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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.
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/**
 * Copyright (c) 2002-2013 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j 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 .
 */
package org.neo4j.kernel.impl.util;

import java.util.Arrays;

import org.neo4j.kernel.impl.nioneo.store.Buffer;

/**
 * Got bits to store, shift and retrieve and they are more than what fits in a long?
 * Use {@link Bits} then.
 */
public class Bits
{
    // 3: ...
    // 2:   [   23    ][   22    ][   21    ][   20    ][   19    ][   18    ][   17    ][   16    ] <--\
    //                                                                                                   |
    //    /---------------------------------------------------------------------------------------------/
    //   |
    // 1: \-[   15    ][   14    ][   13    ][   12    ][   11    ][   10    ][    9    ][    8    ] <--\
    //                                                                                                   |
    //    /---------------------------------------------------------------------------------------------/
    //   |
    // 0: \-[    7    ][    6    ][    5    ][    4    ][    3    ][    2    ][    1    ][    0    ] <---- START
    private final long[] longs;
    private final int numberOfBytes;
    private int writePosition;
    private int readPosition;
    
    /*
     * Calculate all the right overflow masks
     */
    private static final long[] RIGHT_OVERFLOW_MASKS;
    static
    {
        RIGHT_OVERFLOW_MASKS = new long[Long.SIZE];
        long mask = 1L;
        for ( int i = 0; i < RIGHT_OVERFLOW_MASKS.length; i++ )
        {
            RIGHT_OVERFLOW_MASKS[i] = mask;
            mask <<= 1;
            mask |= 0x1L;
        }
    }
    
    public static Bits bits( int numberOfBytes )
    {
        int requiredLongs = requiredLongs(numberOfBytes);
        return new Bits( new long[requiredLongs], numberOfBytes );
    }

    public static int requiredLongs(int numberOfBytes) {
        return ((numberOfBytes-1)>>3)+1; // /8
    }

    public static Bits bitsFromLongs( long[] longs )
    {
        return new Bits( longs, longs.length<<3 ); // *8
    }
    
    public static Bits bitsFromBytes( byte[] bytes )
    {
        return bitsFromBytes( bytes, 0 );
    }
    
    public static Bits bitsFromBytes( byte[] bytes, int startIndex )
    {
        final int count = bytes.length;
        Bits bits = bits( count - startIndex );
        for ( int i = startIndex; i < count; i++ ) bits.put( bytes[i] );
        return bits;
    }
    
    private Bits( long[] longs, int numberOfBytes )
    {
        this.longs = longs;
        this.numberOfBytes = numberOfBytes;
    }

    /**
     * A mask which has the {@code steps} most significant bits set to 1, all others 0.
     * It's used to carry bits over between carriers (longs) when shifting left.
     * @param steps the number of most significant bits to have set to 1 in the mask.
     * @return the created mask.
     */
    public static long leftOverflowMask( int steps )
    {
        long mask = 0L;
        for ( int i = 0; i < steps; i++ )
        {
            mask >>= 1;
            mask |= 0x8000000000000000L;
        }
        return mask;
    }
    
    /**
     * A mask which has the {@code steps} least significant bits set to 1, all others 0.
     * It's used to carry bits over between carriers (longs) when shifting right.
     * @param steps the number of least significant bits to have set to 1 in the mask.
     * @return the created mask.
     */
    public static long rightOverflowMask( int steps )
    {
        return RIGHT_OVERFLOW_MASKS[steps-1];
    }
    
    /**
     * Returns the underlying long values that has got all the bits applied.
     * The first item in the array has got the most significant bits.
     * @return the underlying long values that has got all the bits applied.
     */
    public long[] getLongs()
    {
        return longs;
    }
    
    public byte[] asBytes()
    {
        int readPositionBefore = readPosition;
        readPosition = 0;
        try
        {
            byte[] result = new byte[numberOfBytes];
            final int count = result.length;
            for ( int i = 0; i < count; i++ )
            {
                result[i] = getByte();
            }
            return result;
        }
        finally
        {
            readPosition = readPositionBefore;
        }
    }
    
    /**
     * Writes all bits to {@code buffer}.
     * @param buffer the {@link Buffer} to write to.
     * @return this instance.
     */
    public Bits apply( Buffer buffer )
    {
        int readPositionBefore = readPosition;
        readPosition = 0;
        try
        {
            // TODO byte for byte?
            int rest = numberOfBytes;
            while ( rest-- > 0 )
            {
                buffer.put( getByte() );
            }
            return this;
        }
        finally
        {
            readPosition = readPositionBefore;
        }
    }
    
    /**
     * Reads from {@code buffer} and fills up all the bits.
     * @param buffer the {@link Buffer} to read from.
     * @return this instance.
     */
    public Bits read( Buffer buffer )
    {
        // TODO byte for byte?
        int rest = numberOfBytes;
        while ( rest > 0 )
        {
            byte value = buffer.get();
            put( value );
            rest--;
        }
        return this;
    }

