</param>
/// <param name="data">Trellis symbol bytes.</param>
public void encode34(byte[] payload, ref byte[] data)
{
if (data == null)
throw new NullReferenceException("data");
if (payload == null)
throw new NullReferenceException("payload");
byte[] tribits = new byte[49U];
bitsToTribits(payload, ref tribits);
byte[] points = new byte[49U];
byte state = 0;
for (uint i = 0U; i < 49U; i++)
{
byte tribit = tribits[i];
points[i] = ENCODE_TABLE_34[state * 8U + tribit];
state = tribit;
}
int[] dibits = new int[98U];
pointsToDibits(points, ref dibits);
interleave(dibits, ref data);
}
/// <summary>
/// Decodes 1/2 rate Trellis.
/// </summary>
/// <param name="data">Trellis symbol bytes.</param>
/// <param name="payload">Output bytes.</param>
/// <returns>True, if decoded, otherwise false.</returns>
public bool decode12(byte[] data, ref byte[] payload)
{
if (data == null)
throw new NullReferenceException("data");
if (payload == null)
throw new NullReferenceException("payload");
int[] dibits = new int[98U];
deinterleave(data, ref dibits);
byte[] points = new byte[49U];
dibitsToPoints(dibits, ref points);
// Check the original code
byte[] bits = new byte[49U];
uint failPos = checkCode12(points, ref bits);
if (failPos == 999U)
{
dibitsToBits(bits, ref payload);
return true;
}
byte[] savePoints = new byte[49U];
for (uint i = 0U; i < 49U; i++)
savePoints[i] = points[i];
bool ret = fixCode12(points, failPos, ref payload);
if (ret)
return true;
if (failPos == 0U)
return false;
// Backtrack one place for a last go
return fixCode12(savePoints, failPos - 1U, ref payload);
}
/// <summary>
/// Encodes 1/2 rate Trellis.
/// </summary>
/// <param name="payload">Input bytes.</param>
/// <param name="data">Trellis symbol bytes.</param>
public void encode12(byte[] payload, ref byte[] data)
{
if (data == null)
throw new NullReferenceException("data");
if (payload == null)
throw new NullReferenceException("payload");
byte[] bits = new byte[49U];
bitsToDibits(payload, ref bits);
byte[] points = new byte[49U];
byte state = 0;
for (uint i = 0U; i < 49U; i++)
{
byte bit = bits[i];
points[i] = ENCODE_TABLE_12[state * 4U + bit];
state = bit;
}
int[] dibits = new int[98U];
pointsToDibits(points, ref dibits);
interleave(dibits, ref data);
}
/// <summary>
/// Helper to deinterleave the input symbols into dibits.
/// </summary>
/// <param name="data">Trellis symbol bytes.</param>
/// <param name="dibits">Dibits.</param>
private void deinterleave(byte[] data, ref int[] dibits)
{
for (uint i = 0U; i < 98U; i++) {
uint n = i * 2U + 0U;
bool b1 = FneUtils.ReadBit(data, n) != false;
n = i * 2U + 1U;
bool b2 = FneUtils.ReadBit(data, n) != false;
int dibit;
if (!b1 && b2)
dibit = +3;
else if (!b1 && !b2)
dibit = +1;
else if (b1 && !b2)
dibit = -1;
else
dibit = -3;
n = INTERLEAVE_TABLE[i];
dibits[n] = dibit;
}
}
/// <summary>
/// Helper to interleave the input dibits into symbols.
/// </summary>
/// <param name="dibits">Dibits.</param>
/// <param name="data">Trellis symbol bytes.</param>
private void interleave(int[] dibits, ref byte[] data)
{
for (uint i = 0U; i < 98U; i++) {
uint n = INTERLEAVE_TABLE[i];
bool b1, b2;
switch (dibits[n])
{
case +3:
b1 = false;
b2 = true;
break;
case +1:
b1 = false;
b2 = false;
break;
case -1:
b1 = true;
b2 = false;
break;
default:
b1 = true;
b2 = true;
break;
}
n = i * 2U + 0U;
FneUtils.WriteBit(ref data, n, b1);
n = i * 2U + 1U;
FneUtils.WriteBit(ref data, n, b2);
}
}
/// <summary>
/// Helper to map dibits to 4FSK constellation points.
