163 lines
5.2 KiB
C++
163 lines
5.2 KiB
C++
/*
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* Copyright (C) 2016 Jonathan Naylor, G4KLX
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* Copyright (C) 2012 Ian Wraith
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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 usefulU,
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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 "Trellis.h"
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#include <cstdio>
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#include <cassert>
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#include <cstring>
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const unsigned int INTERLEAVE[] = {
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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 int STATETABLE[] = {
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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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CTrellis::CTrellis()
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{
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}
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CTrellis::~CTrellis()
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{
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}
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// Converts the 3/4 rate trellis encoded bits to plain binary
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void CTrellis::decode(const unsigned char* in, unsigned char* out)
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{
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assert(in != NULL);
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assert(out != NULL);
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int8_t dibits[98U];
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extractDiBits(in, dibits);
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uint8_t cons[49U];
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constellationOut(dibits, cons);
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uint16_t tris[49U];
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bool ret = tribitExtract(cons, tris);
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// If the output of tribitExtract() is false then we have an error so return
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if (!ret)
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return;
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binaryConvert(tris, out);
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}
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// Extract and deinterleave the dibits
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void CTrellis::extractDiBits(const unsigned char* in, int8_t* dibits) const
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{
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for (unsigned int index = 0U; index < 98U; index++) {
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unsigned int a = index * 2U;
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if (a >= 98U)
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a += 68U;
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bool b0 = READ_BIT(in, a) != 0x00U;
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a++;
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bool b1 = READ_BIT(in, a) != 0x00U;
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// Set the dibits
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// 01 = +3
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// 00 = +1
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// 10 = -1
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// 11 = -3
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uint8_t dibit = 0U;
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if (!b0 && b1) dibit = +3;
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else if (!b0 && !b1) dibit = +1;
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else if (b0 && !b1) dibit = -1;
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else if (b0 && b1) dibit = -3;
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// Deinterleave
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unsigned int deinterleave = INTERLEAVE[index];
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dibits[deinterleave] = dibit;
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}
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}
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// Extract the constellation points
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void CTrellis::constellationOut(const int8_t* dibits, uint8_t* cons) const
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{
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unsigned int index = 0U;
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for (unsigned int a = 0U; a < 98U; a += 2U, index++) {
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if ((dibits[a] == +1) && (dibits[a + 1] == -1)) cons[index] = 0;
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else if ((dibits[a] == -1) && (dibits[a + 1] == -1)) cons[index] = 1;
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else if ((dibits[a] == +3) && (dibits[a + 1] == -3)) cons[index] = 2;
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else if ((dibits[a] == -3) && (dibits[a + 1] == -3)) cons[index] = 3;
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else if ((dibits[a] == -3) && (dibits[a + 1] == -1)) cons[index] = 4;
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else if ((dibits[a] == +3) && (dibits[a + 1] == -1)) cons[index] = 5;
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else if ((dibits[a] == -1) && (dibits[a + 1] == -3)) cons[index] = 6;
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else if ((dibits[a] == +1) && (dibits[a + 1] == -3)) cons[index] = 7;
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else if ((dibits[a] == -3) && (dibits[a + 1] == +3)) cons[index] = 8;
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else if ((dibits[a] == +3) && (dibits[a + 1] == +3)) cons[index] = 9;
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else if ((dibits[a] == -1) && (dibits[a + 1] == +1)) cons[index] = 10;
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else if ((dibits[a] == +1) && (dibits[a + 1] == +1)) cons[index] = 11;
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else if ((dibits[a] == +1) && (dibits[a + 1] == +3)) cons[index] = 12;
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else if ((dibits[a] == -1) && (dibits[a + 1] == +3)) cons[index] = 13;
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else if ((dibits[a] == +3) && (dibits[a + 1] == +1)) cons[index] = 14;
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else if ((dibits[a] == -3) && (dibits[a + 1] == +1)) cons[index] = 15;
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}
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}
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// Extract tribits (as ints) from the constellation points
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bool CTrellis::tribitExtract(const uint8_t* cons, uint16_t* tris) const
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{
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unsigned int lastState = 0U;
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for (unsigned int a = 0U; a < 49U; a++) {
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// The lastState variable decides which row of STATETABLE we should use
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unsigned int rowStart = lastState * 8;
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bool match = false;
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for (unsigned int b = rowStart; b < (rowStart + 8U); b++) {
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// Check if this constellation point matches an element of this row of STATETABLE
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if (cons[a] == STATETABLE[b]) {
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// Yes it does
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match = true;
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lastState = b - rowStart;
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tris[a] = lastState;
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}
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}
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// If no match found then we have a problem
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if (!match)
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return false;
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}
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return true;
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}
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// Extract the 144 binary bits from the dibits
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void CTrellis::binaryConvert(const uint16_t* tris, unsigned char* out) const
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{
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unsigned int a = 0U;
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for (unsigned int b = 0U; b < 48U; b++) {
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// Convert three bits at a time
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WRITE_BIT(out, a, (tris[b] & 0x04U));
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a++;
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WRITE_BIT(out, a, (tris[b] & 0x02U));
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a++;
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WRITE_BIT(out, a, (tris[b] & 0x01U));
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a++;
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}
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}
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