    /**
     * A very nice toString, showing each bit, divided into groups of bytes and
     * lines of 8 bytes.
     */
    @Override
    public String toString()
    {
        StringBuilder builder = new StringBuilder();
        for ( int longIndex = longs.length-1; longIndex >= 0; longIndex-- )
        {
            long value = longs[longIndex];
            if ( builder.length() > 0 ) builder.append( "\n" );
            builder.append( longIndex + ":" );
            numberToString( builder, value, 8 );
            if ( longIndex == 0 ) builder.append( " <-- START" );
        }
        return builder.toString();
    }
    
    public static StringBuilder numberToString( StringBuilder builder, long value, int numberOfBytes )
    {
        builder.append( "[" );
        for ( int i = 8*numberOfBytes-1; i >= 0; i-- )
        {
            if ( i > 0 && i % 8 == 0 ) builder.append( "," );
            boolean isSet = (value & (1L << i)) != 0;
            builder.append( isSet ? "1" : "0" );
        }
        builder.append( "]" );
        return builder;
    }
    
    public static String numbersToBitString( byte[] values )
    {
        StringBuilder builder = new StringBuilder();
        for ( byte value : values ) numberToString( builder, value, 1 );
        return builder.toString();
    }
    
    public static String numbersToBitString( short[] values )
    {
        StringBuilder builder = new StringBuilder();
        for ( short value : values ) numberToString( builder, value, 2 );
        return builder.toString();
    }
    
    public static String numbersToBitString( int[] values )
    {
        StringBuilder builder = new StringBuilder();
        for ( int value : values ) numberToString( builder, value, 4 );
        return builder.toString();
    }
    
    public static String numbersToBitString( long[] values )
    {
        StringBuilder builder = new StringBuilder();
        for ( long value : values ) numberToString( builder, value, 8 );
        return builder.toString();
    }
    
    @Override
    public Bits clone()
    {
        return new Bits( Arrays.copyOf( longs, longs.length ), numberOfBytes );
    }
    
    public Bits put( byte value )
    {
        return put( value, Byte.SIZE );
    }
    
    public Bits put( byte value, int steps )
    {
        return put( (long)value, steps );
    }
    
    public Bits put( short value )
    {
        return put( value, Short.SIZE );
    }
    
    public Bits put( short value, int steps )
    {
        return put( (long)value, steps );
    }

    public Bits put( int value )
    {
        return put( value, Integer.SIZE );
    }
    
    public Bits put( int value, int steps )
    {
        return put( (long)value, steps );
    }

    public Bits put( long value )
    {
        return put( value, Long.SIZE );
    }
    
    public Bits put( long value, int steps )
    {
        int lowLongIndex = writePosition >> 6; // /64
        int lowBitInLong = writePosition%64;
        int lowBitsAvailable = 64-lowBitInLong;
        long lowValueMask = rightOverflowMask( Math.min( lowBitsAvailable, steps ) );
        longs[lowLongIndex] |= ((((long)value)&lowValueMask) << lowBitInLong);
        if ( steps > lowBitsAvailable )
        {   // High bits
            long highValueMask = rightOverflowMask( steps-lowBitsAvailable );
            longs[lowLongIndex+1] |= (((long)value) >>> lowBitsAvailable)&highValueMask;
        }
        writePosition += steps;
        return this;
    }
    
    public boolean available()
    {
        return readPosition < writePosition;
    }
    
    public byte getByte()
    {
        return getByte( Byte.SIZE );
    }
    
    public byte getByte( int steps )
    {
        return (byte) getLong( steps );
    }
    
    public short getShort()
    {
        return getShort( Short.SIZE );
    }
    
    public short getShort( int steps )
    {
        return (short) getLong( steps );
    }

    public int getInt()
    {
        return getInt( Integer.SIZE );
    }
    
    public int getInt( int steps )
    {
        return (int) getLong( steps );
    }

    public long getUnsignedInt()
    {
        return getInt( Integer.SIZE ) & 0xFFFFFFFFL;
    }
    
    public long getLong()
    {
        return getLong( Long.SIZE );
    }
    
    public long getLong( int steps )
    {
        int lowLongIndex = readPosition >> 6; // 64
        int lowBitInLong = readPosition%64;
        int lowBitsAvailable = 64-lowBitInLong;
        long lowLongMask = rightOverflowMask( Math.min( lowBitsAvailable, steps ) ) << lowBitInLong;
        long lowValue = longs[lowLongIndex] & lowLongMask;
        long result = lowValue >>> lowBitInLong;
        if ( steps > lowBitsAvailable )
        {   // High bits
            long highLongMask = rightOverflowMask( steps-lowBitsAvailable );
            result |= ((longs[lowLongIndex+1] & highLongMask) << lowBitsAvailable);
        }
        readPosition += steps;
        return result;
    }
}