/// </summary>
/// <param name="dibits">Dibits.</param>
/// <param name="points">4FSK constellation points.</param>
private void dibitsToPoints(int[] dibits, ref byte[] points)
{
for (uint i = 0U; i < 49U; i++) {
if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == -1)
points[i] = 0;
else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == -1)
points[i] = 1;
else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == -3)
points[i] = 2;
else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == -3)
points[i] = 3;
else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == -1)
points[i] = 4;
else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == -1)
points[i] = 5;
else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == -3)
points[i] = 6;
else if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == -3)
points[i] = 7;
else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == +3)
points[i] = 8;
else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == +3)
points[i] = 9;
else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == +1)
points[i] = 10;
else if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == +1)
points[i] = 11;
else if (dibits[i * 2U + 0U] == +1 && dibits[i * 2U + 1U] == +3)
points[i] = 12;
else if (dibits[i * 2U + 0U] == -1 && dibits[i * 2U + 1U] == +3)
points[i] = 13;
else if (dibits[i * 2U + 0U] == +3 && dibits[i * 2U + 1U] == +1)
points[i] = 14;
else if (dibits[i * 2U + 0U] == -3 && dibits[i * 2U + 1U] == +1)
points[i] = 15;
}
}
/// <summary>
/// Helper to map 4FSK constellation points to dibits.
/// </summary>
/// <param name="points">4FSK Constellation points.</param>
/// <param name="dibits">Dibits.</param>
private void pointsToDibits(byte[] points, ref int[] dibits)
{
for (uint i = 0U; i < 49U; i++) {
switch (points[i])
{
case 0:
dibits[i * 2U + 0U] = +1;
dibits[i * 2U + 1U] = -1;
break;
case 1:
dibits[i * 2U + 0U] = -1;
dibits[i * 2U + 1U] = -1;
break;
case 2:
dibits[i * 2U + 0U] = +3;
dibits[i * 2U + 1U] = -3;
break;
case 3:
dibits[i * 2U + 0U] = -3;
dibits[i * 2U + 1U] = -3;
break;
case 4:
dibits[i * 2U + 0U] = -3;
dibits[i * 2U + 1U] = -1;
break;
case 5:
dibits[i * 2U + 0U] = +3;
dibits[i * 2U + 1U] = -1;
break;
case 6:
dibits[i * 2U + 0U] = -1;
dibits[i * 2U + 1U] = -3;
break;
case 7:
dibits[i * 2U + 0U] = +1;
dibits[i * 2U + 1U] = -3;
break;
case 8:
dibits[i * 2U + 0U] = -3;
dibits[i * 2U + 1U] = +3;
break;
case 9:
dibits[i * 2U + 0U] = +3;
dibits[i * 2U + 1U] = +3;
break;
case 10:
dibits[i * 2U + 0U] = -1;
dibits[i * 2U + 1U] = +1;
break;
case 11:
dibits[i * 2U + 0U] = +1;
dibits[i * 2U + 1U] = +1;
break;
case 12:
dibits[i * 2U + 0U] = +1;
dibits[i * 2U + 1U] = +3;
break;
case 13:
dibits[i * 2U + 0U] = -1;
dibits[i * 2U + 1U] = +3;
break;
case 14:
dibits[i * 2U + 0U] = +3;
dibits[i * 2U + 1U] = +1;
break;
default:
dibits[i * 2U + 0U] = -3;
dibits[i * 2U + 1U] = +1;
break;
}
}
}
/// <summary>
/// Helper to convert a byte payload into tribits.
/// </summary>
/// <param name="payload">Byte payload.</param>
/// <param name="tribits">Tribits.</param>
private void bitsToTribits(byte[] payload, ref byte[] tribits)
{
for (uint i = 0U; i < 48U; i++) {
uint n = i * 3U;
bool b1 = FneUtils.ReadBit(payload, n) != false;
n++;
bool b2 = FneUtils.ReadBit(payload, n) != false;
n++;
bool b3 = FneUtils.ReadBit(payload, n) != false;
byte tribit = 0;
tribit |= (byte)(b1 ? 4U : 0U);
tribit |= (byte)(b2 ? 2U : 0U);
tribit |= (byte)(b3 ? 1U : 0U);
tribits[i] = tribit;
}
tribits[48U] = 0;
}
/// <summary>
/// Helper to convert a byte payload into dibits.
/// </summary>
/// <param name="payload">Byte payload.</param>
/// <param name="dibits">Dibits.</param>
private void bitsToDibits(byte[] payload, ref byte[] dibits)
{
for (uint i = 0U; i < 48U; i++) {
uint n = i * 2U;
bool b1 = FneUtils.ReadBit(payload, n) != false;
n++;
bool b2 = FneUtils.ReadBit(payload, n) != false;
byte dibit = 0;
dibit |= (byte)(b1 ? 2U : 0U);
dibit |= (byte)(b2 ? 1U : 0U);
dibits[i] = dibit;
}
dibits[48U] = 0;
}
/// <summary>
/// Helper to convert tribits into a byte payload.
