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C4FM: bounds check the start of the buffer in the sync score (#2622)

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A lagging sync detect on the first symbol after a buffer reload, followed by a
coarse timing search that steps all the way left, scores a candidate whose first
sync symbol is one sample before the buffer start. score() only checked the end
of the buffer, so it threw ArrayIndexOutOfBoundsException: Index -1.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Steve Pinkham
2026-11-11 03:22:44 -05:00
committed by GitHub
parent 000ac51ff0
commit e7f4f655e5
2 changed files with 51 additions and 1 deletions
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2
src/main/java/io/github/dsheirer/dsp/c4fm/C4FMSymbolProcessor.java
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@@ -1313,7 +1313,7 @@ public abstract class C4FMSymbolProcessor
for(int x = 0; x < patternSymbols.length; x++)
{
if(bufferPointer < maxPointer)
if(bufferPointer >= 0 && bufferPointer < maxPointer)
{
softSymbol = interpolate(mBuffer[bufferPointer], mBuffer[bufferPointer + 1], fractional) * gain + balance;
}

50
src/test/java/io/github/dsheirer/dsp/c4fm/C4FMSymbolProcessorScoreTest.java Normal file
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@@ -0,0 +1,50 @@
/*
* *****************************************************************************
* Copyright (C) 2014-2026 Dennis Sheirer
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>
* ****************************************************************************
*/
package io.github.dsheirer.dsp.c4fm;
import io.github.dsheirer.module.decode.p25.phase1.P25P1SymbolProcessorC4FM;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
/**
* JUnit tests for the sync correlation score in the C4FM symbol processor.
*/
public class C4FMSymbolProcessorScoreTest
{
/**
* A lagging sync detect on the first symbol after a buffer reload, followed by a coarse timing search that steps
* all the way left, scores a candidate whose first sync symbol starts just before the start of the buffer.
*/
@Test
public void scoreBeforeBufferStart()
{
float samplesPerSymbol = 25000f / 4800f;
P25P1SymbolProcessorC4FM processor = new P25P1SymbolProcessorC4FM(null, null);
processor.setSamplesPerSymbol(samplesPerSymbol);
//Sync workspace, sized as in setSamplesPerSymbol(), plus a 1024 sample buffer
int syncWorkspaceLength = (int)Math.ceil((processor.mSyncDetector.getDibitLength() + 1) * samplesPerSymbol);
processor.mBuffer = new float[syncWorkspaceLength + 1024];
//Offset to the final sync symbol that puts the first sync symbol at buffer index -0.3
double offset = (processor.mSyncDetector.getDibitLength() - 1) * samplesPerSymbol - 0.3;
assertDoesNotThrow(() -> processor.score(offset, samplesPerSymbol));
}
}