CompositeLFSR.java

package com.thealgorithms.ciphers.a5;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public abstract class CompositeLFSR implements BaseLFSR {
    protected final List<LFSR> registers = new ArrayList<>();

    /**
     * Implements irregular clocking using the clock bit for each register
     * @return the registers discarded bit xored value
     */
    @Override
    public boolean clock() {
        boolean majorityBit = getMajorityBit();
        boolean result = false;
        for ( var register : registers ) {
            result ^= register.getLastBit();
            if ( register.getClockBit() == majorityBit )
                register.clock();
        }
        return result;
    }

    private boolean getMajorityBit() {
        Map<Boolean, Integer> bitCount = new TreeMap<>();
        bitCount.put( false, 0 );
        bitCount.put( true, 0 );

        registers.forEach( lfsr -> bitCount.put( lfsr.getClockBit(), bitCount.get( lfsr.getClockBit() ) + 1 ) );
        return bitCount.get( false ) <= bitCount.get( true );
    }
}