/// </summary>
/// <param name="tribits">Tribits.</param>
/// <param name="payload">Byte payload.</param>
private void tribitsToBits(byte[] tribits, ref byte[] payload)
{
for (uint i = 0U; i < 48U; i++) {
byte tribit = tribits[i];
bool b1 = (tribit & 0x04U) == 0x04U;
bool b2 = (tribit & 0x02U) == 0x02U;
bool b3 = (tribit & 0x01U) == 0x01U;
uint n = i * 3U;
FneUtils.WriteBit(ref payload, n, b1);
n++;
FneUtils.WriteBit(ref payload, n, b2);
n++;
FneUtils.WriteBit(ref payload, n, b3);
}
}
/// <summary>
/// Helper to convert tribits into a byte payload.
/// </summary>
/// <param name="dibits">Dibits.</param>
/// <param name="payload">Byte payload.</param>
private void dibitsToBits(byte[] dibits, ref byte[] payload)
{
for (uint i = 0U; i < 48U; i++) {
byte dibit = dibits[i];
bool b1 = (dibit & 0x02U) == 0x02U;
bool b2 = (dibit & 0x01U) == 0x01U;
uint n = i * 2U;
FneUtils.WriteBit(ref payload, n, b1);
n++;
FneUtils.WriteBit(ref payload, n, b2);
}
}
/// <summary>
/// Helper to fix errors in Trellis coding.
/// </summary>
/// <param name="points">4FSK constellation points.</param>
/// <param name="failPos"></param>
/// <param name="payload">Byte payload.</param>
/// <returns>True, if error corrected, otherwise false.</returns>
private bool fixCode34(byte[] points, uint failPos, ref byte[] payload)
{
for (uint j = 0; j < 20; j++)
{
uint bestPos = 0;
byte bestVal = 0;
for (byte i = 0; i < 16; i++)
{
points[failPos] = i;
byte[] tribits = new byte[49];
uint pos = checkCode34(points, ref tribits);
if (pos == 999)
{
tribitsToBits(tribits, ref payload);
return true;
}
if (pos > bestPos)
{
bestPos = pos;
bestVal = i;
}
}
points[failPos] = bestVal;
failPos = bestPos;
}
return false;
}
/// <summary>
/// Helper to detect errors in Trellis coding.
/// </summary>
/// <param name="points">4FSK constellation points.</param>
/// <param name="tribits">Tribits.</param>
/// <returns></returns>
private uint checkCode34(byte[] points, ref byte[] tribits)
{
byte state = 0;
for (uint i = 0; i < 49; i++)
{
tribits[i] = 9;
for (byte j = 0; j < 8; j++)
{
if (points[i] == ENCODE_TABLE_34[state * 8 + j])
{
tribits[i] = j;
break;
}
}
if (tribits[i] == 9)
return i;
state = tribits[i];
}
if (tribits[48] != 0)
return 48;
return 999;
}
/// <summary>
/// Helper to fix errors in Trellis coding.
/// </summary>
/// <param name="points">4FSK constellation points.</param>
/// <param name="failPos"></param>
/// <param name="payload">Byte payload.</param>
/// <returns>True, if error corrected, otherwise false.</returns>
private bool fixCode12(byte[] points, uint failPos, ref byte[] payload)
{
for (uint j = 0; j < 20; j++) {
uint bestPos = 0;
byte bestVal = 0;
for (byte i = 0; i < 16; i++)
{
points[failPos] = i;
byte[] dibits = new byte[49];
uint pos = checkCode12(points, ref dibits);
if (pos == 999)
{
dibitsToBits(dibits, ref payload);
return true;
}
if (pos > bestPos)
{
bestPos = pos;
bestVal = i;
}
}
points[failPos] = bestVal;
failPos = bestPos;
}
return false;
}
/// <summary>
/// Helper to detect errors in Trellis coding.
/// </summary>
/// <param name="points">4FSK constellation points.</param>
/// <param name="dibits">Dibits.</param>
/// <returns></returns>
private uint checkCode12(byte[] points, ref byte[] dibits)
{
byte state = 0;
for (uint i = 0; i < 49; i++)
{
dibits[i] = 5;
for (byte j = 0; j < 4; j++)
{
if (points[i] == ENCODE_TABLE_12[state * 4 + j])
{
dibits[i] = j;
break;
}
}
if (dibits[i] == 5)
return i;
state = dibits[i];
}
if (dibits[48] != 0)
return 48;
return 999;
}
} // public sealed class Trellis
} // namespace fnecore.EDAC
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