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https://github.com/DSheirer/sdrtrunk.git
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54 lines
2.0 KiB
Java
54 lines
2.0 KiB
Java
/*
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* *****************************************************************************
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* Copyright (C) 2014-2025 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.BinaryMessage;
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import io.github.dsheirer.bits.IntField;
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/**
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* Utility for calculating the CRC checksum for CRC-16 using polynomial 0x1021 and Initial Fill/Residual of 0xFFFF
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*/
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public class CRC16
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{
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/**
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* Calculates the 16-bit CRC checksum for the message using polynomial 0x1021 and residual 0xFFFF
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* @param message with transmitted 16-bit checksum at the end.
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* @return true if the check is correct or false if it fails the CRC check.
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*/
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public static boolean check(BinaryMessage message)
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{
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BinaryMessage copy = message.copy();
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BinaryMessage polynomial = BinaryMessage.loadHex("11021");
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polynomial.rotateLeft(3, 0, 20);
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polynomial.setSize(message.size());
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int previousX = 0;
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for(int x = copy.nextSetBit(0); x >= 0 && x < copy.size() - 16; x = copy.nextSetBit(x + 1))
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{
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polynomial.rotateRight(x - previousX, previousX, 17 + x);
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previousX = x;
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copy.xor(polynomial);
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}
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IntField crc = IntField.length16(copy.size() - 16);
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return copy.getInt(crc) == 0xFFFF;
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}
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}
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