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7fcf035337
Golay24.checkAndCorrect indexed the word from bit 0 (getInt(0, 22), xor(12, ...), flip(index)) and took the parity over the whole message, so it was only right for a message that is exactly one 24-bit word. P25 TDULC words 2-12 and the DMR voice superframe words at 24 and 48 were "corrected" in the wrong bits. Decode any other word in a 24-bit copy and write it back. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
86 lines
2.7 KiB
Java
86 lines
2.7 KiB
Java
/*
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* *****************************************************************************
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* Copyright (C) 2014-2026 Dennis Sheirer
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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 3 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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package io.github.dsheirer.edac;
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import io.github.dsheirer.bits.CorrectedBinaryMessage;
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import java.util.Random;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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/**
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* Tests Golay(24,12) correction of the data bits of words that are not at the start of a 24-bit message.
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*/
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public class Golay24OffsetTest
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{
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private static int encode(int data)
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{
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int checksum = 0;
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for(int bit = 0; bit < 12; bit++)
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{
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if((data & (1 << (11 - bit))) != 0)
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{
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checksum ^= Golay24.CHECKSUMS[bit];
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}
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}
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int word23 = (data << 11) | checksum;
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return (word23 << 1) | (Integer.bitCount(word23) & 1);
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}
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@Test
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public void correctsUpToThreeErrorsInEveryWordOfALongerMessage()
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{
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Random random = new Random(1);
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for(int trial = 0; trial < 2000; trial++)
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{
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int[] words = new int[3];
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CorrectedBinaryMessage message = new CorrectedBinaryMessage(72);
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for(int w = 0; w < 3; w++)
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{
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words[w] = encode(random.nextInt(4096));
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int received = words[w];
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for(int e = random.nextInt(4); e > 0; e--)
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{
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received ^= 1 << random.nextInt(24);
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}
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message.load(w * 24, 24, received);
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}
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for(int w = 0; w < 3; w++)
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{
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Golay24.checkAndCorrect(message, w * 24);
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}
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for(int w = 0; w < 3; w++)
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{
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//The 12 data bits. (The core correction can leave the overall parity bit wrong when it corrects other
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//bits, which no caller reads.)
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assertEquals(words[w] >> 12, message.getInt(w * 24, w * 24 + 11), "trial " + trial + " word " + w);
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}
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}
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}
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}
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