mirror of
https://github.com/DSheirer/sdrtrunk.git
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132 lines
3.6 KiB
Java
132 lines
3.6 KiB
Java
/*******************************************************************************
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* SDR Trunk
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* Copyright (C) 2014 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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package io.github.dsheirer.bits;
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/**
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* Sync pattern matcher.
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*
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* Note: works for sync patterns up to 63 bits (integer size - 1 ) long.
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* If a 64 bit or larger sync pattern is applied, then the wrapping feature
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* of the Long.rotate methods will wrap the MSB around to the LSB and
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* corrupt the matching value.
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*/
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public class SyncPatternMatcher
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{
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private long mBits = 0;
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private long mMask = 0;
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private long mSync = 0;
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private boolean mSoftMode = false;
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private int mSoftModeErrorThreshold = 0;
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public SyncPatternMatcher(boolean[] syncPattern)
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{
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//Setup a bit mask of all ones the length of the sync pattern
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mMask = (long)((Math.pow(2, syncPattern.length)) - 1);
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//Convert the sync bits into a long value for comparison
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for(int x = 0; x < syncPattern.length; x++)
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{
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if(syncPattern[x])
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{
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mSync += 1l << (syncPattern.length - 1 - x);
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}
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}
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}
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public SyncPatternMatcher(long sync)
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{
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mSync = sync;
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mMask = getMask(sync);
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}
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/**
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* Constructs the sync pattern matcher and defines the soft mode maximum
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* number of bit errors to allow in the pattern match.
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*
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* @param sync pattern
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* @param softModeErrorThreshold - maximum bit errors (ie pattern mismatch
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* positions) when considering a sync match
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*/
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public SyncPatternMatcher(long sync, int softModeErrorThreshold)
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{
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this(sync);
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mSoftModeErrorThreshold = softModeErrorThreshold;
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}
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/**
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* Generates an all ones mask corresponding to the sync pattern
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*/
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private static long getMask(long sync)
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{
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long mask = sync;
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for(int x = 1; x < 64; x *= 2)
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{
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mask |= (mask >> x);
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}
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return mask;
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}
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public void receive(boolean bit)
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{
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//Left shift the previous value
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mBits = Long.rotateLeft(mBits, 1);
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//Apply the mask to erase the previous MSB
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mBits &= mMask;
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//Add in the new bit
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if(bit)
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{
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mBits += 1;
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}
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}
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/**
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* Indicates if the most recently received bit sequence matches the
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* sync pattern
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*/
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public boolean matches()
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{
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if(mSoftMode)
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{
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long difference = mBits ^ mSync;
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return difference == 0 ||
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Long.bitCount(difference) <= mSoftModeErrorThreshold;
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}
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else
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{
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return (mBits == mSync);
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}
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}
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/**
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* Sets the sync pattern matcher in soft mode which allows up to the soft
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* mode threshold number of bit errors when considering a sync pattern match
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*/
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public void setSoftMode(boolean softMode)
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{
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mSoftMode = softMode;
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}
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}
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