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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.atlas.lib;

// NB shifting is "mod 64" -- <<64 is a no-op (not a clear).
// http://mindprod.com/jgloss/masking.html

/** Utilities for manipulating a bit pattern which are held in a 64 bit long
 *  @see BitsInt
 *  (java.util.BitSet does not allow getting the pattern as a long) 
 */ 
public final class BitsLong
{
    private BitsLong() {}

    private static int LongLen = Long.SIZE ;
    
    /** Extract the value packed into bits start (inclusive) and finish (exclusive),
     *  the value is returned shifted into the low part of the returned long.
     *  The low bit is bit zero.
     * @param bits
     * @param start
     * @param finish
     * @return long
     */ 
    
    public static final
    long unpack(long bits, int start, int finish)
    {
        check(start, finish) ;
        if ( finish == 0 ) return 0 ;
        // Remove top bits by moving up.  Clear bottom bits by them moving down.
        return (bits<<(LongLen-finish)) >>> ((LongLen-finish)+start) ;
    }

    /** Place the value into the bit pattern between start and finish
     * and returns the new value.  Leaves other bits alone.
     * @param bits
     * @param value
     * @param start
     * @param finish
     * @return long
     */
    public static final
    long pack(long bits, long value, int start, int finish)
    {
        check(start, finish) ;
        bits = clear$(bits, start, finish) ;
        long mask = mask(start, finish) ;
        bits = bits | ( (value<>> (LongLen-finish+start) ) << start  ;
    }
    

    private static final
    long mask$(int bitIndex)
    {
        return 1L << bitIndex ;
    }

    private static final
    long mask$(int start, int finish)
    {
    //        long mask = 0 ;
    //        if ( finish == Long.SIZE )
    //            // <>> (LongLen-finish) ;      // Clear the top bits
//        return mask >>> start << start ;                  // Clear the bottom bits
        return mask << (LongLen-finish) >>> (LongLen-finish+start) << start ; 
    }

    private static final
    long maskZero$(int start, int finish)
    {

        return ~mask$(start, finish) ;
    }
    
    private static final
    void check(long bitIndex)
    {
        if ( bitIndex < 0 || bitIndex >= LongLen ) throw new IllegalArgumentException("Illegal bit index: "+bitIndex) ;
    }

    private static final
    void check(long start, long finish)
    {
        if ( start < 0 || start >= LongLen ) throw new IllegalArgumentException("Illegal start: "+start) ;
        if ( finish < 0 || finish > LongLen ) throw new IllegalArgumentException("Illegal finish: "+finish) ;
        if ( start > finish )  throw new IllegalArgumentException("Illegal range: ("+start+", "+finish+")") ;
    }
    
}