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#2105 P25 P1/2 Motorola Talker Alias CRC Check (#2106)

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Co-authored-by: Dennis Sheirer <dsheirer@github.com>
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Denny Sheirer
2024-12-06 04:33:14 -05:00
committed by GitHub
parent 4cf51405ea
commit 49cf92c7ab
6 changed files with 138 additions and 20 deletions
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53
src/main/java/io/github/dsheirer/edac/CRC16.java Normal file
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/*
* *****************************************************************************
* Copyright (C) 2014-2024 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.edac;
import io.github.dsheirer.bits.BinaryMessage;
import io.github.dsheirer.bits.IntField;
/**
* Utility for calculating the CRC checksum for CRC-16 using polynomial 0x1021 and Initial Fill/Residual of 0xFFFF
*/
public class CRC16
{
/**
* Calculates the 16-bit CRC checksum for the message using polynomial 0x1021 and residual 0xFFFF
* @param message with transmitted 16-bit checksum at the end.
* @return true if the check is correct or false if it fails the CRC check.
*/
public static boolean check(BinaryMessage message)
{
BinaryMessage copy = message.copy();
BinaryMessage polynomial = BinaryMessage.loadHex("11021");
polynomial.rotateLeft(3, 0, 20);
polynomial.setSize(message.size());
int previousX = 0;
for(int x = copy.nextSetBit(0); x < copy.size() - 16; x = copy.nextSetBit(x + 1))
{
polynomial.rotateRight(x - previousX, previousX, 17 + x);
previousX = x;
copy.xor(polynomial);
}
IntField crc = IntField.length16(copy.size() - 16);
return copy.getInt(crc) == 0xFFFF;
}
}